isValidBitcoinDERSignature static method

bool isValidBitcoinDERSignature(List<int> signature)

Implementation

static bool isValidBitcoinDERSignature(List<int> signature) {
  if (signature.length < 9 || signature.length > 73) {
    return false;
  }

  if (signature[0] != 0x30) {
    return false;
  }
  if (signature[1] != signature.length - 3) {
    return false;
  }
  int lenR = signature[3];
  if (5 + lenR >= signature.length) {
    return false;
  }

  int lenS = signature[5 + lenR];
  if ((7 + lenR + lenS) != signature.length) {
    return false;
  }

  // Verify R and S are positive integers (first byte cannot be negative)
  if (signature[4] & 0x80 != 0) {
    return false;
  }
  if (lenR > 1 && (signature[4] == 0x00) && (signature[5] & 0x80 != 0)) {
    return false;
  }
  if (signature[lenR + 4] != 0x02) return false;
  if (lenS == 0) return false;
  // Negative numbers are not allowed for S.
  if ((signature[lenR + 6] & 0x80) != 0) return false;
  // Null bytes at the start of S are not allowed, unless S would otherwise be
  // interpreted as a negative number.
  if (lenS > 1 &&
      (signature[lenR + 6] == 0x00) &&
      (signature[lenR + 7] & 0x80 != 0)) {
    return false;
  }
  return true;
}