Accept ECDSA signatures shorter than 71 bytes

src/error.rs

@@ -56,6 +56,10 @@ pub enum Error {
   SigHashTypeInvalid {
     source: bitcoin::sighash::InvalidSighashTypeError,
   },
+  #[snafu(display("Non-standard sighash type: {source}"))]
+  SigHashTypeNonStandard {
+    source: bitcoin::sighash::NonStandardSighashTypeError,
+  },
   #[snafu(display("Unsupported sighash type `{sighash_type}`"))]
   SigHashTypeUnsupported { sighash_type: String },
   #[snafu(display("Not key path spend"))]
@@ -68,10 +72,6 @@ pub enum Error {
   PublicKeyMismatch,
   #[snafu(display("At least one private key is required"))]
   NoPrivateKeys,
-  #[snafu(display("Non-standard sighash type: {source}"))]
-  SigHashTypeNonStandard {
-    source: bitcoin::sighash::NonStandardSighashTypeError,
-  },
   #[snafu(display("Signer's public key not present in multisig script"))]
   UnknownSigner,
   #[snafu(display("Duplicate private key provided"))]

src/lib.rs

@@ -274,6 +274,22 @@ mod tests {
     );
   }
 
+  #[test]
+  fn verify_p2wpkh_signature_shorter_than_71_bytes() {
+    // ECDSA signatures are not fixed length: this signature's DER encoding is 69
+    // bytes (r serializes to 31 bytes), i.e. 70 bytes with the sighash flag, below
+    // the usual 71/72. It is valid and `sign_simple` produces it, so `verify`
+    // must accept it. Regenerate with:
+    //   sign::sign_simple_encoded(SEGWIT_ADDRESS, "probe-266", WIF_PRIVATE_KEY)
+    assert!(
+      verify::verify_simple_encoded(
+        SEGWIT_ADDRESS,
+        "probe-266",
+        "AkYwQwIgdHvqo7c5BbXCr0O5xWkT1qoihgF5oaKXoFlzuegR+ZICHxoQGPcMKj+iUTymjR5tC+uN7arZcZHUv7BMyf6rwJoBIQLH8SADGWRClD2FiOAa7oQEI8xU/BUhUmo7hcKwy9WIcg=="
+      ).is_ok()
+    );
+  }
+
   #[test]
   fn simple_sign_p2wpkh() {
     assert_eq!(

src/verify.rs

@@ -184,23 +184,23 @@ fn verify_full_p2wpkh(
     return Err(Error::ToSignInvalid);
   }
 
+  if encoded_signature.is_empty() {
+    return Err(Error::SignatureLength {
+      length: 0,
+      encoded_signature,
+    });
+  }
+
   let signature_length = encoded_signature.len();
 
-  let (signature, sighash_type) = match signature_length {
-    71 | 72 => (
-      bitcoin::secp256k1::ecdsa::Signature::from_der(
-        &encoded_signature.as_slice()[..signature_length - 1],
-      )
-      .context(error::SignatureInvalid)?,
-      EcdsaSighashType::from_consensus(encoded_signature[signature_length - 1] as u32),
-    ),
-    _ => {
-      return Err(Error::SignatureLength {
-        length: encoded_signature.len(),
-        encoded_signature,
-      })
-    }
-  };
+  let signature = bitcoin::secp256k1::ecdsa::Signature::from_der(
+    &encoded_signature.as_slice()[..signature_length - 1],
+  )
+  .context(error::SignatureInvalid)?;
+
+  let sighash_type =
+    EcdsaSighashType::from_standard(encoded_signature[signature_length - 1] as u32)
+      .context(error::SigHashTypeNonStandard)?;
 
   if !(sighash_type == EcdsaSighashType::All) {
     return Err(Error::SigHashTypeUnsupported {