crypto: Signature of all zero bytes should be Unknown

Currently defaults to Ed25519, which does not match octez reference

CHANGELOG.md

@@ -32,6 +32,7 @@ parameterized by the lifetime of the input byte slice.
 - Add explicit prefix check during base58check decoding.
 - Hash input before signing with `SecretKeyEd25519`, to match octez impl.
 - Fix `BlsSignature` base58 check encoding/decoding.
+- Fix all zeros signature encoding: should be `Unknown` rather than defaulting to `Ed25519`.
 
 ### Security
 

crypto/src/hash.rs

@@ -465,12 +465,8 @@ impl HashType {
             Err(FromBytesError::InvalidSize)
         } else {
             let mut hash = Vec::with_capacity(self.base58check_prefix().len() + data.len());
-            if matches!(self, Self::UnknownSignature) && data == [0; Self::Ed25519Signature.size()]
-            {
-                hash.extend(Self::Ed25519Signature.base58check_prefix());
-            } else {
-                hash.extend(self.base58check_prefix());
-            }
+
+            hash.extend(self.base58check_prefix());
             hash.extend(data);
             hash.to_base58check()
                 // currently the error is returned if the input lenght exceeds 128 bytes

crypto/src/signature.rs

@@ -128,3 +128,14 @@ impl ::std::fmt::Display for Signature {
         write!(f, "{}", self.to_base58_check())
     }
 }
+
+#[cfg(test)]
+mod test {
+    #[test]
+    fn test() {
+        assert_eq!(
+            &super::Signature::try_from([0; 64].to_vec()).unwrap().to_base58_check(),
+            "sigMzJ4GVAvXEd2RjsKGfG2H9QvqTSKCZsuB2KiHbZRGFz72XgF6KaKADznh674fQgBatxw3xdHqTtMHUZAGRprxy64wg1aq"
+        );
+    }
+}