Implemented sign_prehashed for ecdsa::Keypair and eth::Keypair (#…

…1598)

* Implemented `sign_prehashed` for `eth::Keypair`

* missing import

* fmt

* Implemented `sign_prehashed` for `ecdsa::Keypair`

* use `[u8; 32]` type

* ditched From impl

signer/src/ecdsa.rs

@@ -160,8 +160,12 @@ impl Keypair {
 
     /// Sign some message. These bytes can be used directly in a Substrate `MultiSignature::Ecdsa(..)`.
     pub fn sign(&self, message: &[u8]) -> Signature {
-        let message_hash = sp_crypto_hashing::blake2_256(message);
-        let wrapped = Message::from_digest_slice(&message_hash).expect("Message is 32 bytes; qed");
+        self.sign_prehashed(&sp_crypto_hashing::blake2_256(message))
+    }
+
+    /// Signs a pre-hashed message.
+    pub fn sign_prehashed(&self, message_hash: &[u8; 32]) -> Signature {
+        let wrapped = Message::from_digest_slice(message_hash).expect("Message is 32 bytes; qed");
         Signature(internal::sign(&self.0.secret_key(), &wrapped))
     }
 }

signer/src/eth.rs

@@ -106,10 +106,12 @@ impl Keypair {
 
     /// Signs an arbitrary message payload.
     pub fn sign(&self, signer_payload: &[u8]) -> Signature {
-        let message_hash = keccak(signer_payload);
-        let wrapped =
-            Message::from_digest_slice(message_hash.as_bytes()).expect("Message is 32 bytes; qed");
-        Signature(ecdsa::internal::sign(&self.0 .0.secret_key(), &wrapped))
+        self.sign_prehashed(&keccak(signer_payload).0)
+    }
+
+    /// Signs a pre-hashed message.
+    pub fn sign_prehashed(&self, message_hash: &[u8; 32]) -> Signature {
+        Signature(self.0.sign_prehashed(message_hash).0)
     }
 }