Convert sighashes to messages non-fallibly

cfd_protocol/src/lib.rs

@@ -112,8 +112,7 @@ pub fn build_cfd_transactions(
             taker.lock_amount,
         );
 
-        let sighash =
-            secp256k1_zkp::Message::from_slice(&tx.sighash()).expect("sighash is valid message");
+        let sighash = tx.sighash().to_message();
         let sig = SECP256K1.sign(&sighash, &identity_sk);
 
         (tx.inner, sig)
@@ -200,7 +199,7 @@ pub fn spending_tx_sighash(
         spent_amount.as_sat(),
         SigHashType::All,
     );
-    secp256k1_zkp::Message::from_slice(&sighash).expect("sighash is valid message")
+    sighash.to_message()
 }
 
 pub fn finalize_spend_transaction(
@@ -293,7 +292,7 @@ pub fn punish_transaction(
         tx
     };
 
-    let digest = SigHashCache::new(&punish_tx).signature_hash(
+    let sighash = SigHashCache::new(&punish_tx).signature_hash(
         0,
         &commit_descriptor.script_code(),
         commit_amount,
@@ -309,13 +308,10 @@ pub fn punish_transaction(
             key: pk,
         };
         let pk_hash = pk.pubkey_hash();
-        let sig_sk = SECP256K1.sign(&secp256k1_zkp::Message::from_slice(&digest)?, &sk);
+        let sig_sk = SECP256K1.sign(&sighash.to_message(), &sk);
 
         let publish_them_pk_hash = publish_them_pk.pubkey_hash();
-        let sig_publish_other = SECP256K1.sign(
-            &secp256k1_zkp::Message::from_slice(&digest)?,
-            &publish_them_sk,
-        );
+        let sig_publish_other = SECP256K1.sign(&sighash.to_message(), &publish_them_sk);
 
         let revocation_them_pk = PublicKey::from_private_key(
             SECP256K1,
@@ -326,10 +322,7 @@ pub fn punish_transaction(
             },
         );
         let revocation_them_pk_hash = revocation_them_pk.pubkey_hash();
-        let sig_revocation_other = SECP256K1.sign(
-            &secp256k1_zkp::Message::from_slice(&digest)?,
-            &revocation_them_sk,
-        );
+        let sig_revocation_other = SECP256K1.sign(&sighash.to_message(), &revocation_them_sk);
 
         satisfier.insert(pk_hash.as_hash(), (pk, (sig_sk, SigHashType::All)));
 
@@ -589,7 +582,7 @@ impl ContractExecutionTransaction {
 
         Ok(EcdsaAdaptorSignature::encrypt(
             SECP256K1,
-            &secp256k1_zkp::Message::from_slice(&self.sighash).expect("sighash is valid message"),
+            &self.sighash.to_message(),
             &sk,
             &signature_point,
         ))
@@ -736,7 +729,7 @@ impl CommitTransaction {
     fn encsign(&self, sk: SecretKey, publish_them_pk: &PublicKey) -> EcdsaAdaptorSignature {
         EcdsaAdaptorSignature::encrypt(
             SECP256K1,
-            &secp256k1_zkp::Message::from_slice(&self.sighash).expect("sighash is valid message"),
+            &self.sighash.to_message(),
             &sk,
             &publish_them_pk.key,
         )
@@ -875,6 +868,19 @@ impl TransactionExt for bitcoin::Transaction {
     }
 }
 
+trait SigHashExt {
+    fn to_message(self) -> secp256k1_zkp::Message;
+}
+
+impl SigHashExt for SigHash {
+    fn to_message(self) -> secp256k1_zkp::Message {
+        use secp256k1_zkp::bitcoin_hashes::Hash;
+        let hash = secp256k1_zkp::bitcoin_hashes::sha256d::Hash::from_inner(*self.as_inner());
+
+        hash.into()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;