Add CryptoStore::ecdsa_sign_prehashed() (paritytech#8838)

* Pair::sign_prehashed()

* add CryptoStore::ecdsa_sign_prehashed()

* add test for testing keystore

* address review comments

client/keystore/src/local.rs

@@ -142,6 +142,15 @@ impl CryptoStore for LocalKeystore {
 	) -> std::result::Result<Option<VRFSignature>, TraitError> {
 		SyncCryptoStore::sr25519_vrf_sign(self, key_type, public, transcript_data)
 	}
+
+	async fn ecdsa_sign_prehashed(
+		&self,
+		id: KeyTypeId,
+		public: &ecdsa::Public,
+		msg: &[u8; 32],
+	) -> std::result::Result<Option<ecdsa::Signature>, TraitError> {
+		SyncCryptoStore::ecdsa_sign_prehashed(self, id, public, msg)
+	}
 }
 
 impl SyncCryptoStore for LocalKeystore {
@@ -301,6 +310,18 @@ impl SyncCryptoStore for LocalKeystore {
 			Ok(None)
 		}
 	}
+
+	fn ecdsa_sign_prehashed(
+		&self,
+		id: KeyTypeId,
+		public: &ecdsa::Public,
+		msg: &[u8; 32],
+	) -> std::result::Result<Option<ecdsa::Signature>, TraitError> {
+		let pair = self.0.read()
+			.key_pair_by_type::<ecdsa::Pair>(public, id)?;
+
+		pair.map(|k| k.sign_prehashed(msg)).map(Ok).transpose()
+	}
 }
 
 impl Into<SyncCryptoStorePtr> for LocalKeystore {

primitives/core/src/ecdsa.rs

@@ -531,6 +531,12 @@ impl Pair {
 			Self::from_seed(&padded_seed)
 		})
 	}
+
+	/// Sign a pre-hashed message
+	pub fn sign_prehashed(&self, message: &[u8; 32]) -> Signature {
+		let message = secp256k1::Message::parse(message);
+		secp256k1::sign(&message, &self.secret).into()
+	}
 }
 
 impl CryptoType for Public {
@@ -552,7 +558,7 @@ impl CryptoType for Pair {
 mod test {
 	use super::*;
 	use hex_literal::hex;
-	use crate::crypto::{DEV_PHRASE, set_default_ss58_version};
+	use crate::{crypto::{DEV_PHRASE, set_default_ss58_version}, keccak_256};
 	use serde_json;
 	use crate::crypto::PublicError;
 
@@ -761,4 +767,28 @@ mod test {
 		// Poorly-sized
 		assert!(deserialize_signature("\"abc123\"").is_err());
 	}
+
+	#[test]
+	fn sign_prehashed_works() {
+		let (pair, _, _) = Pair::generate_with_phrase(Some("password"));
+
+		// `msg` shouldn't be mangled
+		let msg = [0u8; 32];
+		let sig1 = pair.sign_prehashed(&msg);
+		let sig2: Signature = secp256k1::sign(&secp256k1::Message::parse(&msg), &pair.secret).into();
+
+		assert_eq!(sig1, sig2);
+
+		// signature is actually different
+		let sig2 = pair.sign(&msg);
+
+		assert_ne!(sig1, sig2);
+
+		// using pre-hashed `msg` works
+		let msg = keccak_256(b"this should be hashed");
+		let sig1 = pair.sign_prehashed(&msg);
+		let sig2: Signature = secp256k1::sign(&secp256k1::Message::parse(&msg), &pair.secret).into();
+
+		assert_eq!(sig1, sig2);		
+	}
 }

primitives/keystore/src/lib.rs

@@ -194,6 +194,20 @@ pub trait CryptoStore: Send + Sync {
 		public: &sr25519::Public,
 		transcript_data: VRFTranscriptData,
 	) -> Result<Option<VRFSignature>, Error>;
+
+	/// Sign pre-hashed
+	///
+	/// Signs a pre-hashed message with the private key that matches
+	/// the ECDSA public key passed.
+	///
+	/// Returns the SCALE encoded signature if key is found and supported,
+	/// `None` if the key doesn't exist or an error when something failed.
+	async fn ecdsa_sign_prehashed(
+		&self,
+		id: KeyTypeId,
+		public: &ecdsa::Public,
+		msg: &[u8; 32],
+	) -> Result<Option<ecdsa::Signature>, Error>;
 }
 
 /// Sync version of the CryptoStore
@@ -353,6 +367,20 @@ pub trait SyncCryptoStore: CryptoStore + Send + Sync {
 		public: &sr25519::Public,
 		transcript_data: VRFTranscriptData,
 	) -> Result<Option<VRFSignature>, Error>;
+
+	/// Sign pre-hashed
+	///
+	/// Signs a pre-hashed message with the private key that matches
+	/// the ECDSA public key passed.
+	///
+	/// Returns the SCALE encoded signature if key is found and supported,
+	/// `None` if the key doesn't exist or an error when something failed.
+	fn ecdsa_sign_prehashed(
+		&self,
+		id: KeyTypeId,
+		public: &ecdsa::Public,
+		msg: &[u8; 32],
+	) -> Result<Option<ecdsa::Signature>, Error>;
 }
 
 /// A pointer to a keystore.

primitives/keystore/src/testing.rs

@@ -22,6 +22,7 @@ use sp_core::{
 	crypto::{Pair, Public, CryptoTypePublicPair},
 	ed25519, sr25519, ecdsa,
 };
+
 use crate::{
 	{CryptoStore, SyncCryptoStorePtr, Error, SyncCryptoStore},
 	vrf::{VRFTranscriptData, VRFSignature, make_transcript},
@@ -144,6 +145,15 @@ impl CryptoStore for KeyStore {
 	) -> Result<Option<VRFSignature>, Error> {
 		SyncCryptoStore::sr25519_vrf_sign(self, key_type, public, transcript_data)
 	}
+
+	async fn ecdsa_sign_prehashed(
+		&self,
+		id: KeyTypeId,
+		public: &ecdsa::Public,
+		msg: &[u8; 32],
+	) -> Result<Option<ecdsa::Signature>, Error> {
+		SyncCryptoStore::ecdsa_sign_prehashed(self, id, public, msg)
+	}
 }
 
 impl SyncCryptoStore for KeyStore {
@@ -325,6 +335,16 @@ impl SyncCryptoStore for KeyStore {
 			proof,
 		}))
 	}
+
+	fn ecdsa_sign_prehashed(
+		&self,
+		id: KeyTypeId,
+		public: &ecdsa::Public,
+		msg: &[u8; 32],
+	) -> Result<Option<ecdsa::Signature>, Error> {
+		let pair = self.ecdsa_key_pair(id, public);
+		pair.map(|k| k.sign_prehashed(msg)).map(Ok).transpose()
+	}
 }
 
 impl Into<SyncCryptoStorePtr> for KeyStore {
@@ -342,7 +362,7 @@ impl Into<Arc<dyn CryptoStore>> for KeyStore {
 #[cfg(test)]
 mod tests {
 	use super::*;
-	use sp_core::{sr25519, testing::{ED25519, SR25519}};
+	use sp_core::{sr25519, testing::{ED25519, SR25519, ECDSA}};
 	use crate::{SyncCryptoStore, vrf::VRFTranscriptValue};
 
 	#[test]
@@ -416,4 +436,25 @@ mod tests {
 
 		assert!(result.unwrap().is_some());
 	}
+
+	#[test]
+	fn ecdsa_sign_prehashed_works() {
+		let store = KeyStore::new();
+
+		let suri = "//Alice";
+		let pair = ecdsa::Pair::from_string(suri, None).unwrap();
+
+		let msg = sp_core::keccak_256(b"this should be a hashed message");
+
+		// no key in key store
+		let res = SyncCryptoStore::ecdsa_sign_prehashed(&store, ECDSA, &pair.public(), &msg).unwrap();
+		assert!(res.is_none());
+
+		// insert key, sign again
+		let res = SyncCryptoStore::insert_unknown(&store, ECDSA, suri, pair.public().as_ref()).unwrap();
+		assert_eq!((), res);
+
+		let res = SyncCryptoStore::ecdsa_sign_prehashed(&store, ECDSA, &pair.public(), &msg).unwrap();
+		assert!(res.is_some());		
+	}
 }