Move proof_of_possession into bls crate

beacon_chain/utils/bls/src/lib.rs

@@ -1,4 +1,5 @@
 extern crate bls_aggregates;
+extern crate hashing;
 
 pub use self::bls_aggregates::AggregateSignature;
 pub use self::bls_aggregates::AggregatePublicKey;
@@ -8,3 +9,21 @@ pub use self::bls_aggregates::PublicKey;
 pub use self::bls_aggregates::SecretKey;
 
 pub const BLS_AGG_SIG_BYTE_SIZE: usize = 97;
+
+use hashing::proof_of_possession_hash;
+
+/// 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 hash = proof_of_possession_hash(&pubkey.as_bytes());
+    sig.verify_hashed(&hash, &pubkey)
+}
+
+pub fn create_proof_of_possession(keypair: &Keypair)
+    -> Signature
+{
+    let hash = proof_of_possession_hash(&keypair.pk.as_bytes());
+    Signature::new_hashed(&hash, &keypair.sk)
+}