verifyBtcMessageHeader function

VerifyResult verifyBtcMessageHeader(VerifyBtcMessageHeaderArgs args)

BIP-137: the recovery header names the address type a verifier derives before comparing. A header of the wrong range produces a signature that LOOKS fine (65 bytes, valid base64) but fails every verifier downstream — this check is the only place that difference is visible.

Implementation

VerifyResult verifyBtcMessageHeader(VerifyBtcMessageHeaderArgs args) {
  if (args.signature.isEmpty) {
    return failed('empty signature');
  }
  final header = args.signature[0];
  final range = _headerRangeFor(args.address);
  if (range == null) {
    return unverifiable(
        'address kind has no BIP-137 header range to check against');
  }
  if (header >= range.low && header <= range.high) return verified;
  return failed(
    'recovery header $header does not match a ${range.label} address '
    '(BIP-137 expects ${range.low}..${range.high}); this signature would not '
    'verify against the address it was asked to sign for',
  );
}