diff --git a/Cargo.toml b/Cargo.toml
index a2c464366f..5ab0ba8471 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,9 +9,11 @@ members = [
 	"eth2/utils/boolean-bitfield",
 	"eth2/utils/hashing",
 	"eth2/utils/honey-badger-split",
+	"eth2/utils/int_to_bytes",
 	"eth2/utils/slot_clock",
 	"eth2/utils/ssz",
-	"eth2/utils/vec_shuffle",
+	"eth2/utils/swap_or_not_shuffle",
+	"eth2/utils/fisher_yates_shuffle",
 	"beacon_node",
 	"beacon_node/db",
 	"beacon_node/beacon_chain",
diff --git a/beacon_node/beacon_chain/src/attestation_aggregator.rs b/beacon_node/beacon_chain/src/attestation_aggregator.rs
index abedf62f6a..d5b8c090f1 100644
--- a/beacon_node/beacon_chain/src/attestation_aggregator.rs
+++ b/beacon_node/beacon_chain/src/attestation_aggregator.rs
@@ -1,7 +1,8 @@
+use crate::cached_beacon_state::CachedBeaconState;
 use state_processing::validate_attestation_without_signature;
 use std::collections::{HashMap, HashSet};
 use types::{
-    beacon_state::CommitteesError, AggregateSignature, Attestation, AttestationData, BeaconState,
+    beacon_state::BeaconStateError, AggregateSignature, Attestation, AttestationData, BeaconState,
     Bitfield, ChainSpec, FreeAttestation, Signature,
 };
 
@@ -76,12 +77,12 @@ impl AttestationAggregator {
     ///  - The signature is verified against that of the validator at `validator_index`.
     pub fn process_free_attestation(
         &mut self,
-        state: &BeaconState,
+        cached_state: &CachedBeaconState,
         free_attestation: &FreeAttestation,
         spec: &ChainSpec,
-    ) -> Result<Outcome, CommitteesError> {
+    ) -> Result<Outcome, BeaconStateError> {
         let (slot, shard, committee_index) = some_or_invalid!(
-            state.attestation_slot_and_shard_for_validator(
+            cached_state.attestation_slot_and_shard_for_validator(
                 free_attestation.validator_index as usize,
                 spec,
             )?,
@@ -104,7 +105,8 @@ impl AttestationAggregator {
         let signable_message = free_attestation.data.signable_message(PHASE_0_CUSTODY_BIT);
 
         let validator_record = some_or_invalid!(
-            state
+            cached_state
+                .state
                 .validator_registry
                 .get(free_attestation.validator_index as usize),
             Message::BadValidatorIndex
diff --git a/beacon_node/beacon_chain/src/beacon_chain.rs b/beacon_node/beacon_chain/src/beacon_chain.rs
index 41ceb4e297..b2d041654a 100644
--- a/beacon_node/beacon_chain/src/beacon_chain.rs
+++ b/beacon_node/beacon_chain/src/beacon_chain.rs
@@ -1,4 +1,5 @@
 use crate::attestation_aggregator::{AttestationAggregator, Outcome as AggregationOutcome};
+use crate::cached_beacon_state::CachedBeaconState;
 use crate::checkpoint::CheckPoint;
 use db::{
     stores::{BeaconBlockStore, BeaconStateStore},
@@ -14,7 +15,7 @@ use state_processing::{
 };
 use std::sync::Arc;
 use types::{
-    beacon_state::CommitteesError,
+    beacon_state::BeaconStateError,
     readers::{BeaconBlockReader, BeaconStateReader},
     AttestationData, BeaconBlock, BeaconBlockBody, BeaconState, ChainSpec, Crosslink, Deposit,
     Epoch, Eth1Data, FreeAttestation, Hash256, PublicKey, Signature, Slot,
@@ -24,7 +25,7 @@ use types::{
 pub enum Error {
     InsufficientValidators,
     BadRecentBlockRoots,
-    CommitteesError(CommitteesError),
+    BeaconStateError(BeaconStateError),
     DBInconsistent(String),
     DBError(String),
     ForkChoiceError(ForkChoiceError),
@@ -69,6 +70,7 @@ pub struct BeaconChain<T: ClientDB + Sized, U: SlotClock, F: ForkChoice> {
     canonical_head: RwLock<CheckPoint>,
     finalized_head: RwLock<CheckPoint>,
     pub state: RwLock<BeaconState>,
+    pub cached_state: RwLock<CachedBeaconState>,
     pub spec: ChainSpec,
     pub fork_choice: RwLock<F>,
 }
@@ -99,7 +101,7 @@ where
             initial_validator_deposits,
             latest_eth1_data,
             &spec,
-        );
+        )?;
         let state_root = genesis_state.canonical_root();
         state_store.put(&state_root, &ssz_encode(&genesis_state)[..])?;
 
@@ -107,6 +109,11 @@ where
         let block_root = genesis_block.canonical_root();
         block_store.put(&block_root, &ssz_encode(&genesis_block)[..])?;
 
+        let cached_state = RwLock::new(CachedBeaconState::from_beacon_state(
+            genesis_state.clone(),
+            spec.clone(),
+        )?);
+
         let finalized_head = RwLock::new(CheckPoint::new(
             genesis_block.clone(),
             block_root,
@@ -127,6 +134,7 @@ where
             slot_clock,
             attestation_aggregator,
             state: RwLock::new(genesis_state.clone()),
+            cached_state,
             finalized_head,
             canonical_head,
             spec,
@@ -252,7 +260,8 @@ where
     ///
     /// Information is read from the present `beacon_state` shuffling, so only information from the
     /// present and prior epoch is available.
-    pub fn block_proposer(&self, slot: Slot) -> Result<usize, CommitteesError> {
+    pub fn block_proposer(&self, slot: Slot) -> Result<usize, BeaconStateError> {
+        trace!("BeaconChain::block_proposer: slot: {}", slot);
         let index = self
             .state
             .read()
@@ -273,9 +282,13 @@ where
     pub fn validator_attestion_slot_and_shard(
         &self,
         validator_index: usize,
-    ) -> Result<Option<(Slot, u64)>, CommitteesError> {
+    ) -> Result<Option<(Slot, u64)>, BeaconStateError> {
+        trace!(
+            "BeaconChain::validator_attestion_slot_and_shard: validator_index: {}",
+            validator_index
+        );
         if let Some((slot, shard, _committee)) = self
-            .state
+            .cached_state
             .read()
             .attestation_slot_and_shard_for_validator(validator_index, &self.spec)?
         {
@@ -287,6 +300,7 @@ where
 
     /// Produce an `AttestationData` that is valid for the present `slot` and given `shard`.
     pub fn produce_attestation_data(&self, shard: u64) -> Result<AttestationData, Error> {
+        trace!("BeaconChain::produce_attestation_data: shard: {}", shard);
         let justified_epoch = self.justified_epoch();
         let justified_block_root = *self
             .state
@@ -332,9 +346,7 @@ where
         let aggregation_outcome = self
             .attestation_aggregator
             .write()
-            .process_free_attestation(&self.state.read(), &free_attestation, &self.spec)?;
-        // TODO: Check this comment
-        //.map_err(|e| e.into())?;
+            .process_free_attestation(&self.cached_state.read(), &free_attestation, &self.spec)?;
 
         // return if the attestation is invalid
         if !aggregation_outcome.valid {
@@ -489,6 +501,9 @@ where
             );
             // Update the local state variable.
             *self.state.write() = state.clone();
+            // Update the cached state variable.
+            *self.cached_state.write() =
+                CachedBeaconState::from_beacon_state(state.clone(), self.spec.clone())?;
         }
 
         Ok(BlockProcessingOutcome::ValidBlock(ValidBlock::Processed))
@@ -537,9 +552,15 @@ where
             },
         };
 
-        state
-            .per_block_processing_without_verifying_block_signature(&block, &self.spec)
-            .ok()?;
+        trace!("BeaconChain::produce_block: updating state for new block.",);
+
+        let result =
+            state.per_block_processing_without_verifying_block_signature(&block, &self.spec);
+        trace!(
+            "BeaconNode::produce_block: state processing result: {:?}",
+            result
+        );
+        result.ok()?;
 
         let state_root = state.canonical_root();
 
@@ -588,8 +609,8 @@ impl From<ForkChoiceError> for Error {
     }
 }
 
-impl From<CommitteesError> for Error {
-    fn from(e: CommitteesError) -> Error {
-        Error::CommitteesError(e)
+impl From<BeaconStateError> for Error {
+    fn from(e: BeaconStateError) -> Error {
+        Error::BeaconStateError(e)
     }
 }
diff --git a/beacon_node/beacon_chain/src/cached_beacon_state.rs b/beacon_node/beacon_chain/src/cached_beacon_state.rs
new file mode 100644
index 0000000000..e14e9fe999
--- /dev/null
+++ b/beacon_node/beacon_chain/src/cached_beacon_state.rs
@@ -0,0 +1,150 @@
+use log::{debug, trace};
+use std::collections::HashMap;
+use types::{beacon_state::BeaconStateError, BeaconState, ChainSpec, Epoch, Slot};
+
+pub const CACHE_PREVIOUS: bool = false;
+pub const CACHE_CURRENT: bool = true;
+pub const CACHE_NEXT: bool = false;
+
+pub type CrosslinkCommittees = Vec<(Vec<usize>, u64)>;
+pub type Shard = u64;
+pub type CommitteeIndex = u64;
+pub type AttestationDuty = (Slot, Shard, CommitteeIndex);
+pub type AttestationDutyMap = HashMap<u64, AttestationDuty>;
+
+// TODO: CachedBeaconState is presently duplicating `BeaconState` and `ChainSpec`. This is a
+// massive memory waste, switch them to references.
+
+pub struct CachedBeaconState {
+    pub state: BeaconState,
+    committees: Vec<Vec<CrosslinkCommittees>>,
+    attestation_duties: Vec<AttestationDutyMap>,
+    next_epoch: Epoch,
+    current_epoch: Epoch,
+    previous_epoch: Epoch,
+    spec: ChainSpec,
+}
+
+impl CachedBeaconState {
+    pub fn from_beacon_state(
+        state: BeaconState,
+        spec: ChainSpec,
+    ) -> Result<Self, BeaconStateError> {
+        let current_epoch = state.current_epoch(&spec);
+        let previous_epoch = if current_epoch == spec.genesis_epoch {
+            current_epoch
+        } else {
+            current_epoch.saturating_sub(1_u64)
+        };
+        let next_epoch = state.next_epoch(&spec);
+
+        let mut committees: Vec<Vec<CrosslinkCommittees>> = Vec::with_capacity(3);
+        let mut attestation_duties: Vec<AttestationDutyMap> = Vec::with_capacity(3);
+
+        if CACHE_PREVIOUS {
+            debug!("from_beacon_state: building previous epoch cache.");
+            let cache = build_epoch_cache(&state, previous_epoch, &spec)?;
+            committees.push(cache.committees);
+            attestation_duties.push(cache.attestation_duty_map);
+        } else {
+            committees.push(vec![]);
+            attestation_duties.push(HashMap::new());
+        }
+        if CACHE_CURRENT {
+            debug!("from_beacon_state: building current epoch cache.");
+            let cache = build_epoch_cache(&state, current_epoch, &spec)?;
+            committees.push(cache.committees);
+            attestation_duties.push(cache.attestation_duty_map);
+        } else {
+            committees.push(vec![]);
+            attestation_duties.push(HashMap::new());
+        }
+        if CACHE_NEXT {
+            debug!("from_beacon_state: building next epoch cache.");
+            let cache = build_epoch_cache(&state, next_epoch, &spec)?;
+            committees.push(cache.committees);
+            attestation_duties.push(cache.attestation_duty_map);
+        } else {
+            committees.push(vec![]);
+            attestation_duties.push(HashMap::new());
+        }
+
+        Ok(Self {
+            state,
+            committees,
+            attestation_duties,
+            next_epoch,
+            current_epoch,
+            previous_epoch,
+            spec,
+        })
+    }
+
+    fn slot_to_cache_index(&self, slot: Slot) -> Option<usize> {
+        trace!("slot_to_cache_index: cache lookup");
+        match slot.epoch(self.spec.epoch_length) {
+            epoch if (epoch == self.previous_epoch) & CACHE_PREVIOUS => Some(0),
+            epoch if (epoch == self.current_epoch) & CACHE_CURRENT => Some(1),
+            epoch if (epoch == self.next_epoch) & CACHE_NEXT => Some(2),
+            _ => None,
+        }
+    }
+
+    /// Returns the `slot`, `shard` and `committee_index` for which a validator must produce an
+    /// attestation.
+    ///
+    /// Cached method.
+    ///
+    /// Spec v0.2.0
+    pub fn attestation_slot_and_shard_for_validator(
+        &self,
+        validator_index: usize,
+        _spec: &ChainSpec,
+    ) -> Result<Option<(Slot, u64, u64)>, BeaconStateError> {
+        // Get the result for this epoch.
+        let cache_index = self
+            .slot_to_cache_index(self.state.slot)
+            .expect("Current epoch should always have a cache index.");
+
+        let duties = self.attestation_duties[cache_index]
+            .get(&(validator_index as u64))
+            .and_then(|tuple| Some(*tuple));
+
+        Ok(duties)
+    }
+}
+
+struct EpochCacheResult {
+    committees: Vec<CrosslinkCommittees>,
+    attestation_duty_map: AttestationDutyMap,
+}
+
+fn build_epoch_cache(
+    state: &BeaconState,
+    epoch: Epoch,
+    spec: &ChainSpec,
+) -> Result<EpochCacheResult, BeaconStateError> {
+    let mut epoch_committees: Vec<CrosslinkCommittees> =
+        Vec::with_capacity(spec.epoch_length as usize);
+    let mut attestation_duty_map: AttestationDutyMap = HashMap::new();
+
+    for slot in epoch.slot_iter(spec.epoch_length) {
+        let slot_committees = state.get_crosslink_committees_at_slot(slot, false, spec)?;
+
+        for (committee, shard) in slot_committees {
+            for (committee_index, validator_index) in committee.iter().enumerate() {
+                attestation_duty_map.insert(
+                    *validator_index as u64,
+                    (slot, shard, committee_index as u64),
+                );
+            }
+        }
+
+        epoch_committees.push(state.get_crosslink_committees_at_slot(slot, false, spec)?)
+    }
+
+    Ok(EpochCacheResult {
+        committees: epoch_committees,
+        attestation_duty_map,
+    })
+}
diff --git a/beacon_node/beacon_chain/src/lib.rs b/beacon_node/beacon_chain/src/lib.rs
index 4dac0b672a..bc9085fbe6 100644
--- a/beacon_node/beacon_chain/src/lib.rs
+++ b/beacon_node/beacon_chain/src/lib.rs
@@ -1,5 +1,6 @@
 mod attestation_aggregator;
 mod beacon_chain;
+mod cached_beacon_state;
 mod checkpoint;
 
 pub use self::beacon_chain::{BeaconChain, Error};
diff --git a/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs b/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs
index 09621268ca..9d61952f03 100644
--- a/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs
+++ b/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs
@@ -6,7 +6,7 @@ use db::{
     stores::{BeaconBlockStore, BeaconStateStore},
     MemoryDB,
 };
-use fork_choice::{optimised_lmd_ghost::OptimisedLMDGhost, slow_lmd_ghost::SlowLMDGhost}; // import all the algorithms
+use fork_choice::OptimisedLMDGhost;
 use log::debug;
 use rayon::prelude::*;
 use slot_clock::TestingSlotClock;
@@ -128,7 +128,18 @@ impl BeaconChainHarness {
     pub fn increment_beacon_chain_slot(&mut self) -> Slot {
         let slot = self.beacon_chain.present_slot() + 1;
 
-        debug!("Incrementing BeaconChain slot to {}.", slot);
+        let nth_slot = slot
+            - slot
+                .epoch(self.spec.epoch_length)
+                .start_slot(self.spec.epoch_length);
+        let nth_epoch = slot.epoch(self.spec.epoch_length) - self.spec.genesis_epoch;
+        debug!(
+            "Advancing BeaconChain to slot {}, epoch {} (epoch height: {}, slot {} in epoch.).",
+            slot,
+            slot.epoch(self.spec.epoch_length),
+            nth_epoch,
+            nth_slot
+        );
 
         self.beacon_chain.slot_clock.set_slot(slot.as_u64());
         self.beacon_chain.advance_state(slot).unwrap();
@@ -209,6 +220,7 @@ impl BeaconChainHarness {
         self.increment_beacon_chain_slot();
 
         // Produce a new block.
+        debug!("Producing block...");
         let block = self.produce_block();
         debug!("Submitting block for processing...");
         self.beacon_chain.process_block(block).unwrap();
diff --git a/beacon_node/beacon_chain/test_harness/src/validator_harness/mod.rs b/beacon_node/beacon_chain/test_harness/src/validator_harness/mod.rs
index e22ea1a2e2..3df32fa643 100644
--- a/beacon_node/beacon_chain/test_harness/src/validator_harness/mod.rs
+++ b/beacon_node/beacon_chain/test_harness/src/validator_harness/mod.rs
@@ -10,7 +10,7 @@ use block_producer::{BlockProducer, Error as BlockPollError};
 use db::MemoryDB;
 use direct_beacon_node::DirectBeaconNode;
 use direct_duties::DirectDuties;
-use fork_choice::{optimised_lmd_ghost::OptimisedLMDGhost, slow_lmd_ghost::SlowLMDGhost};
+use fork_choice::OptimisedLMDGhost;
 use local_signer::LocalSigner;
 use slot_clock::TestingSlotClock;
 use std::sync::Arc;
diff --git a/beacon_node/beacon_chain/test_harness/tests/chain.rs b/beacon_node/beacon_chain/test_harness/tests/chain.rs
index 8be6f2a267..1a08ffcf12 100644
--- a/beacon_node/beacon_chain/test_harness/tests/chain.rs
+++ b/beacon_node/beacon_chain/test_harness/tests/chain.rs
@@ -1,19 +1,14 @@
 use env_logger::{Builder, Env};
 use log::debug;
 use test_harness::BeaconChainHarness;
-use types::{ChainSpec, Slot};
+use types::ChainSpec;
 
 #[test]
-#[ignore]
 fn it_can_build_on_genesis_block() {
-    let mut spec = ChainSpec::foundation();
-    spec.genesis_slot = Slot::new(spec.epoch_length * 8);
+    Builder::from_env(Env::default().default_filter_or("info")).init();
 
-    /*
-    spec.shard_count = spec.shard_count / 8;
-    spec.target_committee_size = spec.target_committee_size / 8;
-    */
-    let validator_count = 1000;
+    let spec = ChainSpec::few_validators();
+    let validator_count = 8;
 
     let mut harness = BeaconChainHarness::new(spec, validator_count as usize);
 
@@ -23,21 +18,22 @@ fn it_can_build_on_genesis_block() {
 #[test]
 #[ignore]
 fn it_can_produce_past_first_epoch_boundary() {
-    Builder::from_env(Env::default().default_filter_or("debug")).init();
+    Builder::from_env(Env::default().default_filter_or("info")).init();
 
-    let validator_count = 100;
+    let spec = ChainSpec::few_validators();
+    let validator_count = 8;
 
     debug!("Starting harness build...");
 
-    let mut harness = BeaconChainHarness::new(ChainSpec::foundation(), validator_count);
+    let mut harness = BeaconChainHarness::new(spec, validator_count);
 
     debug!("Harness built, tests starting..");
 
-    let blocks = harness.spec.epoch_length * 3 + 1;
+    let blocks = harness.spec.epoch_length * 2 + 1;
 
     for i in 0..blocks {
         harness.advance_chain_with_block();
-        debug!("Produced block {}/{}.", i, blocks);
+        debug!("Produced block {}/{}.", i + 1, blocks);
     }
     let dump = harness.chain_dump().expect("Chain dump failed.");
 
diff --git a/eth2/block_producer/Cargo.toml b/eth2/block_producer/Cargo.toml
index 86dde92f7b..15d1343cc1 100644
--- a/eth2/block_producer/Cargo.toml
+++ b/eth2/block_producer/Cargo.toml
@@ -5,6 +5,7 @@ authors = ["Paul Hauner <paul@paulhauner.com>"]
 edition = "2018"
 
 [dependencies]
-slot_clock = { path = "../../eth2/utils/slot_clock" }
-ssz = { path = "../../eth2/utils/ssz" }
-types = { path = "../../eth2/types" }
+int_to_bytes = { path = "../utils/int_to_bytes" }
+slot_clock = { path = "../utils/slot_clock" }
+ssz = { path = "../utils/ssz" }
+types = { path = "../types" }
diff --git a/eth2/block_producer/src/lib.rs b/eth2/block_producer/src/lib.rs
index fefaa7c043..835b3f497e 100644
--- a/eth2/block_producer/src/lib.rs
+++ b/eth2/block_producer/src/lib.rs
@@ -1,8 +1,8 @@
 pub mod test_utils;
 mod traits;
 
+use int_to_bytes::int_to_bytes32;
 use slot_clock::SlotClock;
-use ssz::ssz_encode;
 use std::sync::Arc;
 use types::{BeaconBlock, ChainSpec, Slot};
 
@@ -132,7 +132,7 @@ impl<T: SlotClock, U: BeaconNode, V: DutiesReader, W: Signer> BlockProducer<T, U
     fn produce_block(&mut self, slot: Slot) -> Result<PollOutcome, Error> {
         let randao_reveal = {
             // TODO: add domain, etc to this message. Also ensure result matches `into_to_bytes32`.
-            let message = ssz_encode(&slot.epoch(self.spec.epoch_length));
+            let message = int_to_bytes32(slot.epoch(self.spec.epoch_length).as_u64());
 
             match self
                 .signer
diff --git a/eth2/fork_choice/Cargo.toml b/eth2/fork_choice/Cargo.toml
index 566334c761..72a653032e 100644
--- a/eth2/fork_choice/Cargo.toml
+++ b/eth2/fork_choice/Cargo.toml
@@ -10,3 +10,9 @@ ssz = { path = "../utils/ssz" }
 types = { path = "../types" }
 fast-math = "0.1.1"
 byteorder = "1.3.1"
+
+[dev-dependencies]
+yaml-rust = "0.4.2"
+bls = { path = "../utils/bls" }
+slot_clock = { path = "../utils/slot_clock" }
+beacon_chain = { path = "../../beacon_node/beacon_chain" }
diff --git a/eth2/fork_choice/src/lib.rs b/eth2/fork_choice/src/lib.rs
index f79f7e8c14..c0df820c69 100644
--- a/eth2/fork_choice/src/lib.rs
+++ b/eth2/fork_choice/src/lib.rs
@@ -44,13 +44,15 @@ extern crate types;
 
 pub mod longest_chain;
 pub mod optimised_lmd_ghost;
-pub mod protolambda_lmd_ghost;
 pub mod slow_lmd_ghost;
 
 use db::stores::BeaconBlockAtSlotError;
 use db::DBError;
 use types::{BeaconBlock, Hash256};
 
+pub use longest_chain::LongestChain;
+pub use optimised_lmd_ghost::OptimisedLMDGhost;
+
 /// Defines the interface for Fork Choices. Each Fork choice will define their own data structures
 /// which can be built in block processing through the `add_block` and `add_attestation` functions.
 /// The main fork choice algorithm is specified in `find_head
@@ -83,6 +85,7 @@ pub enum ForkChoiceError {
     CannotFindBestChild,
     ChildrenNotFound,
     StorageError(String),
+    HeadNotFound,
 }
 
 impl From<DBError> for ForkChoiceError {
@@ -113,6 +116,4 @@ pub enum ForkChoiceAlgorithms {
     SlowLMDGhost,
     /// An optimised version of LMD-GHOST by Vitalik.
     OptimisedLMDGhost,
-    /// An optimised version of LMD-GHOST by Protolambda.
-    ProtoLMDGhost,
 }
diff --git a/eth2/fork_choice/src/longest_chain.rs b/eth2/fork_choice/src/longest_chain.rs
index 277d6b9509..8056c11f22 100644
--- a/eth2/fork_choice/src/longest_chain.rs
+++ b/eth2/fork_choice/src/longest_chain.rs
@@ -1,93 +1,102 @@
-use db::stores::BeaconBlockStore;
-use db::{ClientDB, DBError};
-use ssz::{Decodable, DecodeError};
+use crate::{ForkChoice, ForkChoiceError};
+use db::{stores::BeaconBlockStore, ClientDB};
 use std::sync::Arc;
 use types::{BeaconBlock, Hash256, Slot};
 
-pub enum ForkChoiceError {
-    BadSszInDatabase,
-    MissingBlock,
-    DBError(String),
-}
-
-pub fn longest_chain<T>(
-    head_block_hashes: &[Hash256],
-    block_store: &Arc<BeaconBlockStore<T>>,
-) -> Result<Option<usize>, ForkChoiceError>
+pub struct LongestChain<T>
 where
     T: ClientDB + Sized,
 {
-    let mut head_blocks: Vec<(usize, BeaconBlock)> = vec![];
+    /// List of head block hashes
+    head_block_hashes: Vec<Hash256>,
+    /// Block storage access.
+    block_store: Arc<BeaconBlockStore<T>>,
+}
 
-    /*
-     * Load all the head_block hashes from the DB as SszBeaconBlocks.
-     */
-    for (index, block_hash) in head_block_hashes.iter().enumerate() {
-        let ssz = block_store
-            .get(&block_hash)?
-            .ok_or(ForkChoiceError::MissingBlock)?;
-        let (block, _) = BeaconBlock::ssz_decode(&ssz, 0)?;
-        head_blocks.push((index, block));
-    }
-
-    /*
-     * Loop through all the head blocks and find the highest slot.
-     */
-    let highest_slot: Option<Slot> = None;
-    for (_, block) in &head_blocks {
-        let slot = block.slot;
-
-        match highest_slot {
-            None => Some(slot),
-            Some(winning_slot) => {
-                if slot > winning_slot {
-                    Some(slot)
-                } else {
-                    Some(winning_slot)
-                }
-            }
-        };
-    }
-
-    /*
-     * Loop through all the highest blocks and sort them by highest hash.
-     *
-     * Ultimately, the index of the head_block hash with the highest slot and highest block
-     * hash will be the winner.
-     */
-    match highest_slot {
-        None => Ok(None),
-        Some(highest_slot) => {
-            let mut highest_blocks = vec![];
-            for (index, block) in head_blocks {
-                if block.slot == highest_slot {
-                    highest_blocks.push((index, block))
-                }
-            }
-
-            highest_blocks.sort_by(|a, b| head_block_hashes[a.0].cmp(&head_block_hashes[b.0]));
-            let (index, _) = highest_blocks[0];
-            Ok(Some(index))
+impl<T> LongestChain<T>
+where
+    T: ClientDB + Sized,
+{
+    pub fn new(block_store: Arc<BeaconBlockStore<T>>) -> Self {
+        LongestChain {
+            head_block_hashes: Vec::new(),
+            block_store,
         }
     }
 }
 
-impl From<DecodeError> for ForkChoiceError {
-    fn from(_: DecodeError) -> Self {
-        ForkChoiceError::BadSszInDatabase
+impl<T: ClientDB + Sized> ForkChoice for LongestChain<T> {
+    fn add_block(
+        &mut self,
+        block: &BeaconBlock,
+        block_hash: &Hash256,
+    ) -> Result<(), ForkChoiceError> {
+        // add the block hash to head_block_hashes removing the parent if it exists
+        self.head_block_hashes
+            .retain(|hash| *hash != block.parent_root);
+        self.head_block_hashes.push(*block_hash);
+        Ok(())
     }
-}
 
-impl From<DBError> for ForkChoiceError {
-    fn from(e: DBError) -> Self {
-        ForkChoiceError::DBError(e.message)
+    fn add_attestation(&mut self, _: u64, _: &Hash256) -> Result<(), ForkChoiceError> {
+        // do nothing
+        Ok(())
     }
-}
 
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn test_naive_fork_choice() {
-        assert_eq!(2 + 2, 4);
+    fn find_head(&mut self, _: &Hash256) -> Result<Hash256, ForkChoiceError> {
+        let mut head_blocks: Vec<(usize, BeaconBlock)> = vec![];
+        /*
+         * Load all the head_block hashes from the DB as SszBeaconBlocks.
+         */
+        for (index, block_hash) in self.head_block_hashes.iter().enumerate() {
+            let block = self
+                .block_store
+                .get_deserialized(&block_hash)?
+                .ok_or_else(|| ForkChoiceError::MissingBeaconBlock(*block_hash))?;
+            head_blocks.push((index, block));
+        }
+
+        /*
+         * Loop through all the head blocks and find the highest slot.
+         */
+        let highest_slot = head_blocks
+            .iter()
+            .fold(Slot::from(0u64), |highest, (_, block)| {
+                std::cmp::max(block.slot, highest)
+            });
+
+        // if we find no blocks, return Error
+        if highest_slot == 0 {
+            return Err(ForkChoiceError::HeadNotFound);
+        }
+
+        /*
+         * Loop through all the highest blocks and sort them by highest hash.
+         *
+         * Ultimately, the index of the head_block hash with the highest slot and highest block
+         * hash will be the winner.
+         */
+
+        let head_index: Option<usize> =
+            head_blocks
+                .iter()
+                .fold(None, |smallest_index, (index, block)| {
+                    if block.slot == highest_slot {
+                        if smallest_index.is_none() {
+                            return Some(*index);
+                        }
+                        return Some(std::cmp::min(
+                            *index,
+                            smallest_index.expect("Cannot be None"),
+                        ));
+                    }
+                    smallest_index
+                });
+
+        if head_index.is_none() {
+            return Err(ForkChoiceError::HeadNotFound);
+        }
+
+        Ok(self.head_block_hashes[head_index.unwrap()])
     }
 }
diff --git a/eth2/fork_choice/src/optimised_lmd_ghost.rs b/eth2/fork_choice/src/optimised_lmd_ghost.rs
index dcf9c83806..6b21e39f86 100644
--- a/eth2/fork_choice/src/optimised_lmd_ghost.rs
+++ b/eth2/fork_choice/src/optimised_lmd_ghost.rs
@@ -30,8 +30,8 @@ use fast_math::log2_raw;
 use std::collections::HashMap;
 use std::sync::Arc;
 use types::{
-    readers::BeaconBlockReader, slot_epoch::Slot, slot_height::SlotHeight,
-    validator_registry::get_active_validator_indices, BeaconBlock, Hash256,
+    readers::BeaconBlockReader, validator_registry::get_active_validator_indices, BeaconBlock,
+    Hash256, Slot, SlotHeight,
 };
 
 //TODO: Pruning - Children
@@ -116,7 +116,7 @@ where
             .ok_or_else(|| ForkChoiceError::MissingBeaconState(*state_root))?;
 
         let active_validator_indices = get_active_validator_indices(
-            &current_state.validator_registry,
+            &current_state.validator_registry[..],
             block_slot.epoch(EPOCH_LENGTH),
         );
 
diff --git a/eth2/fork_choice/src/slow_lmd_ghost.rs b/eth2/fork_choice/src/slow_lmd_ghost.rs
index 44b429fa88..3184150fde 100644
--- a/eth2/fork_choice/src/slow_lmd_ghost.rs
+++ b/eth2/fork_choice/src/slow_lmd_ghost.rs
@@ -28,10 +28,8 @@ use db::{
 use std::collections::HashMap;
 use std::sync::Arc;
 use types::{
-    readers::{BeaconBlockReader, BeaconStateReader},
-    slot_epoch::Slot,
-    validator_registry::get_active_validator_indices,
-    BeaconBlock, Hash256,
+    readers::BeaconBlockReader, validator_registry::get_active_validator_indices, BeaconBlock,
+    Hash256, Slot,
 };
 
 //TODO: Pruning and syncing
diff --git a/eth2/state_processing/Cargo.toml b/eth2/state_processing/Cargo.toml
index 683475f47c..b6b0ea57c4 100644
--- a/eth2/state_processing/Cargo.toml
+++ b/eth2/state_processing/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 
 [dependencies]
 hashing = { path = "../utils/hashing" }
+int_to_bytes = { path = "../utils/int_to_bytes" }
 integer-sqrt = "0.1"
 log = "0.4"
 ssz = { path = "../utils/ssz" }
diff --git a/eth2/state_processing/src/block_processable.rs b/eth2/state_processing/src/block_processable.rs
index 1bf6022eca..c1eec9366e 100644
--- a/eth2/state_processing/src/block_processable.rs
+++ b/eth2/state_processing/src/block_processable.rs
@@ -1,9 +1,10 @@
 use crate::SlotProcessingError;
 use hashing::hash;
-use log::debug;
+use int_to_bytes::int_to_bytes32;
+use log::{debug, trace};
 use ssz::{ssz_encode, TreeHash};
 use types::{
-    beacon_state::{AttestationValidationError, CommitteesError},
+    beacon_state::{AttestationParticipantsError, BeaconStateError},
     AggregatePublicKey, Attestation, BeaconBlock, BeaconState, ChainSpec, Crosslink, Epoch, Exit,
     Fork, Hash256, PendingAttestation, PublicKey, Signature,
 };
@@ -41,10 +42,23 @@ pub enum Error {
     BadCustodyReseeds,
     BadCustodyChallenges,
     BadCustodyResponses,
-    CommitteesError(CommitteesError),
+    BeaconStateError(BeaconStateError),
     SlotProcessingError(SlotProcessingError),
 }
 
+#[derive(Debug, PartialEq)]
+pub enum AttestationValidationError {
+    IncludedTooEarly,
+    IncludedTooLate,
+    WrongJustifiedSlot,
+    WrongJustifiedRoot,
+    BadLatestCrosslinkRoot,
+    BadSignature,
+    ShardBlockRootNotZero,
+    NoBlockRoot,
+    AttestationParticipantsError(AttestationParticipantsError),
+}
+
 macro_rules! ensure {
     ($condition: expr, $result: expr) => {
         if !$condition {
@@ -110,7 +124,7 @@ fn per_block_processing_signature_optional(
     ensure!(
         bls_verify(
             &block_proposer.pubkey,
-            &ssz_encode(&state.current_epoch(spec)),
+            &int_to_bytes32(state.current_epoch(spec).as_u64()),
             &block.randao_reveal,
             get_domain(&state.fork, state.current_epoch(spec), DOMAIN_RANDAO)
         ),
@@ -205,6 +219,8 @@ fn per_block_processing_signature_optional(
         Error::MaxAttestationsExceeded
     );
 
+    debug!("Verifying {} attestations.", block.body.attestations.len());
+
     for attestation in &block.body.attestations {
         validate_attestation(&state, attestation, spec)?;
 
@@ -217,11 +233,6 @@ fn per_block_processing_signature_optional(
         state.latest_attestations.push(pending_attestation);
     }
 
-    debug!(
-        "{} attestations verified & processed.",
-        block.body.attestations.len()
-    );
-
     /*
      * Deposits
      */
@@ -298,6 +309,10 @@ fn validate_attestation_signature_optional(
     spec: &ChainSpec,
     verify_signature: bool,
 ) -> Result<(), AttestationValidationError> {
+    trace!(
+        "validate_attestation_signature_optional: attestation epoch: {}",
+        attestation.data.slot.epoch(spec.epoch_length)
+    );
     ensure!(
         attestation.data.slot + spec.min_attestation_inclusion_delay <= state.slot,
         AttestationValidationError::IncludedTooEarly
@@ -388,9 +403,9 @@ impl From<AttestationValidationError> for Error {
     }
 }
 
-impl From<CommitteesError> for Error {
-    fn from(e: CommitteesError) -> Error {
-        Error::CommitteesError(e)
+impl From<BeaconStateError> for Error {
+    fn from(e: BeaconStateError) -> Error {
+        Error::BeaconStateError(e)
     }
 }
 
@@ -399,3 +414,9 @@ impl From<SlotProcessingError> for Error {
         Error::SlotProcessingError(e)
     }
 }
+
+impl From<AttestationParticipantsError> for AttestationValidationError {
+    fn from(e: AttestationParticipantsError) -> AttestationValidationError {
+        AttestationValidationError::AttestationParticipantsError(e)
+    }
+}
diff --git a/eth2/state_processing/src/epoch_processable.rs b/eth2/state_processing/src/epoch_processable.rs
index aece61184d..11b2b224d5 100644
--- a/eth2/state_processing/src/epoch_processable.rs
+++ b/eth2/state_processing/src/epoch_processable.rs
@@ -5,7 +5,7 @@ use ssz::TreeHash;
 use std::collections::{HashMap, HashSet};
 use std::iter::FromIterator;
 use types::{
-    beacon_state::{AttestationParticipantsError, CommitteesError, InclusionError},
+    beacon_state::{AttestationParticipantsError, BeaconStateError, InclusionError},
     validator_registry::get_active_validator_indices,
     BeaconState, ChainSpec, Crosslink, Epoch, Hash256, PendingAttestation,
 };
@@ -27,7 +27,7 @@ pub enum Error {
     NoBlockRoots,
     BaseRewardQuotientIsZero,
     NoRandaoSeed,
-    CommitteesError(CommitteesError),
+    BeaconStateError(BeaconStateError),
     AttestationParticipantsError(AttestationParticipantsError),
     InclusionError(InclusionError),
     WinningRootError(WinningRootError),
@@ -144,8 +144,10 @@ impl EpochProcessable for BeaconState {
 
         let previous_epoch_attester_indices =
             self.get_attestation_participants_union(&previous_epoch_attestations[..], spec)?;
-        let previous_total_balance =
-            self.get_total_balance(&previous_epoch_attester_indices[..], spec);
+        let previous_total_balance = self.get_total_balance(
+            &get_active_validator_indices(&self.validator_registry, previous_epoch),
+            spec,
+        );
 
         /*
          * Validators targetting the previous justified slot
@@ -315,6 +317,11 @@ impl EpochProcessable for BeaconState {
 
         // for slot in self.slot.saturating_sub(2 * spec.epoch_length)..self.slot {
         for slot in self.previous_epoch(spec).slot_iter(spec.epoch_length) {
+            trace!(
+                "Finding winning root for slot: {} (epoch: {})",
+                slot,
+                slot.epoch(spec.epoch_length)
+            );
             let crosslink_committees_at_slot =
                 self.get_crosslink_committees_at_slot(slot, false, spec)?;
 
@@ -352,7 +359,8 @@ impl EpochProcessable for BeaconState {
         /*
          * Rewards and Penalities
          */
-        let base_reward_quotient = previous_total_balance.integer_sqrt();
+        let base_reward_quotient =
+            previous_total_balance.integer_sqrt() / spec.base_reward_quotient;
         if base_reward_quotient == 0 {
             return Err(Error::BaseRewardQuotientIsZero);
         }
@@ -539,6 +547,12 @@ impl EpochProcessable for BeaconState {
          */
         self.previous_calculation_epoch = self.current_calculation_epoch;
         self.previous_epoch_start_shard = self.current_epoch_start_shard;
+
+        debug!(
+            "setting previous_epoch_seed to : {}",
+            self.current_epoch_seed
+        );
+
         self.previous_epoch_seed = self.current_epoch_seed;
 
         let should_update_validator_registy = if self.finalized_epoch
@@ -553,25 +567,24 @@ impl EpochProcessable for BeaconState {
         };
 
         if should_update_validator_registy {
+            trace!("updating validator registry.");
             self.update_validator_registry(spec);
 
             self.current_calculation_epoch = next_epoch;
             self.current_epoch_start_shard = (self.current_epoch_start_shard
                 + self.get_current_epoch_committee_count(spec) as u64)
                 % spec.shard_count;
-            self.current_epoch_seed = self
-                .generate_seed(self.current_calculation_epoch, spec)
-                .ok_or_else(|| Error::NoRandaoSeed)?;
+            self.current_epoch_seed = self.generate_seed(self.current_calculation_epoch, spec)?
         } else {
+            trace!("not updating validator registry.");
             let epochs_since_last_registry_update =
                 current_epoch - self.validator_registry_update_epoch;
             if (epochs_since_last_registry_update > 1)
                 & epochs_since_last_registry_update.is_power_of_two()
             {
                 self.current_calculation_epoch = next_epoch;
-                self.current_epoch_seed = self
-                    .generate_seed(self.current_calculation_epoch, spec)
-                    .ok_or_else(|| Error::NoRandaoSeed)?;
+                self.current_epoch_seed =
+                    self.generate_seed(self.current_calculation_epoch, spec)?
             }
         }
 
@@ -689,9 +702,9 @@ impl From<InclusionError> for Error {
     }
 }
 
-impl From<CommitteesError> for Error {
-    fn from(e: CommitteesError) -> Error {
-        Error::CommitteesError(e)
+impl From<BeaconStateError> for Error {
+    fn from(e: BeaconStateError) -> Error {
+        Error::BeaconStateError(e)
     }
 }
 
diff --git a/eth2/state_processing/src/slot_processable.rs b/eth2/state_processing/src/slot_processable.rs
index 7726c50713..9e3b611fd5 100644
--- a/eth2/state_processing/src/slot_processable.rs
+++ b/eth2/state_processing/src/slot_processable.rs
@@ -1,9 +1,9 @@
 use crate::{EpochProcessable, EpochProcessingError};
-use types::{beacon_state::CommitteesError, BeaconState, ChainSpec, Hash256};
+use types::{beacon_state::BeaconStateError, BeaconState, ChainSpec, Hash256};
 
 #[derive(Debug, PartialEq)]
 pub enum Error {
-    CommitteesError(CommitteesError),
+    BeaconStateError(BeaconStateError),
     EpochProcessingError(EpochProcessingError),
 }
 
@@ -49,9 +49,9 @@ fn merkle_root(_input: &[Hash256]) -> Hash256 {
     Hash256::zero()
 }
 
-impl From<CommitteesError> for Error {
-    fn from(e: CommitteesError) -> Error {
-        Error::CommitteesError(e)
+impl From<BeaconStateError> for Error {
+    fn from(e: BeaconStateError) -> Error {
+        Error::BeaconStateError(e)
     }
 }
 
diff --git a/eth2/types/Cargo.toml b/eth2/types/Cargo.toml
index 5c5672297d..4c5be65b51 100644
--- a/eth2/types/Cargo.toml
+++ b/eth2/types/Cargo.toml
@@ -18,4 +18,7 @@ serde_derive = "1.0"
 serde_json = "1.0"
 slog = "^2.2.3"
 ssz = { path = "../utils/ssz" }
-vec_shuffle = { path = "../utils/vec_shuffle" }
+swap_or_not_shuffle = { path = "../utils/swap_or_not_shuffle" }
+
+[dev-dependencies]
+env_logger = "0.6.0"
diff --git a/eth2/types/src/beacon_state.rs b/eth2/types/src/beacon_state.rs
index 34d0a5a1fd..18b5fc989d 100644
--- a/eth2/types/src/beacon_state.rs
+++ b/eth2/types/src/beacon_state.rs
@@ -5,51 +5,38 @@ use crate::{
     Hash256, PendingAttestation, PublicKey, Signature, Slot, Validator,
 };
 use honey_badger_split::SplitExt;
+use log::trace;
 use rand::RngCore;
 use serde_derive::Serialize;
 use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
-use std::ops::Range;
-use vec_shuffle::shuffle;
+use swap_or_not_shuffle::get_permutated_index;
 
-pub enum Error {
-    InsufficientValidators,
-    BadBlockSignature,
-    InvalidEpoch(Slot, Range<Epoch>),
-    CommitteesError(CommitteesError),
-}
+mod tests;
 
 #[derive(Debug, PartialEq)]
-pub enum CommitteesError {
-    InvalidEpoch,
-    InsufficientNumberOfValidators,
-    BadRandao,
+pub enum BeaconStateError {
+    EpochOutOfBounds,
+    UnableToShuffle,
+    InsufficientRandaoMixes,
+    InsufficientValidators,
+    InsufficientBlockRoots,
+    InsufficientIndexRoots,
+    InsufficientAttestations,
+    InsufficientCommittees,
 }
 
 #[derive(Debug, PartialEq)]
 pub enum InclusionError {
-    NoIncludedAttestations,
+    /// The validator did not participate in an attestation in this period.
+    NoAttestationsForValidator,
     AttestationParticipantsError(AttestationParticipantsError),
 }
 
 #[derive(Debug, PartialEq)]
 pub enum AttestationParticipantsError {
+    /// There is no committee for the given shard in the given epoch.
     NoCommitteeForShard,
-    NoCommittees,
-    BadBitfieldLength,
-    CommitteesError(CommitteesError),
-}
-
-#[derive(Debug, PartialEq)]
-pub enum AttestationValidationError {
-    IncludedTooEarly,
-    IncludedTooLate,
-    WrongJustifiedSlot,
-    WrongJustifiedRoot,
-    BadLatestCrosslinkRoot,
-    BadSignature,
-    ShardBlockRootNotZero,
-    NoBlockRoot,
-    AttestationParticipantsError(AttestationParticipantsError),
+    BeaconStateError(BeaconStateError),
 }
 
 macro_rules! safe_add_assign {
@@ -110,7 +97,7 @@ impl BeaconState {
         initial_validator_deposits: Vec<Deposit>,
         latest_eth1_data: Eth1Data,
         spec: &ChainSpec,
-    ) -> BeaconState {
+    ) -> Result<BeaconState, BeaconStateError> {
         let initial_crosslink = Crosslink {
             epoch: spec.genesis_epoch,
             shard_block_root: spec.zero_hash,
@@ -194,11 +181,9 @@ impl BeaconState {
         ));
         genesis_state.latest_index_roots =
             vec![genesis_active_index_root; spec.latest_index_roots_length];
-        genesis_state.current_epoch_seed = genesis_state
-            .generate_seed(spec.genesis_epoch, spec)
-            .expect("Unable to generate seed.");
+        genesis_state.current_epoch_seed = genesis_state.generate_seed(spec.genesis_epoch, spec)?;
 
-        genesis_state
+        Ok(genesis_state)
     }
 
     /// Return the tree hash root for this `BeaconState`.
@@ -219,7 +204,12 @@ impl BeaconState {
     ///
     /// Spec v0.2.0
     pub fn previous_epoch(&self, spec: &ChainSpec) -> Epoch {
-        self.current_epoch(spec).saturating_sub(1_u64)
+        let current_epoch = self.current_epoch(&spec);
+        if current_epoch == spec.genesis_epoch {
+            current_epoch
+        } else {
+            current_epoch - 1
+        }
     }
 
     /// The epoch following `self.current_epoch()`.
@@ -267,23 +257,50 @@ impl BeaconState {
     /// committee is itself a list of validator indices.
     ///
     /// Spec v0.1
-    pub fn get_shuffling(&self, seed: Hash256, epoch: Epoch, spec: &ChainSpec) -> Vec<Vec<usize>> {
+    pub fn get_shuffling(
+        &self,
+        seed: Hash256,
+        epoch: Epoch,
+        spec: &ChainSpec,
+    ) -> Option<Vec<Vec<usize>>> {
         let active_validator_indices =
             get_active_validator_indices(&self.validator_registry, epoch);
 
+        if active_validator_indices.is_empty() {
+            return None;
+        }
+
+        trace!(
+            "get_shuffling: active_validator_indices.len() == {}",
+            active_validator_indices.len()
+        );
+
         let committees_per_epoch =
             self.get_epoch_committee_count(active_validator_indices.len(), spec);
 
-        // TODO: check that Hash256::from(u64) matches 'int_to_bytes32'.
-        let seed = seed ^ Hash256::from(epoch.as_u64());
-        // TODO: fix `expect` assert.
-        let shuffled_active_validator_indices =
-            shuffle(&seed, active_validator_indices).expect("Max validator count exceed!");
+        trace!(
+            "get_shuffling: active_validator_indices.len() == {}, committees_per_epoch: {}",
+            active_validator_indices.len(),
+            committees_per_epoch
+        );
 
-        shuffled_active_validator_indices
-            .honey_badger_split(committees_per_epoch as usize)
-            .map(|slice: &[usize]| slice.to_vec())
-            .collect()
+        let mut shuffled_active_validator_indices = vec![0; active_validator_indices.len()];
+        for &i in &active_validator_indices {
+            let shuffled_i = get_permutated_index(
+                i,
+                active_validator_indices.len(),
+                &seed[..],
+                spec.shuffle_round_count,
+            )?;
+            shuffled_active_validator_indices[i] = active_validator_indices[shuffled_i]
+        }
+
+        Some(
+            shuffled_active_validator_indices
+                .honey_badger_split(committees_per_epoch as usize)
+                .map(|slice: &[usize]| slice.to_vec())
+                .collect(),
+        )
     }
 
     /// Return the number of committees in the previous epoch.
@@ -321,9 +338,17 @@ impl BeaconState {
             + 1;
         let latest_index_root = current_epoch + spec.entry_exit_delay;
 
-        if (epoch <= earliest_index_root) & (epoch >= latest_index_root) {
+        trace!(
+            "get_active_index_root: epoch: {}, earliest: {}, latest: {}",
+            epoch,
+            earliest_index_root,
+            latest_index_root
+        );
+
+        if (epoch >= earliest_index_root) & (epoch <= latest_index_root) {
             Some(self.latest_index_roots[epoch.as_usize() % spec.latest_index_roots_length])
         } else {
+            trace!("get_active_index_root: epoch out of range.");
             None
         }
     }
@@ -331,12 +356,27 @@ impl BeaconState {
     /// Generate a seed for the given ``epoch``.
     ///
     /// Spec v0.2.0
-    pub fn generate_seed(&self, epoch: Epoch, spec: &ChainSpec) -> Option<Hash256> {
-        let mut input = self.get_randao_mix(epoch, spec)?.to_vec();
-        input.append(&mut self.get_active_index_root(epoch, spec)?.to_vec());
+    pub fn generate_seed(
+        &self,
+        epoch: Epoch,
+        spec: &ChainSpec,
+    ) -> Result<Hash256, BeaconStateError> {
+        let mut input = self
+            .get_randao_mix(epoch, spec)
+            .ok_or_else(|| BeaconStateError::InsufficientRandaoMixes)?
+            .to_vec();
+
+        input.append(
+            &mut self
+                .get_active_index_root(epoch, spec)
+                .ok_or_else(|| BeaconStateError::InsufficientIndexRoots)?
+                .to_vec(),
+        );
+
         // TODO: ensure `Hash256::from(u64)` == `int_to_bytes32`.
         input.append(&mut Hash256::from(epoch.as_u64()).to_vec());
-        Some(Hash256::from(&hash(&input[..])[..]))
+
+        Ok(Hash256::from(&hash(&input[..])[..]))
     }
 
     /// Return the list of ``(committee, shard)`` tuples for the ``slot``.
@@ -350,39 +390,36 @@ impl BeaconState {
         slot: Slot,
         registry_change: bool,
         spec: &ChainSpec,
-    ) -> Result<Vec<(Vec<usize>, u64)>, CommitteesError> {
+    ) -> Result<Vec<(Vec<usize>, u64)>, BeaconStateError> {
         let epoch = slot.epoch(spec.epoch_length);
         let current_epoch = self.current_epoch(spec);
-        let previous_epoch = if current_epoch == spec.genesis_epoch {
-            current_epoch
-        } else {
-            current_epoch.saturating_sub(1_u64)
-        };
+        let previous_epoch = self.previous_epoch(spec);
         let next_epoch = self.next_epoch(spec);
 
         let (committees_per_epoch, seed, shuffling_epoch, shuffling_start_shard) =
-            if epoch == previous_epoch {
-                (
-                    self.get_previous_epoch_committee_count(spec),
-                    self.previous_epoch_seed,
-                    self.previous_calculation_epoch,
-                    self.previous_epoch_start_shard,
-                )
-            } else if epoch == current_epoch {
+            if epoch == current_epoch {
+                trace!("get_crosslink_committees_at_slot: current_epoch");
                 (
                     self.get_current_epoch_committee_count(spec),
                     self.current_epoch_seed,
                     self.current_calculation_epoch,
                     self.current_epoch_start_shard,
                 )
+            } else if epoch == previous_epoch {
+                trace!("get_crosslink_committees_at_slot: previous_epoch");
+                (
+                    self.get_previous_epoch_committee_count(spec),
+                    self.previous_epoch_seed,
+                    self.previous_calculation_epoch,
+                    self.previous_epoch_start_shard,
+                )
             } else if epoch == next_epoch {
+                trace!("get_crosslink_committees_at_slot: next_epoch");
                 let current_committees_per_epoch = self.get_current_epoch_committee_count(spec);
                 let epochs_since_last_registry_update =
                     current_epoch - self.validator_registry_update_epoch;
                 let (seed, shuffling_start_shard) = if registry_change {
-                    let next_seed = self
-                        .generate_seed(next_epoch, spec)
-                        .ok_or_else(|| CommitteesError::BadRandao)?;
+                    let next_seed = self.generate_seed(next_epoch, spec)?;
                     (
                         next_seed,
                         (self.current_epoch_start_shard + current_committees_per_epoch)
@@ -391,9 +428,7 @@ impl BeaconState {
                 } else if (epochs_since_last_registry_update > 1)
                     & epochs_since_last_registry_update.is_power_of_two()
                 {
-                    let next_seed = self
-                        .generate_seed(next_epoch, spec)
-                        .ok_or_else(|| CommitteesError::BadRandao)?;
+                    let next_seed = self.generate_seed(next_epoch, spec)?;
                     (next_seed, self.current_epoch_start_shard)
                 } else {
                     (self.current_epoch_seed, self.current_epoch_start_shard)
@@ -405,15 +440,24 @@ impl BeaconState {
                     shuffling_start_shard,
                 )
             } else {
-                panic!("Epoch out-of-bounds.")
+                return Err(BeaconStateError::EpochOutOfBounds);
             };
 
-        let shuffling = self.get_shuffling(seed, shuffling_epoch, spec);
+        let shuffling = self
+            .get_shuffling(seed, shuffling_epoch, spec)
+            .ok_or_else(|| BeaconStateError::UnableToShuffle)?;
         let offset = slot.as_u64() % spec.epoch_length;
         let committees_per_slot = committees_per_epoch / spec.epoch_length;
         let slot_start_shard =
             (shuffling_start_shard + committees_per_slot * offset) % spec.shard_count;
 
+        trace!(
+            "get_crosslink_committees_at_slot: committees_per_slot: {}, slot_start_shard: {}, seed: {}",
+            committees_per_slot,
+            slot_start_shard,
+            seed
+        );
+
         let mut crosslinks_at_slot = vec![];
         for i in 0..committees_per_slot {
             let tuple = (
@@ -433,7 +477,7 @@ impl BeaconState {
         &self,
         validator_index: usize,
         spec: &ChainSpec,
-    ) -> Result<Option<(Slot, u64, u64)>, CommitteesError> {
+    ) -> Result<Option<(Slot, u64, u64)>, BeaconStateError> {
         let mut result = None;
         for slot in self.current_epoch(spec).slot_iter(spec.epoch_length) {
             for (committee, shard) in self.get_crosslink_committees_at_slot(slot, false, spec)? {
@@ -463,16 +507,20 @@ impl BeaconState {
         &self,
         slot: Slot,
         spec: &ChainSpec,
-    ) -> Result<usize, CommitteesError> {
+    ) -> Result<usize, BeaconStateError> {
         let committees = self.get_crosslink_committees_at_slot(slot, false, spec)?;
+        trace!(
+            "get_beacon_proposer_index: slot: {}, committees_count: {}",
+            slot,
+            committees.len()
+        );
         committees
             .first()
-            .ok_or(CommitteesError::InsufficientNumberOfValidators)
+            .ok_or(BeaconStateError::InsufficientValidators)
             .and_then(|(first_committee, _)| {
                 let index = (slot.as_usize())
                     .checked_rem(first_committee.len())
-                    .ok_or(CommitteesError::InsufficientNumberOfValidators)?;
-                // NOTE: next index will not panic as we have already returned if this is the case.
+                    .ok_or(BeaconStateError::InsufficientValidators)?;
                 Ok(first_committee[index])
             })
     }
@@ -708,7 +756,7 @@ impl BeaconState {
         &mut self,
         validator_index: usize,
         spec: &ChainSpec,
-    ) -> Result<(), CommitteesError> {
+    ) -> Result<(), BeaconStateError> {
         self.exit_validator(validator_index, spec);
         let current_epoch = self.current_epoch(spec);
 
@@ -828,7 +876,7 @@ impl BeaconState {
         let earliest_attestation_index = included_attestations
             .iter()
             .min_by_key(|i| attestations[**i].inclusion_slot)
-            .ok_or_else(|| InclusionError::NoIncludedAttestations)?;
+            .ok_or_else(|| InclusionError::NoAttestationsForValidator)?;
         Ok(attestations[*earliest_attestation_index].clone())
     }
 
@@ -933,34 +981,18 @@ fn hash_tree_root<T: TreeHash>(input: Vec<T>) -> Hash256 {
     Hash256::from(&input.hash_tree_root()[..])
 }
 
-impl From<AttestationParticipantsError> for AttestationValidationError {
-    fn from(e: AttestationParticipantsError) -> AttestationValidationError {
-        AttestationValidationError::AttestationParticipantsError(e)
+impl From<BeaconStateError> for AttestationParticipantsError {
+    fn from(e: BeaconStateError) -> AttestationParticipantsError {
+        AttestationParticipantsError::BeaconStateError(e)
     }
 }
 
-impl From<CommitteesError> for AttestationParticipantsError {
-    fn from(e: CommitteesError) -> AttestationParticipantsError {
-        AttestationParticipantsError::CommitteesError(e)
-    }
-}
-
-/*
-
-*/
-
 impl From<AttestationParticipantsError> for InclusionError {
     fn from(e: AttestationParticipantsError) -> InclusionError {
         InclusionError::AttestationParticipantsError(e)
     }
 }
 
-impl From<CommitteesError> for Error {
-    fn from(e: CommitteesError) -> Error {
-        Error::CommitteesError(e)
-    }
-}
-
 impl Encodable for BeaconState {
     fn ssz_append(&self, s: &mut SszStream) {
         s.append(&self.slot);
@@ -1115,33 +1147,3 @@ impl<T: RngCore> TestRandom<T> for BeaconState {
         }
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
-    use ssz::ssz_encode;
-
-    #[test]
-    pub fn test_ssz_round_trip() {
-        let mut rng = XorShiftRng::from_seed([42; 16]);
-        let original = BeaconState::random_for_test(&mut rng);
-
-        let bytes = ssz_encode(&original);
-        let (decoded, _) = <_>::ssz_decode(&bytes, 0).unwrap();
-
-        assert_eq!(original, decoded);
-    }
-
-    #[test]
-    pub fn test_hash_tree_root() {
-        let mut rng = XorShiftRng::from_seed([42; 16]);
-        let original = BeaconState::random_for_test(&mut rng);
-
-        let result = original.hash_tree_root();
-
-        assert_eq!(result.len(), 32);
-        // TODO: Add further tests
-        // https://github.com/sigp/lighthouse/issues/170
-    }
-}
diff --git a/eth2/types/src/beacon_state/tests.rs b/eth2/types/src/beacon_state/tests.rs
new file mode 100644
index 0000000000..e069e462eb
--- /dev/null
+++ b/eth2/types/src/beacon_state/tests.rs
@@ -0,0 +1,97 @@
+#![cfg(test)]
+
+use super::*;
+use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
+use crate::{
+    beacon_state::BeaconStateError, BeaconState, ChainSpec, Deposit, DepositData, DepositInput,
+    Eth1Data, Hash256, Keypair,
+};
+use bls::create_proof_of_possession;
+use ssz::ssz_encode;
+
+struct BeaconStateTestBuilder {
+    pub genesis_time: u64,
+    pub initial_validator_deposits: Vec<Deposit>,
+    pub latest_eth1_data: Eth1Data,
+    pub spec: ChainSpec,
+    pub keypairs: Vec<Keypair>,
+}
+
+impl BeaconStateTestBuilder {
+    pub fn with_random_validators(validator_count: usize) -> Self {
+        let genesis_time = 10_000_000;
+        let keypairs: Vec<Keypair> = (0..validator_count)
+            .collect::<Vec<usize>>()
+            .iter()
+            .map(|_| Keypair::random())
+            .collect();
+        let initial_validator_deposits = keypairs
+            .iter()
+            .map(|keypair| Deposit {
+                branch: vec![], // branch verification is not specified.
+                index: 0,       // index verification is not specified.
+                deposit_data: DepositData {
+                    amount: 32_000_000_000, // 32 ETH (in Gwei)
+                    timestamp: genesis_time - 1,
+                    deposit_input: DepositInput {
+                        pubkey: keypair.pk.clone(),
+                        withdrawal_credentials: Hash256::zero(), // Withdrawal not possible.
+                        proof_of_possession: create_proof_of_possession(&keypair),
+                    },
+                },
+            })
+            .collect();
+        let latest_eth1_data = Eth1Data {
+            deposit_root: Hash256::zero(),
+            block_hash: Hash256::zero(),
+        };
+        let spec = ChainSpec::foundation();
+
+        Self {
+            genesis_time,
+            initial_validator_deposits,
+            latest_eth1_data,
+            spec,
+            keypairs,
+        }
+    }
+
+    pub fn build(&self) -> Result<BeaconState, BeaconStateError> {
+        BeaconState::genesis(
+            self.genesis_time,
+            self.initial_validator_deposits.clone(),
+            self.latest_eth1_data.clone(),
+            &self.spec,
+        )
+    }
+}
+
+#[test]
+pub fn can_produce_genesis_block() {
+    let builder = BeaconStateTestBuilder::with_random_validators(2);
+
+    builder.build().unwrap();
+}
+
+#[test]
+pub fn test_ssz_round_trip() {
+    let mut rng = XorShiftRng::from_seed([42; 16]);
+    let original = BeaconState::random_for_test(&mut rng);
+
+    let bytes = ssz_encode(&original);
+    let (decoded, _) = <_>::ssz_decode(&bytes, 0).unwrap();
+
+    assert_eq!(original, decoded);
+}
+
+#[test]
+pub fn test_hash_tree_root() {
+    let mut rng = XorShiftRng::from_seed([42; 16]);
+    let original = BeaconState::random_for_test(&mut rng);
+
+    let result = original.hash_tree_root();
+
+    assert_eq!(result.len(), 32);
+    // TODO: Add further tests
+    // https://github.com/sigp/lighthouse/issues/170
+}
diff --git a/eth2/types/src/spec/foundation.rs b/eth2/types/src/chain_spec.rs
similarity index 54%
rename from eth2/types/src/spec/foundation.rs
rename to eth2/types/src/chain_spec.rs
index 79abe40615..b5d5689e38 100644
--- a/eth2/types/src/spec/foundation.rs
+++ b/eth2/types/src/chain_spec.rs
@@ -1,7 +1,96 @@
-use crate::{Address, ChainSpec, Epoch, Hash256, Signature, Slot};
+use crate::{Address, Epoch, Hash256, Slot};
+use bls::Signature;
 
 const GWEI: u64 = 1_000_000_000;
 
+/// Holds all the "constants" for a BeaconChain.
+///
+/// Spec v0.2.0
+#[derive(PartialEq, Debug, Clone)]
+pub struct ChainSpec {
+    /*
+     * Misc
+     */
+    pub shard_count: u64,
+    pub target_committee_size: u64,
+    pub max_balance_churn_quotient: u64,
+    pub beacon_chain_shard_number: u64,
+    pub max_indices_per_slashable_vote: u64,
+    pub max_withdrawals_per_epoch: u64,
+    pub shuffle_round_count: u8,
+
+    /*
+     *  Deposit contract
+     */
+    pub deposit_contract_address: Address,
+    pub deposit_contract_tree_depth: u64,
+
+    /*
+     *  Gwei values
+     */
+    pub min_deposit_amount: u64,
+    pub max_deposit_amount: u64,
+    pub fork_choice_balance_increment: u64,
+    pub ejection_balance: u64,
+
+    /*
+     * Initial Values
+     */
+    pub genesis_fork_version: u64,
+    pub genesis_slot: Slot,
+    pub genesis_epoch: Epoch,
+    pub genesis_start_shard: u64,
+    pub far_future_epoch: Epoch,
+    pub zero_hash: Hash256,
+    pub empty_signature: Signature,
+    pub bls_withdrawal_prefix_byte: u8,
+
+    /*
+     * Time parameters
+     */
+    pub slot_duration: u64,
+    pub min_attestation_inclusion_delay: u64,
+    pub epoch_length: u64,
+    pub seed_lookahead: Epoch,
+    pub entry_exit_delay: u64,
+    pub eth1_data_voting_period: u64,
+    pub min_validator_withdrawal_epochs: Epoch,
+
+    /*
+     * State list lengths
+     */
+    pub latest_block_roots_length: usize,
+    pub latest_randao_mixes_length: usize,
+    pub latest_index_roots_length: usize,
+    pub latest_penalized_exit_length: usize,
+
+    /*
+     * Reward and penalty quotients
+     */
+    pub base_reward_quotient: u64,
+    pub whistleblower_reward_quotient: u64,
+    pub includer_reward_quotient: u64,
+    pub inactivity_penalty_quotient: u64,
+
+    /*
+     * Max operations per block
+     */
+    pub max_proposer_slashings: u64,
+    pub max_attester_slashings: u64,
+    pub max_attestations: u64,
+    pub max_deposits: u64,
+    pub max_exits: u64,
+
+    /*
+     * Signature domains
+     */
+    pub domain_deposit: u64,
+    pub domain_attestation: u64,
+    pub domain_proposal: u64,
+    pub domain_exit: u64,
+    pub domain_randao: u64,
+}
+
 impl ChainSpec {
     /// Returns a `ChainSpec` compatible with the specification from Ethereum Foundation.
     ///
@@ -100,6 +189,26 @@ impl ChainSpec {
     }
 }
 
+impl ChainSpec {
+    /// Returns a `ChainSpec` compatible with the specification suitable for 8 validators.
+    ///
+    /// Spec v0.2.0
+    pub fn few_validators() -> Self {
+        let genesis_slot = Slot::new(2_u64.pow(19));
+        let epoch_length = 8;
+        let genesis_epoch = genesis_slot.epoch(epoch_length);
+
+        Self {
+            shard_count: 1,
+            target_committee_size: 1,
+            genesis_slot,
+            genesis_epoch,
+            epoch_length,
+            ..ChainSpec::foundation()
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/eth2/types/src/lib.rs b/eth2/types/src/lib.rs
index 5895934827..f2c128440a 100644
--- a/eth2/types/src/lib.rs
+++ b/eth2/types/src/lib.rs
@@ -8,6 +8,7 @@ pub mod beacon_block;
 pub mod beacon_block_body;
 pub mod beacon_state;
 pub mod casper_slashing;
+pub mod chain_spec;
 pub mod crosslink;
 pub mod deposit;
 pub mod deposit_data;
@@ -24,9 +25,10 @@ pub mod readers;
 pub mod shard_reassignment_record;
 pub mod slashable_attestation;
 pub mod slashable_vote_data;
+#[macro_use]
+pub mod slot_epoch_macros;
 pub mod slot_epoch;
 pub mod slot_height;
-pub mod spec;
 pub mod validator;
 pub mod validator_registry;
 pub mod validator_registry_delta_block;
@@ -42,6 +44,7 @@ pub use crate::beacon_block::BeaconBlock;
 pub use crate::beacon_block_body::BeaconBlockBody;
 pub use crate::beacon_state::BeaconState;
 pub use crate::casper_slashing::CasperSlashing;
+pub use crate::chain_spec::ChainSpec;
 pub use crate::crosslink::Crosslink;
 pub use crate::deposit::Deposit;
 pub use crate::deposit_data::DepositData;
@@ -58,7 +61,6 @@ pub use crate::slashable_attestation::SlashableAttestation;
 pub use crate::slashable_vote_data::SlashableVoteData;
 pub use crate::slot_epoch::{Epoch, Slot};
 pub use crate::slot_height::SlotHeight;
-pub use crate::spec::ChainSpec;
 pub use crate::validator::{StatusFlags as ValidatorStatusFlags, Validator};
 pub use crate::validator_registry_delta_block::ValidatorRegistryDeltaBlock;
 
diff --git a/eth2/types/src/slot_epoch.rs b/eth2/types/src/slot_epoch.rs
index b7a8e8f8dd..eb5a8dced7 100644
--- a/eth2/types/src/slot_epoch.rs
+++ b/eth2/types/src/slot_epoch.rs
@@ -21,255 +21,6 @@ use std::hash::{Hash, Hasher};
 use std::iter::Iterator;
 use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Rem, Sub, SubAssign};
 
-macro_rules! impl_from_into_u64 {
-    ($main: ident) => {
-        impl From<u64> for $main {
-            fn from(n: u64) -> $main {
-                $main(n)
-            }
-        }
-
-        impl Into<u64> for $main {
-            fn into(self) -> u64 {
-                self.0
-            }
-        }
-
-        impl $main {
-            pub fn as_u64(&self) -> u64 {
-                self.0
-            }
-        }
-    };
-}
-
-macro_rules! impl_from_into_usize {
-    ($main: ident) => {
-        impl From<usize> for $main {
-            fn from(n: usize) -> $main {
-                $main(n as u64)
-            }
-        }
-
-        impl Into<usize> for $main {
-            fn into(self) -> usize {
-                self.0 as usize
-            }
-        }
-
-        impl $main {
-            pub fn as_usize(&self) -> usize {
-                self.0 as usize
-            }
-        }
-    };
-}
-
-macro_rules! impl_math_between {
-    ($main: ident, $other: ident) => {
-        impl PartialOrd<$other> for $main {
-            /// Utilizes `partial_cmp` on the underlying `u64`.
-            fn partial_cmp(&self, other: &$other) -> Option<Ordering> {
-                Some(self.0.cmp(&(*other).into()))
-            }
-        }
-
-        impl PartialEq<$other> for $main {
-            fn eq(&self, other: &$other) -> bool {
-                let other: u64 = (*other).into();
-                self.0 == other
-            }
-        }
-
-        impl Add<$other> for $main {
-            type Output = $main;
-
-            fn add(self, other: $other) -> $main {
-                $main::from(self.0.saturating_add(other.into()))
-            }
-        }
-
-        impl AddAssign<$other> for $main {
-            fn add_assign(&mut self, other: $other) {
-                self.0 = self.0.saturating_add(other.into());
-            }
-        }
-
-        impl Sub<$other> for $main {
-            type Output = $main;
-
-            fn sub(self, other: $other) -> $main {
-                $main::from(self.0.saturating_sub(other.into()))
-            }
-        }
-
-        impl SubAssign<$other> for $main {
-            fn sub_assign(&mut self, other: $other) {
-                self.0 = self.0.saturating_sub(other.into());
-            }
-        }
-
-        impl Mul<$other> for $main {
-            type Output = $main;
-
-            fn mul(self, rhs: $other) -> $main {
-                let rhs: u64 = rhs.into();
-                $main::from(self.0.saturating_mul(rhs))
-            }
-        }
-
-        impl MulAssign<$other> for $main {
-            fn mul_assign(&mut self, rhs: $other) {
-                let rhs: u64 = rhs.into();
-                self.0 = self.0.saturating_mul(rhs)
-            }
-        }
-
-        impl Div<$other> for $main {
-            type Output = $main;
-
-            fn div(self, rhs: $other) -> $main {
-                let rhs: u64 = rhs.into();
-                if rhs == 0 {
-                    panic!("Cannot divide by zero-valued Slot/Epoch")
-                }
-                $main::from(self.0 / rhs)
-            }
-        }
-
-        impl DivAssign<$other> for $main {
-            fn div_assign(&mut self, rhs: $other) {
-                let rhs: u64 = rhs.into();
-                if rhs == 0 {
-                    panic!("Cannot divide by zero-valued Slot/Epoch")
-                }
-                self.0 = self.0 / rhs
-            }
-        }
-
-        impl Rem<$other> for $main {
-            type Output = $main;
-
-            fn rem(self, modulus: $other) -> $main {
-                let modulus: u64 = modulus.into();
-                $main::from(self.0 % modulus)
-            }
-        }
-    };
-}
-
-macro_rules! impl_math {
-    ($type: ident) => {
-        impl $type {
-            pub fn saturating_sub<T: Into<$type>>(&self, other: T) -> $type {
-                *self - other.into()
-            }
-
-            pub fn saturating_add<T: Into<$type>>(&self, other: T) -> $type {
-                *self + other.into()
-            }
-
-            pub fn checked_div<T: Into<$type>>(&self, rhs: T) -> Option<$type> {
-                let rhs: $type = rhs.into();
-                if rhs == 0 {
-                    None
-                } else {
-                    Some(*self / rhs)
-                }
-            }
-
-            pub fn is_power_of_two(&self) -> bool {
-                self.0.is_power_of_two()
-            }
-        }
-
-        impl Ord for $type {
-            fn cmp(&self, other: &$type) -> Ordering {
-                let other: u64 = (*other).into();
-                self.0.cmp(&other)
-            }
-        }
-    };
-}
-
-macro_rules! impl_display {
-    ($type: ident) => {
-        impl fmt::Display for $type {
-            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-                write!(f, "{}", self.0)
-            }
-        }
-
-        impl slog::Value for $type {
-            fn serialize(
-                &self,
-                record: &slog::Record,
-                key: slog::Key,
-                serializer: &mut slog::Serializer,
-            ) -> slog::Result {
-                self.0.serialize(record, key, serializer)
-            }
-        }
-    };
-}
-
-macro_rules! impl_ssz {
-    ($type: ident) => {
-        impl Encodable for $type {
-            fn ssz_append(&self, s: &mut SszStream) {
-                s.append(&self.0);
-            }
-        }
-
-        impl Decodable for $type {
-            fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-                let (value, i) = <_>::ssz_decode(bytes, i)?;
-
-                Ok(($type(value), i))
-            }
-        }
-
-        impl TreeHash for $type {
-            fn hash_tree_root(&self) -> Vec<u8> {
-                let mut result: Vec<u8> = vec![];
-                result.append(&mut self.0.hash_tree_root());
-                hash(&result)
-            }
-        }
-
-        impl<T: RngCore> TestRandom<T> for $type {
-            fn random_for_test(rng: &mut T) -> Self {
-                $type::from(u64::random_for_test(rng))
-            }
-        }
-    };
-}
-
-macro_rules! impl_hash {
-    ($type: ident) => {
-        // Implemented to stop clippy lint:
-        // https://rust-lang.github.io/rust-clippy/master/index.html#derive_hash_xor_eq
-        impl Hash for $type {
-            fn hash<H: Hasher>(&self, state: &mut H) {
-                ssz_encode(self).hash(state)
-            }
-        }
-    };
-}
-
-macro_rules! impl_common {
-    ($type: ident) => {
-        impl_from_into_u64!($type);
-        impl_from_into_usize!($type);
-        impl_math_between!($type, $type);
-        impl_math_between!($type, u64);
-        impl_math!($type);
-        impl_display!($type);
-        impl_ssz!($type);
-        impl_hash!($type);
-    };
-}
-
 #[derive(Eq, Debug, Clone, Copy, Default, Serialize)]
 pub struct Slot(u64);
 
@@ -349,373 +100,19 @@ impl<'a> Iterator for SlotIter<'a> {
 }
 
 #[cfg(test)]
-mod tests {
+mod slot_tests {
     use super::*;
+    use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
+    use ssz::ssz_encode;
 
-    macro_rules! new_tests {
-        ($type: ident) => {
-            #[test]
-            fn new() {
-                assert_eq!($type(0), $type::new(0));
-                assert_eq!($type(3), $type::new(3));
-                assert_eq!($type(u64::max_value()), $type::new(u64::max_value()));
-            }
-        };
-    }
-
-    macro_rules! from_into_tests {
-        ($type: ident, $other: ident) => {
-            #[test]
-            fn into() {
-                let x: $other = $type(0).into();
-                assert_eq!(x, 0);
-
-                let x: $other = $type(3).into();
-                assert_eq!(x, 3);
-
-                let x: $other = $type(u64::max_value()).into();
-                // Note: this will fail on 32 bit systems. This is expected as we don't have a proper
-                // 32-bit system strategy in place.
-                assert_eq!(x, $other::max_value());
-            }
-
-            #[test]
-            fn from() {
-                assert_eq!($type(0), $type::from(0_u64));
-                assert_eq!($type(3), $type::from(3_u64));
-                assert_eq!($type(u64::max_value()), $type::from($other::max_value()));
-            }
-        };
-    }
-
-    macro_rules! math_between_tests {
-        ($type: ident, $other: ident) => {
-            #[test]
-            fn partial_ord() {
-                let assert_partial_ord = |a: u64, partial_ord: Ordering, b: u64| {
-                    let other: $other = $type(b).into();
-                    assert_eq!($type(a).partial_cmp(&other), Some(partial_ord));
-                };
-
-                assert_partial_ord(1, Ordering::Less, 2);
-                assert_partial_ord(2, Ordering::Greater, 1);
-                assert_partial_ord(0, Ordering::Less, u64::max_value());
-                assert_partial_ord(u64::max_value(), Ordering::Greater, 0);
-            }
-
-            #[test]
-            fn partial_eq() {
-                let assert_partial_eq = |a: u64, b: u64, is_equal: bool| {
-                    let other: $other = $type(b).into();
-                    assert_eq!($type(a).eq(&other), is_equal);
-                };
-
-                assert_partial_eq(0, 0, true);
-                assert_partial_eq(0, 1, false);
-                assert_partial_eq(1, 0, false);
-                assert_partial_eq(1, 1, true);
-
-                assert_partial_eq(u64::max_value(), u64::max_value(), true);
-                assert_partial_eq(0, u64::max_value(), false);
-                assert_partial_eq(u64::max_value(), 0, false);
-            }
-
-            #[test]
-            fn add_and_add_assign() {
-                let assert_add = |a: u64, b: u64, result: u64| {
-                    let other: $other = $type(b).into();
-                    assert_eq!($type(a) + other, $type(result));
-
-                    let mut add_assigned = $type(a);
-                    add_assigned += other;
-
-                    assert_eq!(add_assigned, $type(result));
-                };
-
-                assert_add(0, 1, 1);
-                assert_add(1, 0, 1);
-                assert_add(1, 2, 3);
-                assert_add(2, 1, 3);
-                assert_add(7, 7, 14);
-
-                // Addition should be saturating.
-                assert_add(u64::max_value(), 1, u64::max_value());
-                assert_add(u64::max_value(), u64::max_value(), u64::max_value());
-            }
-
-            #[test]
-            fn sub_and_sub_assign() {
-                let assert_sub = |a: u64, b: u64, result: u64| {
-                    let other: $other = $type(b).into();
-                    assert_eq!($type(a) - other, $type(result));
-
-                    let mut sub_assigned = $type(a);
-                    sub_assigned -= other;
-
-                    assert_eq!(sub_assigned, $type(result));
-                };
-
-                assert_sub(1, 0, 1);
-                assert_sub(2, 1, 1);
-                assert_sub(14, 7, 7);
-                assert_sub(u64::max_value(), 1, u64::max_value() - 1);
-                assert_sub(u64::max_value(), u64::max_value(), 0);
-
-                // Subtraction should be saturating
-                assert_sub(0, 1, 0);
-                assert_sub(1, 2, 0);
-            }
-
-            #[test]
-            fn mul_and_mul_assign() {
-                let assert_mul = |a: u64, b: u64, result: u64| {
-                    let other: $other = $type(b).into();
-                    assert_eq!($type(a) * other, $type(result));
-
-                    let mut mul_assigned = $type(a);
-                    mul_assigned *= other;
-
-                    assert_eq!(mul_assigned, $type(result));
-                };
-
-                assert_mul(2, 2, 4);
-                assert_mul(1, 2, 2);
-                assert_mul(0, 2, 0);
-
-                // Multiplication should be saturating.
-                assert_mul(u64::max_value(), 2, u64::max_value());
-            }
-
-            #[test]
-            fn div_and_div_assign() {
-                let assert_div = |a: u64, b: u64, result: u64| {
-                    let other: $other = $type(b).into();
-                    assert_eq!($type(a) / other, $type(result));
-
-                    let mut div_assigned = $type(a);
-                    div_assigned /= other;
-
-                    assert_eq!(div_assigned, $type(result));
-                };
-
-                assert_div(0, 2, 0);
-                assert_div(2, 2, 1);
-                assert_div(100, 50, 2);
-                assert_div(128, 2, 64);
-                assert_div(u64::max_value(), 2, 2_u64.pow(63) - 1);
-            }
-
-            #[test]
-            #[should_panic]
-            fn div_panics_with_divide_by_zero() {
-                let other: $other = $type(0).into();
-                let _ = $type(2) / other;
-            }
-
-            #[test]
-            #[should_panic]
-            fn div_assign_panics_with_divide_by_zero() {
-                let other: $other = $type(0).into();
-                let mut assigned = $type(2);
-                assigned /= other;
-            }
-
-            #[test]
-            fn rem() {
-                let assert_rem = |a: u64, b: u64, result: u64| {
-                    let other: $other = $type(b).into();
-                    assert_eq!($type(a) % other, $type(result));
-                };
-
-                assert_rem(3, 2, 1);
-                assert_rem(40, 2, 0);
-                assert_rem(10, 100, 10);
-                assert_rem(302042, 3293, 2379);
-            }
-        };
-    }
-
-    macro_rules! math_tests {
-        ($type: ident) => {
-            #[test]
-            fn saturating_sub() {
-                let assert_saturating_sub = |a: u64, b: u64, result: u64| {
-                    assert_eq!($type(a).saturating_sub($type(b)), $type(result));
-                };
-
-                assert_saturating_sub(1, 0, 1);
-                assert_saturating_sub(2, 1, 1);
-                assert_saturating_sub(14, 7, 7);
-                assert_saturating_sub(u64::max_value(), 1, u64::max_value() - 1);
-                assert_saturating_sub(u64::max_value(), u64::max_value(), 0);
-
-                // Subtraction should be saturating
-                assert_saturating_sub(0, 1, 0);
-                assert_saturating_sub(1, 2, 0);
-            }
-
-            #[test]
-            fn saturating_add() {
-                let assert_saturating_add = |a: u64, b: u64, result: u64| {
-                    assert_eq!($type(a).saturating_add($type(b)), $type(result));
-                };
-
-                assert_saturating_add(0, 1, 1);
-                assert_saturating_add(1, 0, 1);
-                assert_saturating_add(1, 2, 3);
-                assert_saturating_add(2, 1, 3);
-                assert_saturating_add(7, 7, 14);
-
-                // Addition should be saturating.
-                assert_saturating_add(u64::max_value(), 1, u64::max_value());
-                assert_saturating_add(u64::max_value(), u64::max_value(), u64::max_value());
-            }
-
-            #[test]
-            fn checked_div() {
-                let assert_checked_div = |a: u64, b: u64, result: Option<u64>| {
-                    let division_result_as_u64 = match $type(a).checked_div($type(b)) {
-                        None => None,
-                        Some(val) => Some(val.as_u64()),
-                    };
-                    assert_eq!(division_result_as_u64, result);
-                };
-
-                assert_checked_div(0, 2, Some(0));
-                assert_checked_div(2, 2, Some(1));
-                assert_checked_div(100, 50, Some(2));
-                assert_checked_div(128, 2, Some(64));
-                assert_checked_div(u64::max_value(), 2, Some(2_u64.pow(63) - 1));
-
-                assert_checked_div(2, 0, None);
-                assert_checked_div(0, 0, None);
-                assert_checked_div(u64::max_value(), 0, None);
-            }
-
-            #[test]
-            fn is_power_of_two() {
-                let assert_is_power_of_two = |a: u64, result: bool| {
-                    assert_eq!(
-                        $type(a).is_power_of_two(),
-                        result,
-                        "{}.is_power_of_two() != {}",
-                        a,
-                        result
-                    );
-                };
-
-                assert_is_power_of_two(0, false);
-                assert_is_power_of_two(1, true);
-                assert_is_power_of_two(2, true);
-                assert_is_power_of_two(3, false);
-                assert_is_power_of_two(4, true);
-
-                assert_is_power_of_two(2_u64.pow(4), true);
-                assert_is_power_of_two(u64::max_value(), false);
-            }
-
-            #[test]
-            fn ord() {
-                let assert_ord = |a: u64, ord: Ordering, b: u64| {
-                    assert_eq!($type(a).cmp(&$type(b)), ord);
-                };
-
-                assert_ord(1, Ordering::Less, 2);
-                assert_ord(2, Ordering::Greater, 1);
-                assert_ord(0, Ordering::Less, u64::max_value());
-                assert_ord(u64::max_value(), Ordering::Greater, 0);
-            }
-        };
-    }
-
-    macro_rules! ssz_tests {
-        ($type: ident) => {
-            #[test]
-            pub fn test_ssz_round_trip() {
-                let mut rng = XorShiftRng::from_seed([42; 16]);
-                let original = $type::random_for_test(&mut rng);
-
-                let bytes = ssz_encode(&original);
-                let (decoded, _) = $type::ssz_decode(&bytes, 0).unwrap();
-
-                assert_eq!(original, decoded);
-            }
-
-            #[test]
-            pub fn test_hash_tree_root() {
-                let mut rng = XorShiftRng::from_seed([42; 16]);
-                let original = $type::random_for_test(&mut rng);
-
-                let result = original.hash_tree_root();
-
-                assert_eq!(result.len(), 32);
-                // TODO: Add further tests
-                // https://github.com/sigp/lighthouse/issues/170
-            }
-        };
-    }
-
-    macro_rules! all_tests {
-        ($type: ident) => {
-            new_tests!($type);
-            math_between_tests!($type, $type);
-            math_tests!($type);
-            ssz_tests!($type);
-
-            mod u64_tests {
-                use super::*;
-
-                from_into_tests!($type, u64);
-                math_between_tests!($type, u64);
-
-                #[test]
-                pub fn as_64() {
-                    let x = $type(0).as_u64();
-                    assert_eq!(x, 0);
-
-                    let x = $type(3).as_u64();
-                    assert_eq!(x, 3);
-
-                    let x = $type(u64::max_value()).as_u64();
-                    assert_eq!(x, u64::max_value());
-                }
-            }
-
-            mod usize_tests {
-                use super::*;
-
-                from_into_tests!($type, usize);
-
-                #[test]
-                pub fn as_usize() {
-                    let x = $type(0).as_usize();
-                    assert_eq!(x, 0);
-
-                    let x = $type(3).as_usize();
-                    assert_eq!(x, 3);
-
-                    let x = $type(u64::max_value()).as_usize();
-                    assert_eq!(x, usize::max_value());
-                }
-            }
-        };
-    }
-
-    #[cfg(test)]
-    mod slot_tests {
-        use super::*;
-        use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
-        use ssz::ssz_encode;
-
-        all_tests!(Slot);
-    }
-
-    #[cfg(test)]
-    mod epoch_tests {
-        use super::*;
-        use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
-        use ssz::ssz_encode;
-
-        all_tests!(Epoch);
-    }
+    all_tests!(Slot);
+}
+
+#[cfg(test)]
+mod epoch_tests {
+    use super::*;
+    use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
+    use ssz::ssz_encode;
+
+    all_tests!(Epoch);
 }
diff --git a/eth2/types/src/slot_epoch_macros.rs b/eth2/types/src/slot_epoch_macros.rs
new file mode 100644
index 0000000000..48bc219da1
--- /dev/null
+++ b/eth2/types/src/slot_epoch_macros.rs
@@ -0,0 +1,621 @@
+macro_rules! impl_from_into_u64 {
+    ($main: ident) => {
+        impl From<u64> for $main {
+            fn from(n: u64) -> $main {
+                $main(n)
+            }
+        }
+
+        impl Into<u64> for $main {
+            fn into(self) -> u64 {
+                self.0
+            }
+        }
+
+        impl $main {
+            pub fn as_u64(&self) -> u64 {
+                self.0
+            }
+        }
+    };
+}
+
+// need to truncate for some fork-choice algorithms
+macro_rules! impl_into_u32 {
+    ($main: ident) => {
+        impl Into<u32> for $main {
+            fn into(self) -> u32 {
+                self.0 as u32
+            }
+        }
+
+        impl $main {
+            pub fn as_u32(&self) -> u32 {
+                self.0 as u32
+            }
+        }
+    };
+}
+
+macro_rules! impl_from_into_usize {
+    ($main: ident) => {
+        impl From<usize> for $main {
+            fn from(n: usize) -> $main {
+                $main(n as u64)
+            }
+        }
+
+        impl Into<usize> for $main {
+            fn into(self) -> usize {
+                self.0 as usize
+            }
+        }
+
+        impl $main {
+            pub fn as_usize(&self) -> usize {
+                self.0 as usize
+            }
+        }
+    };
+}
+
+macro_rules! impl_math_between {
+    ($main: ident, $other: ident) => {
+        impl PartialOrd<$other> for $main {
+            /// Utilizes `partial_cmp` on the underlying `u64`.
+            fn partial_cmp(&self, other: &$other) -> Option<Ordering> {
+                Some(self.0.cmp(&(*other).into()))
+            }
+        }
+
+        impl PartialEq<$other> for $main {
+            fn eq(&self, other: &$other) -> bool {
+                let other: u64 = (*other).into();
+                self.0 == other
+            }
+        }
+
+        impl Add<$other> for $main {
+            type Output = $main;
+
+            fn add(self, other: $other) -> $main {
+                $main::from(self.0.saturating_add(other.into()))
+            }
+        }
+
+        impl AddAssign<$other> for $main {
+            fn add_assign(&mut self, other: $other) {
+                self.0 = self.0.saturating_add(other.into());
+            }
+        }
+
+        impl Sub<$other> for $main {
+            type Output = $main;
+
+            fn sub(self, other: $other) -> $main {
+                $main::from(self.0.saturating_sub(other.into()))
+            }
+        }
+
+        impl SubAssign<$other> for $main {
+            fn sub_assign(&mut self, other: $other) {
+                self.0 = self.0.saturating_sub(other.into());
+            }
+        }
+
+        impl Mul<$other> for $main {
+            type Output = $main;
+
+            fn mul(self, rhs: $other) -> $main {
+                let rhs: u64 = rhs.into();
+                $main::from(self.0.saturating_mul(rhs))
+            }
+        }
+
+        impl MulAssign<$other> for $main {
+            fn mul_assign(&mut self, rhs: $other) {
+                let rhs: u64 = rhs.into();
+                self.0 = self.0.saturating_mul(rhs)
+            }
+        }
+
+        impl Div<$other> for $main {
+            type Output = $main;
+
+            fn div(self, rhs: $other) -> $main {
+                let rhs: u64 = rhs.into();
+                if rhs == 0 {
+                    panic!("Cannot divide by zero-valued Slot/Epoch")
+                }
+                $main::from(self.0 / rhs)
+            }
+        }
+
+        impl DivAssign<$other> for $main {
+            fn div_assign(&mut self, rhs: $other) {
+                let rhs: u64 = rhs.into();
+                if rhs == 0 {
+                    panic!("Cannot divide by zero-valued Slot/Epoch")
+                }
+                self.0 = self.0 / rhs
+            }
+        }
+
+        impl Rem<$other> for $main {
+            type Output = $main;
+
+            fn rem(self, modulus: $other) -> $main {
+                let modulus: u64 = modulus.into();
+                $main::from(self.0 % modulus)
+            }
+        }
+    };
+}
+
+macro_rules! impl_math {
+    ($type: ident) => {
+        impl $type {
+            pub fn saturating_sub<T: Into<$type>>(&self, other: T) -> $type {
+                *self - other.into()
+            }
+
+            pub fn saturating_add<T: Into<$type>>(&self, other: T) -> $type {
+                *self + other.into()
+            }
+
+            pub fn checked_div<T: Into<$type>>(&self, rhs: T) -> Option<$type> {
+                let rhs: $type = rhs.into();
+                if rhs == 0 {
+                    None
+                } else {
+                    Some(*self / rhs)
+                }
+            }
+
+            pub fn is_power_of_two(&self) -> bool {
+                self.0.is_power_of_two()
+            }
+        }
+
+        impl Ord for $type {
+            fn cmp(&self, other: &$type) -> Ordering {
+                let other: u64 = (*other).into();
+                self.0.cmp(&other)
+            }
+        }
+    };
+}
+
+macro_rules! impl_display {
+    ($type: ident) => {
+        impl fmt::Display for $type {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                write!(f, "{}", self.0)
+            }
+        }
+
+        impl slog::Value for $type {
+            fn serialize(
+                &self,
+                record: &slog::Record,
+                key: slog::Key,
+                serializer: &mut slog::Serializer,
+            ) -> slog::Result {
+                self.0.serialize(record, key, serializer)
+            }
+        }
+    };
+}
+
+macro_rules! impl_ssz {
+    ($type: ident) => {
+        impl Encodable for $type {
+            fn ssz_append(&self, s: &mut SszStream) {
+                s.append(&self.0);
+            }
+        }
+
+        impl Decodable for $type {
+            fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
+                let (value, i) = <_>::ssz_decode(bytes, i)?;
+
+                Ok(($type(value), i))
+            }
+        }
+
+        impl TreeHash for $type {
+            fn hash_tree_root(&self) -> Vec<u8> {
+                let mut result: Vec<u8> = vec![];
+                result.append(&mut self.0.hash_tree_root());
+                hash(&result)
+            }
+        }
+
+        impl<T: RngCore> TestRandom<T> for $type {
+            fn random_for_test(rng: &mut T) -> Self {
+                $type::from(u64::random_for_test(rng))
+            }
+        }
+    };
+}
+
+macro_rules! impl_hash {
+    ($type: ident) => {
+        // Implemented to stop clippy lint:
+        // https://rust-lang.github.io/rust-clippy/master/index.html#derive_hash_xor_eq
+        impl Hash for $type {
+            fn hash<H: Hasher>(&self, state: &mut H) {
+                ssz_encode(self).hash(state)
+            }
+        }
+    };
+}
+
+macro_rules! impl_common {
+    ($type: ident) => {
+        impl_from_into_u64!($type);
+        impl_from_into_usize!($type);
+        impl_math_between!($type, $type);
+        impl_math_between!($type, u64);
+        impl_math!($type);
+        impl_display!($type);
+        impl_ssz!($type);
+        impl_hash!($type);
+    };
+}
+
+// test macros
+#[allow(unused_macros)]
+macro_rules! new_tests {
+    ($type: ident) => {
+        #[test]
+        fn new() {
+            assert_eq!($type(0), $type::new(0));
+            assert_eq!($type(3), $type::new(3));
+            assert_eq!($type(u64::max_value()), $type::new(u64::max_value()));
+        }
+    };
+}
+
+#[allow(unused_macros)]
+macro_rules! from_into_tests {
+    ($type: ident, $other: ident) => {
+        #[test]
+        fn into() {
+            let x: $other = $type(0).into();
+            assert_eq!(x, 0);
+
+            let x: $other = $type(3).into();
+            assert_eq!(x, 3);
+
+            let x: $other = $type(u64::max_value()).into();
+            // Note: this will fail on 32 bit systems. This is expected as we don't have a proper
+            // 32-bit system strategy in place.
+            assert_eq!(x, $other::max_value());
+        }
+
+        #[test]
+        fn from() {
+            assert_eq!($type(0), $type::from(0_u64));
+            assert_eq!($type(3), $type::from(3_u64));
+            assert_eq!($type(u64::max_value()), $type::from($other::max_value()));
+        }
+    };
+}
+
+#[allow(unused_macros)]
+macro_rules! math_between_tests {
+    ($type: ident, $other: ident) => {
+        #[test]
+        fn partial_ord() {
+            let assert_partial_ord = |a: u64, partial_ord: Ordering, b: u64| {
+                let other: $other = $type(b).into();
+                assert_eq!($type(a).partial_cmp(&other), Some(partial_ord));
+            };
+
+            assert_partial_ord(1, Ordering::Less, 2);
+            assert_partial_ord(2, Ordering::Greater, 1);
+            assert_partial_ord(0, Ordering::Less, u64::max_value());
+            assert_partial_ord(u64::max_value(), Ordering::Greater, 0);
+        }
+
+        #[test]
+        fn partial_eq() {
+            let assert_partial_eq = |a: u64, b: u64, is_equal: bool| {
+                let other: $other = $type(b).into();
+                assert_eq!($type(a).eq(&other), is_equal);
+            };
+
+            assert_partial_eq(0, 0, true);
+            assert_partial_eq(0, 1, false);
+            assert_partial_eq(1, 0, false);
+            assert_partial_eq(1, 1, true);
+
+            assert_partial_eq(u64::max_value(), u64::max_value(), true);
+            assert_partial_eq(0, u64::max_value(), false);
+            assert_partial_eq(u64::max_value(), 0, false);
+        }
+
+        #[test]
+        fn add_and_add_assign() {
+            let assert_add = |a: u64, b: u64, result: u64| {
+                let other: $other = $type(b).into();
+                assert_eq!($type(a) + other, $type(result));
+
+                let mut add_assigned = $type(a);
+                add_assigned += other;
+
+                assert_eq!(add_assigned, $type(result));
+            };
+
+            assert_add(0, 1, 1);
+            assert_add(1, 0, 1);
+            assert_add(1, 2, 3);
+            assert_add(2, 1, 3);
+            assert_add(7, 7, 14);
+
+            // Addition should be saturating.
+            assert_add(u64::max_value(), 1, u64::max_value());
+            assert_add(u64::max_value(), u64::max_value(), u64::max_value());
+        }
+
+        #[test]
+        fn sub_and_sub_assign() {
+            let assert_sub = |a: u64, b: u64, result: u64| {
+                let other: $other = $type(b).into();
+                assert_eq!($type(a) - other, $type(result));
+
+                let mut sub_assigned = $type(a);
+                sub_assigned -= other;
+
+                assert_eq!(sub_assigned, $type(result));
+            };
+
+            assert_sub(1, 0, 1);
+            assert_sub(2, 1, 1);
+            assert_sub(14, 7, 7);
+            assert_sub(u64::max_value(), 1, u64::max_value() - 1);
+            assert_sub(u64::max_value(), u64::max_value(), 0);
+
+            // Subtraction should be saturating
+            assert_sub(0, 1, 0);
+            assert_sub(1, 2, 0);
+        }
+
+        #[test]
+        fn mul_and_mul_assign() {
+            let assert_mul = |a: u64, b: u64, result: u64| {
+                let other: $other = $type(b).into();
+                assert_eq!($type(a) * other, $type(result));
+
+                let mut mul_assigned = $type(a);
+                mul_assigned *= other;
+
+                assert_eq!(mul_assigned, $type(result));
+            };
+
+            assert_mul(2, 2, 4);
+            assert_mul(1, 2, 2);
+            assert_mul(0, 2, 0);
+
+            // Multiplication should be saturating.
+            assert_mul(u64::max_value(), 2, u64::max_value());
+        }
+
+        #[test]
+        fn div_and_div_assign() {
+            let assert_div = |a: u64, b: u64, result: u64| {
+                let other: $other = $type(b).into();
+                assert_eq!($type(a) / other, $type(result));
+
+                let mut div_assigned = $type(a);
+                div_assigned /= other;
+
+                assert_eq!(div_assigned, $type(result));
+            };
+
+            assert_div(0, 2, 0);
+            assert_div(2, 2, 1);
+            assert_div(100, 50, 2);
+            assert_div(128, 2, 64);
+            assert_div(u64::max_value(), 2, 2_u64.pow(63) - 1);
+        }
+
+        #[test]
+        #[should_panic]
+        fn div_panics_with_divide_by_zero() {
+            let other: $other = $type(0).into();
+            let _ = $type(2) / other;
+        }
+
+        #[test]
+        #[should_panic]
+        fn div_assign_panics_with_divide_by_zero() {
+            let other: $other = $type(0).into();
+            let mut assigned = $type(2);
+            assigned /= other;
+        }
+
+        #[test]
+        fn rem() {
+            let assert_rem = |a: u64, b: u64, result: u64| {
+                let other: $other = $type(b).into();
+                assert_eq!($type(a) % other, $type(result));
+            };
+
+            assert_rem(3, 2, 1);
+            assert_rem(40, 2, 0);
+            assert_rem(10, 100, 10);
+            assert_rem(302042, 3293, 2379);
+        }
+    };
+}
+
+#[allow(unused_macros)]
+macro_rules! math_tests {
+    ($type: ident) => {
+        #[test]
+        fn saturating_sub() {
+            let assert_saturating_sub = |a: u64, b: u64, result: u64| {
+                assert_eq!($type(a).saturating_sub($type(b)), $type(result));
+            };
+
+            assert_saturating_sub(1, 0, 1);
+            assert_saturating_sub(2, 1, 1);
+            assert_saturating_sub(14, 7, 7);
+            assert_saturating_sub(u64::max_value(), 1, u64::max_value() - 1);
+            assert_saturating_sub(u64::max_value(), u64::max_value(), 0);
+
+            // Subtraction should be saturating
+            assert_saturating_sub(0, 1, 0);
+            assert_saturating_sub(1, 2, 0);
+        }
+
+        #[test]
+        fn saturating_add() {
+            let assert_saturating_add = |a: u64, b: u64, result: u64| {
+                assert_eq!($type(a).saturating_add($type(b)), $type(result));
+            };
+
+            assert_saturating_add(0, 1, 1);
+            assert_saturating_add(1, 0, 1);
+            assert_saturating_add(1, 2, 3);
+            assert_saturating_add(2, 1, 3);
+            assert_saturating_add(7, 7, 14);
+
+            // Addition should be saturating.
+            assert_saturating_add(u64::max_value(), 1, u64::max_value());
+            assert_saturating_add(u64::max_value(), u64::max_value(), u64::max_value());
+        }
+
+        #[test]
+        fn checked_div() {
+            let assert_checked_div = |a: u64, b: u64, result: Option<u64>| {
+                let division_result_as_u64 = match $type(a).checked_div($type(b)) {
+                    None => None,
+                    Some(val) => Some(val.as_u64()),
+                };
+                assert_eq!(division_result_as_u64, result);
+            };
+
+            assert_checked_div(0, 2, Some(0));
+            assert_checked_div(2, 2, Some(1));
+            assert_checked_div(100, 50, Some(2));
+            assert_checked_div(128, 2, Some(64));
+            assert_checked_div(u64::max_value(), 2, Some(2_u64.pow(63) - 1));
+
+            assert_checked_div(2, 0, None);
+            assert_checked_div(0, 0, None);
+            assert_checked_div(u64::max_value(), 0, None);
+        }
+
+        #[test]
+        fn is_power_of_two() {
+            let assert_is_power_of_two = |a: u64, result: bool| {
+                assert_eq!(
+                    $type(a).is_power_of_two(),
+                    result,
+                    "{}.is_power_of_two() != {}",
+                    a,
+                    result
+                );
+            };
+
+            assert_is_power_of_two(0, false);
+            assert_is_power_of_two(1, true);
+            assert_is_power_of_two(2, true);
+            assert_is_power_of_two(3, false);
+            assert_is_power_of_two(4, true);
+
+            assert_is_power_of_two(2_u64.pow(4), true);
+            assert_is_power_of_two(u64::max_value(), false);
+        }
+
+        #[test]
+        fn ord() {
+            let assert_ord = |a: u64, ord: Ordering, b: u64| {
+                assert_eq!($type(a).cmp(&$type(b)), ord);
+            };
+
+            assert_ord(1, Ordering::Less, 2);
+            assert_ord(2, Ordering::Greater, 1);
+            assert_ord(0, Ordering::Less, u64::max_value());
+            assert_ord(u64::max_value(), Ordering::Greater, 0);
+        }
+    };
+}
+
+#[allow(unused_macros)]
+macro_rules! ssz_tests {
+    ($type: ident) => {
+        #[test]
+        pub fn test_ssz_round_trip() {
+            let mut rng = XorShiftRng::from_seed([42; 16]);
+            let original = $type::random_for_test(&mut rng);
+
+            let bytes = ssz_encode(&original);
+            let (decoded, _) = $type::ssz_decode(&bytes, 0).unwrap();
+
+            assert_eq!(original, decoded);
+        }
+
+        #[test]
+        pub fn test_hash_tree_root() {
+            let mut rng = XorShiftRng::from_seed([42; 16]);
+            let original = $type::random_for_test(&mut rng);
+
+            let result = original.hash_tree_root();
+
+            assert_eq!(result.len(), 32);
+            // TODO: Add further tests
+            // https://github.com/sigp/lighthouse/issues/170
+        }
+    };
+}
+
+#[allow(unused_macros)]
+macro_rules! all_tests {
+    ($type: ident) => {
+        new_tests!($type);
+        math_between_tests!($type, $type);
+        math_tests!($type);
+        ssz_tests!($type);
+
+        mod u64_tests {
+            use super::*;
+
+            from_into_tests!($type, u64);
+            math_between_tests!($type, u64);
+
+            #[test]
+            pub fn as_64() {
+                let x = $type(0).as_u64();
+                assert_eq!(x, 0);
+
+                let x = $type(3).as_u64();
+                assert_eq!(x, 3);
+
+                let x = $type(u64::max_value()).as_u64();
+                assert_eq!(x, u64::max_value());
+            }
+        }
+
+        mod usize_tests {
+            use super::*;
+
+            from_into_tests!($type, usize);
+
+            #[test]
+            pub fn as_usize() {
+                let x = $type(0).as_usize();
+                assert_eq!(x, 0);
+
+                let x = $type(3).as_usize();
+                assert_eq!(x, 3);
+
+                let x = $type(u64::max_value()).as_usize();
+                assert_eq!(x, usize::max_value());
+            }
+        }
+    };
+}
diff --git a/eth2/types/src/slot_height.rs b/eth2/types/src/slot_height.rs
index 77dd17ad96..afa0ff775a 100644
--- a/eth2/types/src/slot_height.rs
+++ b/eth2/types/src/slot_height.rs
@@ -1,290 +1,13 @@
-// Copyright 2019 Sigma Prime Pty Ltd.
-//
-// Permission is hereby granted, free of charge, to any person obtaining a
-// copy of this software and associated documentation files (the "Software"),
-// to deal in the Software without restriction, including without limitation
-// the rights to use, copy, modify, merge, publish, distribute, sublicense,
-// and/or sell copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in
-// all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
-// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-// DEALINGS IN THE SOFTWARE.
-
 use crate::slot_epoch::{Epoch, Slot};
+use crate::test_utils::TestRandom;
+use rand::RngCore;
 use serde_derive::Serialize;
-use slog;
 use ssz::{hash, ssz_encode, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use std::cmp::{Ord, Ordering};
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Rem, Sub, SubAssign};
 
-macro_rules! impl_from_into_u64 {
-    ($main: ident) => {
-        impl From<u64> for $main {
-            fn from(n: u64) -> $main {
-                $main(n)
-            }
-        }
-
-        impl Into<u64> for $main {
-            fn into(self) -> u64 {
-                self.0
-            }
-        }
-
-        impl $main {
-            pub fn as_u64(&self) -> u64 {
-                self.0
-            }
-        }
-    };
-}
-
-// need to truncate for some fork-choice algorithms
-macro_rules! impl_into_u32 {
-    ($main: ident) => {
-        impl Into<u32> for $main {
-            fn into(self) -> u32 {
-                self.0 as u32
-            }
-        }
-
-        impl $main {
-            pub fn as_u32(&self) -> u32 {
-                self.0 as u32
-            }
-        }
-    };
-}
-macro_rules! impl_from_into_usize {
-    ($main: ident) => {
-        impl From<usize> for $main {
-            fn from(n: usize) -> $main {
-                $main(n as u64)
-            }
-        }
-
-        impl Into<usize> for $main {
-            fn into(self) -> usize {
-                self.0 as usize
-            }
-        }
-
-        impl $main {
-            pub fn as_usize(&self) -> usize {
-                self.0 as usize
-            }
-        }
-    };
-}
-
-macro_rules! impl_math_between {
-    ($main: ident, $other: ident) => {
-        impl PartialOrd<$other> for $main {
-            /// Utilizes `partial_cmp` on the underlying `u64`.
-            fn partial_cmp(&self, other: &$other) -> Option<Ordering> {
-                Some(self.0.cmp(&(*other).into()))
-            }
-        }
-
-        impl PartialEq<$other> for $main {
-            fn eq(&self, other: &$other) -> bool {
-                let other: u64 = (*other).into();
-                self.0 == other
-            }
-        }
-
-        impl Add<$other> for $main {
-            type Output = $main;
-
-            fn add(self, other: $other) -> $main {
-                $main::from(self.0.saturating_add(other.into()))
-            }
-        }
-
-        impl AddAssign<$other> for $main {
-            fn add_assign(&mut self, other: $other) {
-                self.0 = self.0.saturating_add(other.into());
-            }
-        }
-
-        impl Sub<$other> for $main {
-            type Output = $main;
-
-            fn sub(self, other: $other) -> $main {
-                $main::from(self.0.saturating_sub(other.into()))
-            }
-        }
-
-        impl SubAssign<$other> for $main {
-            fn sub_assign(&mut self, other: $other) {
-                self.0 = self.0.saturating_sub(other.into());
-            }
-        }
-
-        impl Mul<$other> for $main {
-            type Output = $main;
-
-            fn mul(self, rhs: $other) -> $main {
-                let rhs: u64 = rhs.into();
-                $main::from(self.0.saturating_mul(rhs))
-            }
-        }
-
-        impl MulAssign<$other> for $main {
-            fn mul_assign(&mut self, rhs: $other) {
-                let rhs: u64 = rhs.into();
-                self.0 = self.0.saturating_mul(rhs)
-            }
-        }
-
-        impl Div<$other> for $main {
-            type Output = $main;
-
-            fn div(self, rhs: $other) -> $main {
-                let rhs: u64 = rhs.into();
-                if rhs == 0 {
-                    panic!("Cannot divide by zero-valued Slot/Epoch")
-                }
-                $main::from(self.0 / rhs)
-            }
-        }
-
-        impl DivAssign<$other> for $main {
-            fn div_assign(&mut self, rhs: $other) {
-                let rhs: u64 = rhs.into();
-                if rhs == 0 {
-                    panic!("Cannot divide by zero-valued Slot/Epoch")
-                }
-                self.0 = self.0 / rhs
-            }
-        }
-
-        impl Rem<$other> for $main {
-            type Output = $main;
-
-            fn rem(self, modulus: $other) -> $main {
-                let modulus: u64 = modulus.into();
-                $main::from(self.0 % modulus)
-            }
-        }
-    };
-}
-
-macro_rules! impl_math {
-    ($type: ident) => {
-        impl $type {
-            pub fn saturating_sub<T: Into<$type>>(&self, other: T) -> $type {
-                *self - other.into()
-            }
-
-            pub fn saturating_add<T: Into<$type>>(&self, other: T) -> $type {
-                *self + other.into()
-            }
-
-            pub fn checked_div<T: Into<$type>>(&self, rhs: T) -> Option<$type> {
-                let rhs: $type = rhs.into();
-                if rhs == 0 {
-                    None
-                } else {
-                    Some(*self / rhs)
-                }
-            }
-
-            pub fn is_power_of_two(&self) -> bool {
-                self.0.is_power_of_two()
-            }
-        }
-
-        impl Ord for $type {
-            fn cmp(&self, other: &$type) -> Ordering {
-                let other: u64 = (*other).into();
-                self.0.cmp(&other)
-            }
-        }
-    };
-}
-
-macro_rules! impl_display {
-    ($type: ident) => {
-        impl fmt::Display for $type {
-            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-                write!(f, "{}", self.0)
-            }
-        }
-
-        impl slog::Value for $type {
-            fn serialize(
-                &self,
-                record: &slog::Record,
-                key: slog::Key,
-                serializer: &mut slog::Serializer,
-            ) -> slog::Result {
-                self.0.serialize(record, key, serializer)
-            }
-        }
-    };
-}
-
-macro_rules! impl_ssz {
-    ($type: ident) => {
-        impl Encodable for $type {
-            fn ssz_append(&self, s: &mut SszStream) {
-                s.append(&self.0);
-            }
-        }
-
-        impl Decodable for $type {
-            fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-                let (value, i) = <_>::ssz_decode(bytes, i)?;
-
-                Ok(($type(value), i))
-            }
-        }
-
-        impl TreeHash for $type {
-            fn hash_tree_root(&self) -> Vec<u8> {
-                let mut result: Vec<u8> = vec![];
-                result.append(&mut self.0.hash_tree_root());
-                hash(&result)
-            }
-        }
-    };
-}
-
-macro_rules! impl_hash {
-    ($type: ident) => {
-        // Implemented to stop clippy lint:
-        // https://rust-lang.github.io/rust-clippy/master/index.html#derive_hash_xor_eq
-        impl Hash for $type {
-            fn hash<H: Hasher>(&self, state: &mut H) {
-                ssz_encode(self).hash(state)
-            }
-        }
-    };
-}
-
-macro_rules! impl_common {
-    ($type: ident) => {
-        impl_from_into_u64!($type);
-        impl_from_into_usize!($type);
-        impl_math_between!($type, $type);
-        impl_math_between!($type, u64);
-        impl_math!($type);
-        impl_display!($type);
-        impl_ssz!($type);
-        impl_hash!($type);
-    };
-}
 /// Beacon block height, effectively `Slot/GENESIS_START_BLOCK`.
 #[derive(Eq, Debug, Clone, Copy, Default, Serialize)]
 pub struct SlotHeight(u64);
@@ -309,3 +32,13 @@ impl SlotHeight {
         SlotHeight(u64::max_value())
     }
 }
+
+#[cfg(test)]
+
+mod slot_height_tests {
+    use super::*;
+    use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
+    use ssz::ssz_encode;
+
+    all_tests!(SlotHeight);
+}
diff --git a/eth2/types/src/spec/mod.rs b/eth2/types/src/spec/mod.rs
deleted file mode 100644
index 53c78a2c2c..0000000000
--- a/eth2/types/src/spec/mod.rs
+++ /dev/null
@@ -1,92 +0,0 @@
-mod foundation;
-
-use crate::{Address, Epoch, Hash256, Slot};
-use bls::Signature;
-
-/// Holds all the "constants" for a BeaconChain.
-///
-/// Spec v0.2.0
-#[derive(PartialEq, Debug, Clone)]
-pub struct ChainSpec {
-    /*
-     * Misc
-     */
-    pub shard_count: u64,
-    pub target_committee_size: u64,
-    pub max_balance_churn_quotient: u64,
-    pub beacon_chain_shard_number: u64,
-    pub max_indices_per_slashable_vote: u64,
-    pub max_withdrawals_per_epoch: u64,
-    pub shuffle_round_count: u64,
-
-    /*
-     *  Deposit contract
-     */
-    pub deposit_contract_address: Address,
-    pub deposit_contract_tree_depth: u64,
-
-    /*
-     *  Gwei values
-     */
-    pub min_deposit_amount: u64,
-    pub max_deposit_amount: u64,
-    pub fork_choice_balance_increment: u64,
-    pub ejection_balance: u64,
-
-    /*
-     * Initial Values
-     */
-    pub genesis_fork_version: u64,
-    pub genesis_slot: Slot,
-    pub genesis_epoch: Epoch,
-    pub genesis_start_shard: u64,
-    pub far_future_epoch: Epoch,
-    pub zero_hash: Hash256,
-    pub empty_signature: Signature,
-    pub bls_withdrawal_prefix_byte: u8,
-
-    /*
-     * Time parameters
-     */
-    pub slot_duration: u64,
-    pub min_attestation_inclusion_delay: u64,
-    pub epoch_length: u64,
-    pub seed_lookahead: Epoch,
-    pub entry_exit_delay: u64,
-    pub eth1_data_voting_period: u64,
-    pub min_validator_withdrawal_epochs: Epoch,
-
-    /*
-     * State list lengths
-     */
-    pub latest_block_roots_length: usize,
-    pub latest_randao_mixes_length: usize,
-    pub latest_index_roots_length: usize,
-    pub latest_penalized_exit_length: usize,
-
-    /*
-     * Reward and penalty quotients
-     */
-    pub base_reward_quotient: u64,
-    pub whistleblower_reward_quotient: u64,
-    pub includer_reward_quotient: u64,
-    pub inactivity_penalty_quotient: u64,
-
-    /*
-     * Max operations per block
-     */
-    pub max_proposer_slashings: u64,
-    pub max_attester_slashings: u64,
-    pub max_attestations: u64,
-    pub max_deposits: u64,
-    pub max_exits: u64,
-
-    /*
-     * Signature domains
-     */
-    pub domain_deposit: u64,
-    pub domain_attestation: u64,
-    pub domain_proposal: u64,
-    pub domain_exit: u64,
-    pub domain_randao: u64,
-}
diff --git a/eth2/utils/vec_shuffle/Cargo.toml b/eth2/utils/fisher_yates_shuffle/Cargo.toml
similarity index 85%
rename from eth2/utils/vec_shuffle/Cargo.toml
rename to eth2/utils/fisher_yates_shuffle/Cargo.toml
index aaeb50074d..7d33c2e91a 100644
--- a/eth2/utils/vec_shuffle/Cargo.toml
+++ b/eth2/utils/fisher_yates_shuffle/Cargo.toml
@@ -1,5 +1,5 @@
 [package]
-name = "vec_shuffle"
+name = "fisher_yates_shuffle"
 version = "0.1.0"
 authors = ["Paul Hauner <paul@paulhauner.com>"]
 edition = "2018"
diff --git a/eth2/utils/vec_shuffle/src/lib.rs b/eth2/utils/fisher_yates_shuffle/src/lib.rs
similarity index 100%
rename from eth2/utils/vec_shuffle/src/lib.rs
rename to eth2/utils/fisher_yates_shuffle/src/lib.rs
diff --git a/eth2/utils/vec_shuffle/src/rng.rs b/eth2/utils/fisher_yates_shuffle/src/rng.rs
similarity index 100%
rename from eth2/utils/vec_shuffle/src/rng.rs
rename to eth2/utils/fisher_yates_shuffle/src/rng.rs
diff --git a/eth2/utils/vec_shuffle/src/specs/shuffle_test_vectors.yaml b/eth2/utils/fisher_yates_shuffle/src/specs/shuffle_test_vectors.yaml
similarity index 100%
rename from eth2/utils/vec_shuffle/src/specs/shuffle_test_vectors.yaml
rename to eth2/utils/fisher_yates_shuffle/src/specs/shuffle_test_vectors.yaml
diff --git a/eth2/utils/int_to_bytes/Cargo.toml b/eth2/utils/int_to_bytes/Cargo.toml
new file mode 100644
index 0000000000..f7424e0328
--- /dev/null
+++ b/eth2/utils/int_to_bytes/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "int_to_bytes"
+version = "0.1.0"
+authors = ["Paul Hauner <paul@paulhauner.com>"]
+edition = "2018"
+
+[dependencies]
+bytes = "0.4"
+
+[dev-dependencies]
+yaml-rust = "0.4.2"
+hex = "0.3"
diff --git a/eth2/utils/int_to_bytes/src/lib.rs b/eth2/utils/int_to_bytes/src/lib.rs
new file mode 100644
index 0000000000..537d7b5c84
--- /dev/null
+++ b/eth2/utils/int_to_bytes/src/lib.rs
@@ -0,0 +1,125 @@
+use bytes::{BufMut, BytesMut};
+
+/// Returns `int` as little-endian bytes with a length of 1.
+pub fn int_to_bytes1(int: u8) -> Vec<u8> {
+    vec![int]
+}
+
+/// Returns `int` as little-endian bytes with a length of 2.
+pub fn int_to_bytes2(int: u16) -> Vec<u8> {
+    let mut bytes = BytesMut::with_capacity(2);
+    bytes.put_u16_le(int);
+    bytes.to_vec()
+}
+
+/// Returns `int` as little-endian bytes with a length of 3.
+///
+/// An `Option` is returned as Rust does not support a native
+/// `u24` type.
+///
+/// The Eth 2.0 specification uses `int.to_bytes(2, 'little')`, which throws an error if `int`
+/// doesn't fit within 3 bytes. The specification relies upon implicit asserts for some validity
+/// conditions, so we ensure the calling function is aware of the error condition as opposed to
+/// hiding it with a modulo.
+pub fn int_to_bytes3(int: u32) -> Option<Vec<u8>> {
+    if int < 2_u32.pow(3 * 8) {
+        let mut bytes = BytesMut::with_capacity(4);
+        bytes.put_u32_le(int);
+        Some(bytes[0..3].to_vec())
+    } else {
+        None
+    }
+}
+
+/// Returns `int` as little-endian bytes with a length of 4.
+pub fn int_to_bytes4(int: u32) -> Vec<u8> {
+    let mut bytes = BytesMut::with_capacity(4);
+    bytes.put_u32_le(int);
+    bytes.to_vec()
+}
+
+/// Returns `int` as little-endian bytes with a length of 8.
+pub fn int_to_bytes8(int: u64) -> Vec<u8> {
+    let mut bytes = BytesMut::with_capacity(8);
+    bytes.put_u64_le(int);
+    bytes.to_vec()
+}
+
+/// Returns `int` as little-endian bytes with a length of 32.
+pub fn int_to_bytes32(int: u64) -> Vec<u8> {
+    let mut bytes = BytesMut::with_capacity(32);
+    bytes.put_u64_le(int);
+    bytes.resize(32, 0);
+    bytes.to_vec()
+}
+
+/// Returns `int` as little-endian bytes with a length of 48.
+pub fn int_to_bytes48(int: u64) -> Vec<u8> {
+    let mut bytes = BytesMut::with_capacity(48);
+    bytes.put_u64_le(int);
+    bytes.resize(48, 0);
+    bytes.to_vec()
+}
+
+/// Returns `int` as little-endian bytes with a length of 96.
+pub fn int_to_bytes96(int: u64) -> Vec<u8> {
+    let mut bytes = BytesMut::with_capacity(96);
+    bytes.put_u64_le(int);
+    bytes.resize(96, 0);
+    bytes.to_vec()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use hex;
+    use std::{fs::File, io::prelude::*, path::PathBuf};
+    use yaml_rust::yaml;
+
+    #[test]
+    fn int_to_bytes3_returns_none() {
+        assert_eq!(int_to_bytes3(2_u32.pow(24)), None);
+    }
+
+    #[test]
+    fn test_vectors() {
+        /*
+         * Test vectors are generated here:
+         *
+         * https://github.com/ethereum/eth2.0-test-generators
+         */
+        let mut file = {
+            let mut file_path_buf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+            file_path_buf.push("src/specs/test_vector_int_to_bytes.yml");
+
+            File::open(file_path_buf).unwrap()
+        };
+
+        let mut yaml_str = String::new();
+
+        file.read_to_string(&mut yaml_str).unwrap();
+
+        let docs = yaml::YamlLoader::load_from_str(&yaml_str).unwrap();
+        let doc = &docs[0];
+        let test_cases = doc["test_cases"].as_vec().unwrap();
+
+        for test_case in test_cases {
+            let byte_length = test_case["byte_length"].as_i64().unwrap() as u64;
+            let int = test_case["int"].as_i64().unwrap() as u64;
+            let bytes_string = test_case["bytes"].clone().into_string().unwrap();
+            let bytes = hex::decode(bytes_string.replace("0x", "")).unwrap();
+
+            match byte_length {
+                1 => assert_eq!(int_to_bytes1(int as u8), bytes),
+                2 => assert_eq!(int_to_bytes2(int as u16), bytes),
+                3 => assert_eq!(int_to_bytes3(int as u32), Some(bytes)),
+                4 => assert_eq!(int_to_bytes4(int as u32), bytes),
+                8 => assert_eq!(int_to_bytes8(int), bytes),
+                32 => assert_eq!(int_to_bytes32(int), bytes),
+                48 => assert_eq!(int_to_bytes48(int), bytes),
+                96 => assert_eq!(int_to_bytes96(int), bytes),
+                _ => panic!("Unknown byte length in test vector."),
+            }
+        }
+    }
+}
diff --git a/eth2/utils/int_to_bytes/src/specs/test_vector_int_to_bytes.yml b/eth2/utils/int_to_bytes/src/specs/test_vector_int_to_bytes.yml
new file mode 100644
index 0000000000..3b7eaa9c10
--- /dev/null
+++ b/eth2/utils/int_to_bytes/src/specs/test_vector_int_to_bytes.yml
@@ -0,0 +1,215 @@
+fork: tchaikovsky
+summary: Test vectors for the `int_to_bytes[n]` functions.`
+test_suite: int_to_bytes
+title: int_to_bytes Tests
+version: 1.0
+test_cases:
+- {byte_length: 1, bytes: '0x00', int: 0}
+- {byte_length: 1, bytes: '0x01', int: 1}
+- {byte_length: 1, bytes: '0xff', int: 255}
+- {byte_length: 1, bytes: '0xc0', int: 192}
+- {byte_length: 1, bytes: '0xc7', int: 199}
+- {byte_length: 1, bytes: '0xf2', int: 242}
+- {byte_length: 1, bytes: '0x26', int: 38}
+- {byte_length: 1, bytes: '0xfb', int: 251}
+- {byte_length: 1, bytes: '0xd5', int: 213}
+- {byte_length: 1, bytes: '0x74', int: 116}
+- {byte_length: 1, bytes: '0xa8', int: 168}
+- {byte_length: 1, bytes: '0xc6', int: 198}
+- {byte_length: 1, bytes: '0x3d', int: 61}
+- {byte_length: 1, bytes: '0xc2', int: 194}
+- {byte_length: 1, bytes: '0x68', int: 104}
+- {byte_length: 1, bytes: '0x64', int: 100}
+- {byte_length: 1, bytes: '0xc2', int: 194}
+- {byte_length: 1, bytes: '0x78', int: 120}
+- {byte_length: 1, bytes: '0x33', int: 51}
+- {byte_length: 2, bytes: '0x0000', int: 0}
+- {byte_length: 2, bytes: '0x0100', int: 1}
+- {byte_length: 2, bytes: '0xffff', int: 65535}
+- {byte_length: 2, bytes: '0xedea', int: 60141}
+- {byte_length: 2, bytes: '0x2d93', int: 37677}
+- {byte_length: 2, bytes: '0x611e', int: 7777}
+- {byte_length: 2, bytes: '0x637c', int: 31843}
+- {byte_length: 2, bytes: '0xe370', int: 28899}
+- {byte_length: 2, bytes: '0x96b3', int: 45974}
+- {byte_length: 2, bytes: '0xde44', int: 17630}
+- {byte_length: 2, bytes: '0xa009', int: 2464}
+- {byte_length: 2, bytes: '0xf6ba', int: 47862}
+- {byte_length: 2, bytes: '0xef76', int: 30447}
+- {byte_length: 2, bytes: '0x7e5f', int: 24446}
+- {byte_length: 2, bytes: '0x393d', int: 15673}
+- {byte_length: 2, bytes: '0xc820', int: 8392}
+- {byte_length: 2, bytes: '0x9031', int: 12688}
+- {byte_length: 2, bytes: '0x3963', int: 25401}
+- {byte_length: 2, bytes: '0x033d', int: 15619}
+- {byte_length: 3, bytes: '0x000000', int: 0}
+- {byte_length: 3, bytes: '0x010000', int: 1}
+- {byte_length: 3, bytes: '0xffffff', int: 16777215}
+- {byte_length: 3, bytes: '0x1fdfb2', int: 11722527}
+- {byte_length: 3, bytes: '0x2a7504', int: 292138}
+- {byte_length: 3, bytes: '0x09fb20', int: 2161417}
+- {byte_length: 3, bytes: '0xa4a6b2', int: 11708068}
+- {byte_length: 3, bytes: '0x17feb7', int: 12058135}
+- {byte_length: 3, bytes: '0x3ad0b1', int: 11653178}
+- {byte_length: 3, bytes: '0xbc92c6', int: 13013692}
+- {byte_length: 3, bytes: '0xb6c046', int: 4636854}
+- {byte_length: 3, bytes: '0x937f00', int: 32659}
+- {byte_length: 3, bytes: '0x8266cb', int: 13330050}
+- {byte_length: 3, bytes: '0x8136e9', int: 15283841}
+- {byte_length: 3, bytes: '0xe9e062', int: 6480105}
+- {byte_length: 3, bytes: '0x50d054', int: 5558352}
+- {byte_length: 3, bytes: '0xb95340', int: 4215737}
+- {byte_length: 3, bytes: '0x779f52', int: 5414775}
+- {byte_length: 3, bytes: '0x15aed0', int: 13676053}
+- {byte_length: 4, bytes: '0x00000000', int: 0}
+- {byte_length: 4, bytes: '0x01000000', int: 1}
+- {byte_length: 4, bytes: '0xffffffff', int: 4294967295}
+- {byte_length: 4, bytes: '0x389cd0ca', int: 3402669112}
+- {byte_length: 4, bytes: '0xfb29dc70', int: 1893476859}
+- {byte_length: 4, bytes: '0xf5f5c999', int: 2580149749}
+- {byte_length: 4, bytes: '0xf4f0b8d1', int: 3518558452}
+- {byte_length: 4, bytes: '0x830de883', int: 2213023107}
+- {byte_length: 4, bytes: '0xe3b4e843', int: 1139324131}
+- {byte_length: 4, bytes: '0x4c9ce594', int: 2498075724}
+- {byte_length: 4, bytes: '0xa9826dab', int: 2876080809}
+- {byte_length: 4, bytes: '0xc40aecb7', int: 3085699780}
+- {byte_length: 4, bytes: '0x55490416', int: 369379669}
+- {byte_length: 4, bytes: '0x4f2eedc5', int: 3320655439}
+- {byte_length: 4, bytes: '0xdd07257e', int: 2116356061}
+- {byte_length: 4, bytes: '0x481a57e9', int: 3914799688}
+- {byte_length: 4, bytes: '0x4556a493', int: 2477020741}
+- {byte_length: 4, bytes: '0xccb781ed', int: 3984701388}
+- {byte_length: 4, bytes: '0x6b994065', int: 1698732395}
+- {byte_length: 8, bytes: '0x0000000000000000', int: 0}
+- {byte_length: 8, bytes: '0x0100000000000000', int: 1}
+- {byte_length: 8, bytes: '0xffffffff00000000', int: 4294967295}
+- {byte_length: 8, bytes: '0x77d6e31400000000', int: 350475895}
+- {byte_length: 8, bytes: '0xf3e681bf00000000', int: 3212961523}
+- {byte_length: 8, bytes: '0x62fa7bd800000000', int: 3632003682}
+- {byte_length: 8, bytes: '0x82c67b4500000000', int: 1165739650}
+- {byte_length: 8, bytes: '0x52577fba00000000', int: 3128907602}
+- {byte_length: 8, bytes: '0x5eac939b00000000', int: 2610146398}
+- {byte_length: 8, bytes: '0x12ba143700000000', int: 924105234}
+- {byte_length: 8, bytes: '0x1d3b893a00000000', int: 982072093}
+- {byte_length: 8, bytes: '0x8262153000000000', int: 806707842}
+- {byte_length: 8, bytes: '0xbb9cc58e00000000', int: 2395315387}
+- {byte_length: 8, bytes: '0x76fef6d100000000', int: 3522625142}
+- {byte_length: 8, bytes: '0x0fc3d35700000000', int: 1473495823}
+- {byte_length: 8, bytes: '0xc7f851de00000000', int: 3729914055}
+- {byte_length: 8, bytes: '0x3a1e5cb200000000', int: 2992381498}
+- {byte_length: 8, bytes: '0x3b748e3400000000', int: 881751099}
+- {byte_length: 8, bytes: '0xdc92479600000000', int: 2521273052}
+- {byte_length: 32, bytes: '0x0000000000000000000000000000000000000000000000000000000000000000',
+  int: 0}
+- {byte_length: 32, bytes: '0x0100000000000000000000000000000000000000000000000000000000000000',
+  int: 1}
+- {byte_length: 32, bytes: '0xffffffff00000000000000000000000000000000000000000000000000000000',
+  int: 4294967295}
+- {byte_length: 32, bytes: '0x2395ad4c00000000000000000000000000000000000000000000000000000000',
+  int: 1286444323}
+- {byte_length: 32, bytes: '0x38a735b800000000000000000000000000000000000000000000000000000000',
+  int: 3090523960}
+- {byte_length: 32, bytes: '0x5a9416e100000000000000000000000000000000000000000000000000000000',
+  int: 3776353370}
+- {byte_length: 32, bytes: '0x220f757500000000000000000000000000000000000000000000000000000000',
+  int: 1970605858}
+- {byte_length: 32, bytes: '0x65bf635200000000000000000000000000000000000000000000000000000000',
+  int: 1382268773}
+- {byte_length: 32, bytes: '0x033f902200000000000000000000000000000000000000000000000000000000',
+  int: 579878659}
+- {byte_length: 32, bytes: '0x2b2d58ab00000000000000000000000000000000000000000000000000000000',
+  int: 2874682667}
+- {byte_length: 32, bytes: '0x15af31da00000000000000000000000000000000000000000000000000000000',
+  int: 3660689173}
+- {byte_length: 32, bytes: '0xd260642e00000000000000000000000000000000000000000000000000000000',
+  int: 778330322}
+- {byte_length: 32, bytes: '0xcdf8429700000000000000000000000000000000000000000000000000000000',
+  int: 2537748685}
+- {byte_length: 32, bytes: '0xc9304b0500000000000000000000000000000000000000000000000000000000',
+  int: 88813769}
+- {byte_length: 32, bytes: '0xf7b7ba0200000000000000000000000000000000000000000000000000000000',
+  int: 45791223}
+- {byte_length: 32, bytes: '0x1ee262d900000000000000000000000000000000000000000000000000000000',
+  int: 3647136286}
+- {byte_length: 32, bytes: '0xb34b03d300000000000000000000000000000000000000000000000000000000',
+  int: 3540208563}
+- {byte_length: 32, bytes: '0x3d52db4d00000000000000000000000000000000000000000000000000000000',
+  int: 1306219069}
+- {byte_length: 32, bytes: '0xd86db47900000000000000000000000000000000000000000000000000000000',
+  int: 2041867736}
+- {byte_length: 48, bytes: '0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 0}
+- {byte_length: 48, bytes: '0x010000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1}
+- {byte_length: 48, bytes: '0xffffffff0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 4294967295}
+- {byte_length: 48, bytes: '0x61aeae650000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1705946721}
+- {byte_length: 48, bytes: '0xd1c08fac0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 2895102161}
+- {byte_length: 48, bytes: '0x6f36b6c90000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3384161903}
+- {byte_length: 48, bytes: '0x102f2f3b0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 992947984}
+- {byte_length: 48, bytes: '0x0f53f9240000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 620319503}
+- {byte_length: 48, bytes: '0x5c1d46b30000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3007716700}
+- {byte_length: 48, bytes: '0x955791510000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1368479637}
+- {byte_length: 48, bytes: '0xf934170f0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 253179129}
+- {byte_length: 48, bytes: '0xc1a8b76f0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1874307265}
+- {byte_length: 48, bytes: '0xdf3f62c20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3261218783}
+- {byte_length: 48, bytes: '0xbd741bc50000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3306910909}
+- {byte_length: 48, bytes: '0xfe5dc5540000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1422220798}
+- {byte_length: 48, bytes: '0x364f10df0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3742388022}
+- {byte_length: 48, bytes: '0x4a3909450000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1158232394}
+- {byte_length: 48, bytes: '0xe04760380000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 945833952}
+- {byte_length: 48, bytes: '0x755c78540000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1417174133}
+- {byte_length: 96, bytes: '0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 0}
+- {byte_length: 96, bytes: '0x010000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1}
+- {byte_length: 96, bytes: '0xffffffff0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 4294967295}
+- {byte_length: 96, bytes: '0xa3274ee20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3796772771}
+- {byte_length: 96, bytes: '0x1658135c0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1544771606}
+- {byte_length: 96, bytes: '0x2af24fb30000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3008361002}
+- {byte_length: 96, bytes: '0x9e6bc40a0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 180644766}
+- {byte_length: 96, bytes: '0x0745b3c50000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3316860167}
+- {byte_length: 96, bytes: '0xe1b59f830000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 2208282081}
+- {byte_length: 96, bytes: '0x985a9e6e0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1855871640}
+- {byte_length: 96, bytes: '0x3d4e3a090000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 154816061}
+- {byte_length: 96, bytes: '0x6f5dfb630000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1677417839}
+- {byte_length: 96, bytes: '0x383cdecd0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3453893688}
+- {byte_length: 96, bytes: '0x38f55ceb0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3948737848}
+- {byte_length: 96, bytes: '0xcd746f5d0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1567585485}
+- {byte_length: 96, bytes: '0x3d971e910000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 2434701117}
+- {byte_length: 96, bytes: '0x3adff0c00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3237011258}
+- {byte_length: 96, bytes: '0x5ed40a710000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 1896535134}
+- {byte_length: 96, bytes: '0x755d2ed40000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
+  int: 3559808373}
diff --git a/eth2/utils/swap_or_not_shuffle/Cargo.toml b/eth2/utils/swap_or_not_shuffle/Cargo.toml
new file mode 100644
index 0000000000..272abf6084
--- /dev/null
+++ b/eth2/utils/swap_or_not_shuffle/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "swap_or_not_shuffle"
+version = "0.1.0"
+authors = ["Paul Hauner <paul@paulhauner.com>"]
+edition = "2018"
+
+[dependencies]
+bytes = "0.4"
+hashing = { path = "../hashing" }
+int_to_bytes = { path = "../int_to_bytes" }
+
+[dev-dependencies]
+yaml-rust = "0.4.2"
+hex = "0.3"
+ethereum-types = "0.5"
diff --git a/eth2/utils/swap_or_not_shuffle/src/lib.rs b/eth2/utils/swap_or_not_shuffle/src/lib.rs
new file mode 100644
index 0000000000..753265f3e7
--- /dev/null
+++ b/eth2/utils/swap_or_not_shuffle/src/lib.rs
@@ -0,0 +1,178 @@
+use bytes::Buf;
+use hashing::hash;
+use int_to_bytes::{int_to_bytes1, int_to_bytes4};
+use std::cmp::max;
+use std::io::Cursor;
+
+/// Return `p(index)` in a pseudorandom permutation `p` of `0...list_size-1` with ``seed`` as entropy.
+///
+/// Utilizes 'swap or not' shuffling found in
+/// https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf
+/// See the 'generalized domain' algorithm on page 3.
+///
+/// Returns `None` under any of the following conditions:
+///  - `list_size == 0`
+///  - `index >= list_size`
+///  - `list_size > 2**24`
+///  - `list_size > usize::max_value() / 2`
+pub fn get_permutated_index(
+    index: usize,
+    list_size: usize,
+    seed: &[u8],
+    shuffle_round_count: u8,
+) -> Option<usize> {
+    if list_size == 0
+        || index >= list_size
+        || list_size > usize::max_value() / 2
+        || list_size > 2_usize.pow(24)
+    {
+        return None;
+    }
+
+    let mut index = index;
+    for round in 0..shuffle_round_count {
+        let pivot = bytes_to_int64(&hash_with_round(seed, round)[..]) as usize % list_size;
+        let flip = (pivot + list_size - index) % list_size;
+        let position = max(index, flip);
+        let source = hash_with_round_and_position(seed, round, position)?;
+        let byte = source[(position % 256) / 8];
+        let bit = (byte >> (position % 8)) % 2;
+        index = if bit == 1 { flip } else { index }
+    }
+    Some(index)
+}
+
+fn hash_with_round_and_position(seed: &[u8], round: u8, position: usize) -> Option<Vec<u8>> {
+    let mut seed = seed.to_vec();
+    seed.append(&mut int_to_bytes1(round));
+    /*
+     * Note: the specification has an implicit assertion in `int_to_bytes4` that `position / 256 <
+     * 2**24`. For efficiency, we do not check for that here as it is checked in `get_permutated_index`.
+     */
+    seed.append(&mut int_to_bytes4((position / 256) as u32));
+    Some(hash(&seed[..]))
+}
+
+fn hash_with_round(seed: &[u8], round: u8) -> Vec<u8> {
+    let mut seed = seed.to_vec();
+    seed.append(&mut int_to_bytes1(round));
+    hash(&seed[..])
+}
+
+fn bytes_to_int64(bytes: &[u8]) -> u64 {
+    let mut cursor = Cursor::new(bytes);
+    cursor.get_u64_le()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ethereum_types::H256 as Hash256;
+    use hex;
+    use std::{fs::File, io::prelude::*, path::PathBuf};
+    use yaml_rust::yaml;
+
+    #[test]
+    #[ignore]
+    fn fuzz_test() {
+        let max_list_size = 2_usize.pow(24);
+        let test_runs = 1000;
+
+        // Test at max list_size with the end index.
+        for _ in 0..test_runs {
+            let index = max_list_size - 1;
+            let list_size = max_list_size;
+            let seed = Hash256::random();
+            let shuffle_rounds = 90;
+
+            assert!(get_permutated_index(index, list_size, &seed[..], shuffle_rounds).is_some());
+        }
+
+        // Test at max list_size low indices.
+        for i in 0..test_runs {
+            let index = i;
+            let list_size = max_list_size;
+            let seed = Hash256::random();
+            let shuffle_rounds = 90;
+
+            assert!(get_permutated_index(index, list_size, &seed[..], shuffle_rounds).is_some());
+        }
+
+        // Test at max list_size high indices.
+        for i in 0..test_runs {
+            let index = max_list_size - 1 - i;
+            let list_size = max_list_size;
+            let seed = Hash256::random();
+            let shuffle_rounds = 90;
+
+            assert!(get_permutated_index(index, list_size, &seed[..], shuffle_rounds).is_some());
+        }
+    }
+
+    #[test]
+    fn returns_none_for_zero_length_list() {
+        assert_eq!(None, get_permutated_index(100, 0, &[42, 42], 90));
+    }
+
+    #[test]
+    fn returns_none_for_out_of_bounds_index() {
+        assert_eq!(None, get_permutated_index(100, 100, &[42, 42], 90));
+    }
+
+    #[test]
+    fn returns_none_for_too_large_list() {
+        assert_eq!(
+            None,
+            get_permutated_index(100, usize::max_value() / 2, &[42, 42], 90)
+        );
+    }
+
+    #[test]
+    fn test_vectors() {
+        /*
+         * Test vectors are generated here:
+         *
+         * https://github.com/ethereum/eth2.0-test-generators
+         */
+        let mut file = {
+            let mut file_path_buf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+            file_path_buf.push("src/specs/test_vector_permutated_index.yml");
+
+            File::open(file_path_buf).unwrap()
+        };
+
+        let mut yaml_str = String::new();
+
+        file.read_to_string(&mut yaml_str).unwrap();
+
+        let docs = yaml::YamlLoader::load_from_str(&yaml_str).unwrap();
+        let doc = &docs[0];
+        let test_cases = doc["test_cases"].as_vec().unwrap();
+
+        for (i, test_case) in test_cases.iter().enumerate() {
+            let index = test_case["index"].as_i64().unwrap() as usize;
+            let list_size = test_case["list_size"].as_i64().unwrap() as usize;
+            let permutated_index = test_case["permutated_index"].as_i64().unwrap() as usize;
+            let shuffle_round_count = test_case["shuffle_round_count"].as_i64().unwrap();
+            let seed_string = test_case["seed"].clone().into_string().unwrap();
+            let seed = hex::decode(seed_string.replace("0x", "")).unwrap();
+
+            let shuffle_round_count = if shuffle_round_count < (u8::max_value() as i64) {
+                shuffle_round_count as u8
+            } else {
+                panic!("shuffle_round_count must be a u8")
+            };
+
+            assert_eq!(
+                Some(permutated_index),
+                get_permutated_index(index, list_size, &seed[..], shuffle_round_count),
+                "Failure on case #{} index: {}, list_size: {}, round_count: {}, seed: {}",
+                i,
+                index,
+                list_size,
+                shuffle_round_count,
+                seed_string,
+            );
+        }
+    }
+}
diff --git a/eth2/utils/swap_or_not_shuffle/src/specs/test_vector_permutated_index.yml b/eth2/utils/swap_or_not_shuffle/src/specs/test_vector_permutated_index.yml
new file mode 100644
index 0000000000..61b117fa92
--- /dev/null
+++ b/eth2/utils/swap_or_not_shuffle/src/specs/test_vector_permutated_index.yml
@@ -0,0 +1,86 @@
+fork: tchaikovsky
+summary: Test vectors for list shuffling using `get_permutated_index`
+test_suite: permutated_index
+title: Permutated Index Tests
+version: 1.0
+test_cases:
+- {index: 0, list_size: 1, permutated_index: 0, seed: '0xc0c7f226fbd574a8c63dc26864c27833ea931e7c70b34409ba765f3d2031633d',
+  shuffle_round_count: 90}
+- {index: 0, list_size: 2, permutated_index: 0, seed: '0xb20420b2b7b1c64600cbe962544052d0bbe13da403950d198d4f4ea28762953f',
+  shuffle_round_count: 90}
+- {index: 1, list_size: 2, permutated_index: 0, seed: '0x11f1322c3a4cfce20efb7d7eca50291470043d6e8a2c62956e687571607d3f0e',
+  shuffle_round_count: 90}
+- {index: 0, list_size: 3, permutated_index: 2, seed: '0x5bd0af3f74fe6986bb99b3ecc0ea15a403456ce708c05ceeeddc0a4205caf072',
+  shuffle_round_count: 90}
+- {index: 1, list_size: 3, permutated_index: 1, seed: '0xba06ff9bde03f37eddeacb261a51109676d549c1bea3b81edd82df68cc03a97f',
+  shuffle_round_count: 90}
+- {index: 2, list_size: 3, permutated_index: 2, seed: '0xf58a8970c63ca86dd3b8b8a615302ec06cddea1279bf4a2725c781ce6aba348d',
+  shuffle_round_count: 90}
+- {index: 0, list_size: 1024, permutated_index: 1005, seed: '0x383556e23fcb9e73c23ad33cfb50f4c098f49688a84b128c2885960e5f1b3982',
+  shuffle_round_count: 90}
+- {index: 1023, list_size: 1024, permutated_index: 934, seed: '0x2ee5dab30ad1580cdabb175a4b1512cac5566866d65a15e9e22c8444f460c9dc',
+  shuffle_round_count: 90}
+- {index: 3925, list_size: 4040, permutated_index: 32, seed: '0x34a3c13f211e63c56e9e1187f31a56a4230d8d5bf5e584f0e4fe93946af91cce',
+  shuffle_round_count: 90}
+- {index: 885, list_size: 2417, permutated_index: 1822, seed: '0x1346e3970815107154b58b1eff411bfca3342ea0d8282a86304d79d62d5f3c52',
+  shuffle_round_count: 90}
+- {index: 840, list_size: 1805, permutated_index: 808, seed: '0x0810c104b75e25bf89c0066deebc3461937fc0e72ae04ee74f245616c15718df',
+  shuffle_round_count: 90}
+- {index: 881, list_size: 1788, permutated_index: 582, seed: '0x34adb35f3fc2880d220e520120a032bbaa0f4bd7a5fcf1c2269de21075e7a464',
+  shuffle_round_count: 90}
+- {index: 1362, list_size: 1817, permutated_index: 1018, seed: '0xc9b0c76e11f4c3c3c38b447aca5352d93132ad5678da420ca2e69d92588e0fba',
+  shuffle_round_count: 90}
+- {index: 28, list_size: 111, permutated_index: 0, seed: '0x293145c31aeb3eb29ccdf3327d0f3dd4592cdfb2fad3703229c6c2e720dc792f',
+  shuffle_round_count: 90}
+- {index: 959, list_size: 2558, permutated_index: 2094, seed: '0xc9f4c5fbb2a397fd8ea36dbfcec0d733d0af7ec3a03d789a66231f3bc7cafa5e',
+  shuffle_round_count: 90}
+- {index: 887, list_size: 2406, permutated_index: 831, seed: '0x565729e0d5de524e6dee54d1b8b5882ad8e55c18a30462ac02c4bb86c27d26cb',
+  shuffle_round_count: 90}
+- {index: 3526, list_size: 3674, permutated_index: 3531, seed: '0x2951395b1a1bbda8d53b776c7fc8bdad6030de943c4e3f938202ac553f44381d',
+  shuffle_round_count: 90}
+- {index: 978, list_size: 3175, permutated_index: 2257, seed: '0x74aac23523cb45b7ee52d5d2f7b2d24ebc6bf2d63ef189efccabc4a16bb17cd8',
+  shuffle_round_count: 90}
+- {index: 37, list_size: 231, permutated_index: 48, seed: '0xe4083e61b31931bad662392758e8bc30a4ce7b26b6897c2221a3358f25fdc1d8',
+  shuffle_round_count: 90}
+- {index: 340, list_size: 693, permutated_index: 234, seed: '0x8089c1f242aa48c6611180f221c120e930adeecaf3084b2b85f9b1dfebe34f63',
+  shuffle_round_count: 90}
+- {index: 0, list_size: 9, permutated_index: 1, seed: '0x7fda0ab6a746b6b0206febb8259891e0e6f88bf52143b20d6c78caf7caf8e7b3',
+  shuffle_round_count: 90}
+- {index: 200, list_size: 1108, permutated_index: 952, seed: '0x87b210d000b5f57e9834388d4bc2b86ae8b31383fa10a34b029546c2ebabb807',
+  shuffle_round_count: 90}
+- {index: 1408, list_size: 1531, permutated_index: 584, seed: '0x0670a78b38e0419aaead5d1cc8f40f58044b7076ced8193c08b580dd95a13555',
+  shuffle_round_count: 90}
+- {index: 1704, list_size: 1863, permutated_index: 1022, seed: '0xdbf78665190a6133191e91ab35b1106e8984dfc0dfa36018004f880b431c2a14',
+  shuffle_round_count: 90}
+- {index: 793, list_size: 3938, permutated_index: 2607, seed: '0x54bf0192292ffae0bf39b39f12e0540b97591af0a2980d32f277bd33201395d3',
+  shuffle_round_count: 90}
+- {index: 14, list_size: 28, permutated_index: 10, seed: '0x43054417c6056404c586c907dfc5fceb66ebef541d143b00a3b676f3c0fbf4c5',
+  shuffle_round_count: 90}
+- {index: 2909, list_size: 3920, permutated_index: 726, seed: '0x5eabf289fdcfe0a3aba33a185fb1a4ae2f2b6f78daf61f5d356971e0cb270207',
+  shuffle_round_count: 90}
+- {index: 1943, list_size: 1959, permutated_index: 1292, seed: '0xca86322db56927d727101e31c93f616f746317d29aa10d88f371592963de92aa',
+  shuffle_round_count: 90}
+- {index: 1647, list_size: 2094, permutated_index: 1805, seed: '0x3cfe274230a112bc68614882645339fda2f134501a042079d620ec65cf8d3fa6',
+  shuffle_round_count: 90}
+- {index: 1012, list_size: 1877, permutated_index: 216, seed: '0x7b5ff8a848af32d85c6d37c26e61a57e96780fcebc350ad1845e83fe5e4679ac',
+  shuffle_round_count: 90}
+- {index: 35, list_size: 2081, permutated_index: 1458, seed: '0x40691aa31a49c2391e025ec272c812510cb07c055f6201e84479499326330628',
+  shuffle_round_count: 90}
+- {index: 1136, list_size: 2189, permutated_index: 1579, seed: '0x31a0deb2c8c5f809f413b7a36ec680ee8b19bbb9a39c4e207326155864bc8be5',
+  shuffle_round_count: 90}
+- {index: 1775, list_size: 3434, permutated_index: 707, seed: '0x92f30d8556382b72a5797db811486e7a213e0145d6c946e5121aa6a8f761d164',
+  shuffle_round_count: 90}
+- {index: 1109, list_size: 2010, permutated_index: 433, seed: '0x093fb976f2497361897012dfa6dc019009eda2e48bbeb4b7c56d4aa5da7d5f87',
+  shuffle_round_count: 90}
+- {index: 359, list_size: 538, permutated_index: 115, seed: '0xa79b35beacbe48c662d60884c704040024c55ab879e5f61521013c5f45eb3b70',
+  shuffle_round_count: 90}
+- {index: 1259, list_size: 1473, permutated_index: 1351, seed: '0x02c53c9c6ddf259716ff02e49a294eba33e4ad255d7e90dbefdbc991adf603e5',
+  shuffle_round_count: 90}
+- {index: 2087, list_size: 2634, permutated_index: 1497, seed: '0xa5a4c57c5705ec697a74e6c7161191b18f58ca882a0fcc18f68dc3b57a1aa5b6',
+  shuffle_round_count: 90}
+- {index: 2069, list_size: 2511, permutated_index: 1837, seed: '0xe7051ebc07f2e7b4d4b28f48d1e42d7b9dcec31c240ca6e1a0c06139ccfc4b8f',
+  shuffle_round_count: 90}
+- {index: 1660, list_size: 3932, permutated_index: 3046, seed: '0x8687c029ffc443879527a64c31b7acbb38ab6e343779d0b2c6e250046fdb9de8',
+  shuffle_round_count: 90}
+- {index: 379, list_size: 646, permutated_index: 32, seed: '0x17e854f4e80401345e13f72af45b221c9f7a840f6a8c1328ddf9c9ca9a088379',
+  shuffle_round_count: 90}