diff --git a/beacon_node/beacon_chain/src/attestation_aggregator.rs b/beacon_node/beacon_chain/src/attestation_aggregator.rs
index 70348dc945..54f178068d 100644
--- a/beacon_node/beacon_chain/src/attestation_aggregator.rs
+++ b/beacon_node/beacon_chain/src/attestation_aggregator.rs
@@ -129,10 +129,13 @@ impl AttestationAggregator {
             Some(validator_record) => validator_record,
         };
 
-        if !free_attestation
-            .signature
-            .verify(&signable_message, &validator_record.pubkey)
-        {
+        if !free_attestation.signature.verify(
+            &signable_message,
+            cached_state
+                .fork
+                .get_domain(cached_state.current_epoch(spec), spec.domain_attestation),
+            &validator_record.pubkey,
+        ) {
             invalid_outcome!(Message::BadSignature);
         }
 
diff --git a/beacon_node/beacon_chain/test_harness/src/validator_harness/local_signer.rs b/beacon_node/beacon_chain/test_harness/src/validator_harness/local_signer.rs
index aa46a1c9a4..3f249cb199 100644
--- a/beacon_node/beacon_chain/test_harness/src/validator_harness/local_signer.rs
+++ b/beacon_node/beacon_chain/test_harness/src/validator_harness/local_signer.rs
@@ -25,23 +25,23 @@ impl LocalSigner {
     }
 
     /// Sign some message.
-    fn bls_sign(&self, message: &[u8]) -> Option<Signature> {
-        Some(Signature::new(message, &self.keypair.sk))
+    fn bls_sign(&self, message: &[u8], domain: u64) -> Option<Signature> {
+        Some(Signature::new(message, domain, &self.keypair.sk))
     }
 }
 
 impl BlockProposerSigner for LocalSigner {
-    fn sign_block_proposal(&self, message: &[u8]) -> Option<Signature> {
-        self.bls_sign(message)
+    fn sign_block_proposal(&self, message: &[u8], domain: u64) -> Option<Signature> {
+        self.bls_sign(message, domain)
     }
 
-    fn sign_randao_reveal(&self, message: &[u8]) -> Option<Signature> {
-        self.bls_sign(message)
+    fn sign_randao_reveal(&self, message: &[u8], domain: u64) -> Option<Signature> {
+        self.bls_sign(message, domain)
     }
 }
 
 impl AttesterSigner for LocalSigner {
-    fn sign_attestation_message(&self, message: &[u8]) -> Option<Signature> {
-        self.bls_sign(message)
+    fn sign_attestation_message(&self, message: &[u8], domain: u64) -> Option<Signature> {
+        self.bls_sign(message, domain)
     }
 }
diff --git a/eth2/attester/src/lib.rs b/eth2/attester/src/lib.rs
index 7352dd2ea8..13a1d72bb9 100644
--- a/eth2/attester/src/lib.rs
+++ b/eth2/attester/src/lib.rs
@@ -10,6 +10,7 @@ pub use self::traits::{
 };
 
 const PHASE_0_CUSTODY_BIT: bool = false;
+const DOMAIN_ATTESTATION: u64 = 1;
 
 #[derive(Debug, PartialEq)]
 pub enum PollOutcome {
@@ -136,8 +137,10 @@ impl<T: SlotClock, U: BeaconNode, V: DutiesReader, W: Signer> Attester<T, U, V,
     fn sign_attestation_data(&mut self, attestation_data: &AttestationData) -> Option<Signature> {
         self.store_produce(attestation_data);
 
-        self.signer
-            .sign_attestation_message(&attestation_data.signable_message(PHASE_0_CUSTODY_BIT)[..])
+        self.signer.sign_attestation_message(
+            &attestation_data.signable_message(PHASE_0_CUSTODY_BIT)[..],
+            DOMAIN_ATTESTATION,
+        )
     }
 
     /// Returns `true` if signing some attestation_data is safe (non-slashable).
diff --git a/eth2/attester/src/test_utils/local_signer.rs b/eth2/attester/src/test_utils/local_signer.rs
index c256d10506..896d907752 100644
--- a/eth2/attester/src/test_utils/local_signer.rs
+++ b/eth2/attester/src/test_utils/local_signer.rs
@@ -25,7 +25,7 @@ impl LocalSigner {
 }
 
 impl Signer for LocalSigner {
-    fn sign_attestation_message(&self, message: &[u8]) -> Option<Signature> {
-        Some(Signature::new(message, &self.keypair.sk))
+    fn sign_attestation_message(&self, message: &[u8], domain: u64) -> Option<Signature> {
+        Some(Signature::new(message, domain, &self.keypair.sk))
     }
 }
diff --git a/eth2/attester/src/traits.rs b/eth2/attester/src/traits.rs
index 53bce3aaa7..6062460cb1 100644
--- a/eth2/attester/src/traits.rs
+++ b/eth2/attester/src/traits.rs
@@ -45,5 +45,5 @@ pub trait DutiesReader: Send + Sync {
 
 /// Signs message using an internally-maintained private key.
 pub trait Signer {
-    fn sign_attestation_message(&self, message: &[u8]) -> Option<Signature>;
+    fn sign_attestation_message(&self, message: &[u8], domain: u64) -> Option<Signature>;
 }
diff --git a/eth2/block_proposer/src/lib.rs b/eth2/block_proposer/src/lib.rs
index cf71edd99f..0e66bdc70a 100644
--- a/eth2/block_proposer/src/lib.rs
+++ b/eth2/block_proposer/src/lib.rs
@@ -134,7 +134,10 @@ impl<T: SlotClock, U: BeaconNode, V: DutiesReader, W: Signer> BlockProducer<T, U
             // TODO: add domain, etc to this message. Also ensure result matches `into_to_bytes32`.
             let message = int_to_bytes32(slot.epoch(self.spec.epoch_length).as_u64());
 
-            match self.signer.sign_randao_reveal(&message) {
+            match self
+                .signer
+                .sign_randao_reveal(&message, self.spec.domain_randao)
+            {
                 None => return Ok(PollOutcome::SignerRejection(slot)),
                 Some(signature) => signature,
             }
@@ -166,10 +169,10 @@ impl<T: SlotClock, U: BeaconNode, V: DutiesReader, W: Signer> BlockProducer<T, U
     fn sign_block(&mut self, mut block: BeaconBlock) -> Option<BeaconBlock> {
         self.store_produce(&block);
 
-        match self
-            .signer
-            .sign_block_proposal(&block.proposal_root(&self.spec)[..])
-        {
+        match self.signer.sign_block_proposal(
+            &block.proposal_root(&self.spec)[..],
+            self.spec.domain_proposal,
+        ) {
             None => None,
             Some(signature) => {
                 block.signature = signature;
diff --git a/eth2/block_proposer/src/test_utils/local_signer.rs b/eth2/block_proposer/src/test_utils/local_signer.rs
index 0ebefa29d6..d7f490c300 100644
--- a/eth2/block_proposer/src/test_utils/local_signer.rs
+++ b/eth2/block_proposer/src/test_utils/local_signer.rs
@@ -25,11 +25,11 @@ impl LocalSigner {
 }
 
 impl Signer for LocalSigner {
-    fn sign_block_proposal(&self, message: &[u8]) -> Option<Signature> {
-        Some(Signature::new(message, &self.keypair.sk))
+    fn sign_block_proposal(&self, message: &[u8], domain: u64) -> Option<Signature> {
+        Some(Signature::new(message, domain, &self.keypair.sk))
     }
 
-    fn sign_randao_reveal(&self, message: &[u8]) -> Option<Signature> {
-        Some(Signature::new(message, &self.keypair.sk))
+    fn sign_randao_reveal(&self, message: &[u8], domain: u64) -> Option<Signature> {
+        Some(Signature::new(message, domain, &self.keypair.sk))
     }
 }
diff --git a/eth2/block_proposer/src/traits.rs b/eth2/block_proposer/src/traits.rs
index 5eb27bce71..c6e57d833f 100644
--- a/eth2/block_proposer/src/traits.rs
+++ b/eth2/block_proposer/src/traits.rs
@@ -44,6 +44,6 @@ pub trait DutiesReader: Send + Sync {
 
 /// Signs message using an internally-maintained private key.
 pub trait Signer {
-    fn sign_block_proposal(&self, message: &[u8]) -> Option<Signature>;
-    fn sign_randao_reveal(&self, message: &[u8]) -> Option<Signature>;
+    fn sign_block_proposal(&self, message: &[u8], domain: u64) -> Option<Signature>;
+    fn sign_randao_reveal(&self, message: &[u8], domain: u64) -> Option<Signature>;
 }
diff --git a/eth2/fork_choice/src/protolambda_lmd_ghost.rs b/eth2/fork_choice/src/protolambda_lmd_ghost.rs
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/eth2/fork_choice/src/protolambda_lmd_ghost.rs
@@ -0,0 +1 @@
+
diff --git a/eth2/state_processing/src/block_processable.rs b/eth2/state_processing/src/block_processable.rs
index 0e6b57cf08..effaa65079 100644
--- a/eth2/state_processing/src/block_processable.rs
+++ b/eth2/state_processing/src/block_processable.rs
@@ -396,14 +396,12 @@ fn validate_attestation_signature_optional(
     Ok(())
 }
 
-fn get_domain(_fork: &Fork, _epoch: Epoch, _domain_type: u64) -> u64 {
-    // TODO: stubbed out.
-    0
+fn get_domain(fork: &Fork, epoch: Epoch, domain_type: u64) -> u64 {
+    fork.get_domain(epoch, domain_type)
 }
 
-fn bls_verify(pubkey: &PublicKey, message: &[u8], signature: &Signature, _domain: u64) -> bool {
-    // TODO: add domain
-    signature.verify(message, pubkey)
+fn bls_verify(pubkey: &PublicKey, message: &[u8], signature: &Signature, domain: u64) -> bool {
+    signature.verify(message, domain, pubkey)
 }
 
 impl From<AttestationValidationError> for Error {
diff --git a/eth2/types/src/attestation.rs b/eth2/types/src/attestation.rs
index 66140decbc..73a587c26b 100644
--- a/eth2/types/src/attestation.rs
+++ b/eth2/types/src/attestation.rs
@@ -26,11 +26,13 @@ impl Attestation {
         &self,
         group_public_key: &AggregatePublicKey,
         custody_bit: bool,
-        // TODO: use domain.
-        _domain: u64,
+        domain: u64,
     ) -> bool {
-        self.aggregate_signature
-            .verify(&self.signable_message(custody_bit), group_public_key)
+        self.aggregate_signature.verify(
+            &self.signable_message(custody_bit),
+            domain,
+            group_public_key,
+        )
     }
 }
 
diff --git a/eth2/types/src/beacon_state.rs b/eth2/types/src/beacon_state.rs
index 0270bb87c6..85b49bf01c 100644
--- a/eth2/types/src/beacon_state.rs
+++ b/eth2/types/src/beacon_state.rs
@@ -2,8 +2,8 @@ use self::epoch_cache::EpochCache;
 use crate::test_utils::TestRandom;
 use crate::{
     validator::StatusFlags, validator_registry::get_active_validator_indices, AttestationData,
-    Bitfield, ChainSpec, Crosslink, Deposit, DepositData, Epoch, Eth1Data, Eth1DataVote, Fork,
-    Hash256, PendingAttestation, PublicKey, Signature, Slot, Validator,
+    Bitfield, ChainSpec, Crosslink, Deposit, DepositData, DepositInput, Epoch, Eth1Data,
+    Eth1DataVote, Fork, Hash256, PendingAttestation, PublicKey, Signature, Slot, Validator,
 };
 use bls::verify_proof_of_possession;
 use honey_badger_split::SplitExt;
@@ -515,6 +515,7 @@ impl BeaconState {
         &self,
         slot: Slot,
         registry_change: bool,
+
         spec: &ChainSpec,
     ) -> Result<Vec<Vec<usize>>, Error> {
         let (_committees_per_epoch, seed, shuffling_epoch, _shuffling_start_shard) =
@@ -792,6 +793,30 @@ impl BeaconState {
         self.validator_registry_update_epoch = current_epoch;
     }
 
+    /// Confirm validator owns PublicKey
+    ///
+    /// Spec v0.2.0
+    pub fn validate_proof_of_possession(
+        &self,
+        pubkey: PublicKey,
+        proof_of_possession: Signature,
+        withdrawal_credentials: Hash256,
+        spec: &ChainSpec,
+    ) -> bool {
+        let proof_of_possession_data = DepositInput {
+            pubkey: pubkey.clone(),
+            withdrawal_credentials,
+            proof_of_possession: Signature::empty_signature(),
+        };
+
+        proof_of_possession.verify(
+            &proof_of_possession_data.hash_tree_root(),
+            self.fork
+                .get_domain(self.slot.epoch(spec.epoch_length), spec.domain_deposit),
+            &pubkey,
+        )
+    }
+
     /// Process multiple deposits in sequence.
     ///
     /// Builds a hashmap of validator pubkeys to validator index and passes it to each successive
@@ -843,8 +868,17 @@ impl BeaconState {
         pubkey_map: Option<&HashMap<PublicKey, usize>>,
         spec: &ChainSpec,
     ) -> Result<usize, ()> {
-        // TODO: ensure verify proof-of-possession represents the spec accurately.
-        if !verify_proof_of_possession(&proof_of_possession, &pubkey) {
+        // TODO: update proof of possession to function written above (
+        // requires bls::create_proof_of_possession to be updated
+        // https://github.com/sigp/lighthouse/issues/239
+        if !verify_proof_of_possession(&proof_of_possession, &pubkey)
+        //if !self.validate_proof_of_possession(
+        //    pubkey.clone(),
+        //    proof_of_possession,
+        //    withdrawal_credentials,
+        //    &spec,
+        //    )
+        {
             return Err(());
         }
 
diff --git a/eth2/types/src/fork.rs b/eth2/types/src/fork.rs
index 35285d6ed9..bf168f03f4 100644
--- a/eth2/types/src/fork.rs
+++ b/eth2/types/src/fork.rs
@@ -10,6 +10,22 @@ pub struct Fork {
     pub epoch: Epoch,
 }
 
+impl Fork {
+    /// Return the fork version of the given ``epoch``.
+    pub fn get_fork_version(&self, epoch: Epoch) -> u64 {
+        if epoch < self.epoch {
+            return self.previous_version;
+        }
+        self.current_version
+    }
+
+    /// Get the domain number that represents the fork meta and signature domain.
+    pub fn get_domain(&self, epoch: Epoch, domain_type: u64) -> u64 {
+        let fork_version = self.get_fork_version(epoch);
+        fork_version * u64::pow(2, 32) + domain_type
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Fork {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
diff --git a/eth2/types/src/test_utils/signature.rs b/eth2/types/src/test_utils/signature.rs
index 9ec7aec60a..d9995835ac 100644
--- a/eth2/types/src/test_utils/signature.rs
+++ b/eth2/types/src/test_utils/signature.rs
@@ -8,6 +8,6 @@ impl<T: RngCore> TestRandom<T> for Signature {
         let mut message = vec![0; 32];
         rng.fill_bytes(&mut message);
 
-        Signature::new(&message, &secret_key)
+        Signature::new(&message, 0, &secret_key)
     }
 }
diff --git a/eth2/utils/bls/Cargo.toml b/eth2/utils/bls/Cargo.toml
index 465510c591..7a436307b5 100644
--- a/eth2/utils/bls/Cargo.toml
+++ b/eth2/utils/bls/Cargo.toml
@@ -5,7 +5,7 @@ authors = ["Paul Hauner <paul@paulhauner.com>"]
 edition = "2018"
 
 [dependencies]
-bls-aggregates = { git = "https://github.com/sigp/signature-schemes", tag = "v0.3.0" }
+bls-aggregates = { git = "https://github.com/sigp/signature-schemes", tag = "0.5.2" }
 hashing = { path = "../hashing" }
 hex = "0.3"
 serde = "1.0"
diff --git a/eth2/utils/bls/src/aggregate_signature.rs b/eth2/utils/bls/src/aggregate_signature.rs
index b606a5ebd3..4ee79d0aa8 100644
--- a/eth2/utils/bls/src/aggregate_signature.rs
+++ b/eth2/utils/bls/src/aggregate_signature.rs
@@ -27,8 +27,13 @@ impl AggregateSignature {
     ///
     /// Only returns `true` if the set of keys in the `AggregatePublicKey` match the set of keys
     /// that signed the `AggregateSignature`.
-    pub fn verify(&self, msg: &[u8], aggregate_public_key: &AggregatePublicKey) -> bool {
-        self.0.verify(msg, aggregate_public_key)
+    pub fn verify(
+        &self,
+        msg: &[u8],
+        domain: u64,
+        aggregate_public_key: &AggregatePublicKey,
+    ) -> bool {
+        self.0.verify(msg, domain, aggregate_public_key)
     }
 }
 
@@ -73,7 +78,7 @@ mod tests {
         let keypair = Keypair::random();
 
         let mut original = AggregateSignature::new();
-        original.add(&Signature::new(&[42, 42], &keypair.sk));
+        original.add(&Signature::new(&[42, 42], 0, &keypair.sk));
 
         let bytes = ssz_encode(&original);
         let (decoded, _) = AggregateSignature::ssz_decode(&bytes, 0).unwrap();
diff --git a/eth2/utils/bls/src/lib.rs b/eth2/utils/bls/src/lib.rs
index 646047d183..8f2e9fac03 100644
--- a/eth2/utils/bls/src/lib.rs
+++ b/eth2/utils/bls/src/lib.rs
@@ -1,5 +1,4 @@
 extern crate bls_aggregates;
-extern crate hashing;
 extern crate ssz;
 
 mod aggregate_signature;
@@ -16,37 +15,29 @@ pub use crate::signature::Signature;
 
 pub use self::bls_aggregates::AggregatePublicKey;
 
-pub const BLS_AGG_SIG_BYTE_SIZE: usize = 97;
+pub const BLS_AGG_SIG_BYTE_SIZE: usize = 96;
 
-use hashing::hash;
 use ssz::ssz_encode;
-use std::default::Default;
-
-fn extend_if_needed(hash: &mut Vec<u8>) {
-    // NOTE: bls_aggregates crate demands 48 bytes, this may be removed as we get closer to production
-    hash.resize(48, Default::default())
-}
 
 /// For some signature and public key, ensure that the signature message was the public key and it
 /// was signed by the secret key that corresponds to that public key.
 pub fn verify_proof_of_possession(sig: &Signature, pubkey: &PublicKey) -> bool {
-    let mut hash = hash(&ssz_encode(pubkey));
-    extend_if_needed(&mut hash);
-    sig.verify_hashed(&hash, &pubkey)
+    // TODO: replace this function with state.validate_proof_of_possession
+    // https://github.com/sigp/lighthouse/issues/239
+    sig.verify(&ssz_encode(pubkey), 0, &pubkey)
 }
 
+// TODO: Update this method
+// https://github.com/sigp/lighthouse/issues/239
 pub fn create_proof_of_possession(keypair: &Keypair) -> Signature {
-    let mut hash = hash(&ssz_encode(&keypair.pk));
-    extend_if_needed(&mut hash);
-    Signature::new_hashed(&hash, &keypair.sk)
+    Signature::new(&ssz_encode(&keypair.pk), 0, &keypair.sk)
 }
 
 pub fn bls_verify_aggregate(
     pubkey: &AggregatePublicKey,
     message: &[u8],
     signature: &AggregateSignature,
-    _domain: u64,
+    domain: u64,
 ) -> bool {
-    // TODO: add domain
-    signature.verify(message, pubkey)
+    signature.verify(message, domain, pubkey)
 }
diff --git a/eth2/utils/bls/src/signature.rs b/eth2/utils/bls/src/signature.rs
index 511681957c..c0c31ef27b 100644
--- a/eth2/utils/bls/src/signature.rs
+++ b/eth2/utils/bls/src/signature.rs
@@ -14,24 +14,34 @@ pub struct Signature(RawSignature);
 
 impl Signature {
     /// Instantiate a new Signature from a message and a SecretKey.
-    pub fn new(msg: &[u8], sk: &SecretKey) -> Self {
-        Signature(RawSignature::new(msg, sk.as_raw()))
+    pub fn new(msg: &[u8], domain: u64, sk: &SecretKey) -> Self {
+        Signature(RawSignature::new(msg, domain, sk.as_raw()))
     }
 
     /// Instantiate a new Signature from a message and a SecretKey, where the message has already
     /// been hashed.
-    pub fn new_hashed(msg_hashed: &[u8], sk: &SecretKey) -> Self {
-        Signature(RawSignature::new_hashed(msg_hashed, sk.as_raw()))
+    pub fn new_hashed(x_real_hashed: &[u8], x_imaginary_hashed: &[u8], sk: &SecretKey) -> Self {
+        Signature(RawSignature::new_hashed(
+            x_real_hashed,
+            x_imaginary_hashed,
+            sk.as_raw(),
+        ))
     }
 
     /// Verify the Signature against a PublicKey.
-    pub fn verify(&self, msg: &[u8], pk: &PublicKey) -> bool {
-        self.0.verify(msg, pk.as_raw())
+    pub fn verify(&self, msg: &[u8], domain: u64, pk: &PublicKey) -> bool {
+        self.0.verify(msg, domain, pk.as_raw())
     }
 
     /// Verify the Signature against a PublicKey, where the message has already been hashed.
-    pub fn verify_hashed(&self, msg_hash: &[u8], pk: &PublicKey) -> bool {
-        self.0.verify_hashed(msg_hash, pk.as_raw())
+    pub fn verify_hashed(
+        &self,
+        x_real_hashed: &[u8],
+        x_imaginary_hashed: &[u8],
+        pk: &PublicKey,
+    ) -> bool {
+        self.0
+            .verify_hashed(x_real_hashed, x_imaginary_hashed, pk.as_raw())
     }
 
     /// Returns the underlying signature.
@@ -41,7 +51,9 @@ impl Signature {
 
     /// Returns a new empty signature.
     pub fn empty_signature() -> Self {
-        let empty: Vec<u8> = vec![0; 97];
+        let mut empty: Vec<u8> = vec![0; 96];
+        // TODO: Modify the way flags are used (b_flag should not be used for empty_signature in the future)
+        empty[0] += u8::pow(2, 6);
         Signature(RawSignature::from_bytes(&empty).unwrap())
     }
 }
@@ -85,7 +97,7 @@ mod tests {
     pub fn test_ssz_round_trip() {
         let keypair = Keypair::random();
 
-        let original = Signature::new(&[42, 42], &keypair.sk);
+        let original = Signature::new(&[42, 42], 0, &keypair.sk);
 
         let bytes = ssz_encode(&original);
         let (decoded, _) = Signature::ssz_decode(&bytes, 0).unwrap();
@@ -99,9 +111,13 @@ mod tests {
 
         let sig_as_bytes: Vec<u8> = sig.as_raw().as_bytes();
 
-        assert_eq!(sig_as_bytes.len(), 97);
-        for one_byte in sig_as_bytes.iter() {
-            assert_eq!(*one_byte, 0);
+        assert_eq!(sig_as_bytes.len(), 96);
+        for (i, one_byte) in sig_as_bytes.iter().enumerate() {
+            if i == 0 {
+                assert_eq!(*one_byte, u8::pow(2, 6));
+            } else {
+                assert_eq!(*one_byte, 0);
+            }
         }
     }
 }