message: Make test framework produce lowS signatures
diff: @@ -75,6 +75,9 @@ ssl.EC_POINT_mul.argtypes = [ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p,
  # this specifies the curve used with ECDSA.
  NID_secp256k1 = 714 # from openssl/obj_mac.h
  +SECP256K1_ORDER = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
  +SECP256K1_ORDER_HALF = SECP256K1_ORDER // 2
  +
  # Thx to Sam Devlin for the ctypes magic 64-bit fix.
  def _check_result(val, func, args):
  if val == 0:
  @@ -147,7 +150,7 @@ class CECKey(object):
  r = self.get_raw_ecdh_key(other_pubkey)
  return kdf(r)
  - def sign(self, hash):
  + def sign(self, hash, low_s = True):
  # FIXME: need unit tests for below cases
  if not isinstance(hash, bytes):
  raise TypeError('Hash must be bytes instance; got %r' % hash.__class__)
  @@ -159,7 +162,25 @@ class CECKey(object):
  mb_sig = ctypes.create_string_buffer(sig_size0.value)
  result = ssl.ECDSA_sign(0, hash, len(hash), mb_sig, ctypes.byref(sig_size0), self.k)
  assert 1 == result
  + assert mb_sig.raw[0] == 0x30
  + assert mb_sig.raw[1] == sig_size0.value - 2
  + total_size = mb_sig.raw[1]
  + assert mb_sig.raw[2] == 2
  + r_size = mb_sig.raw[3]
  + assert mb_sig.raw[4 + r_size] == 2
  + s_size = mb_sig.raw[5 + r_size]
  + s_value = int.from_bytes(mb_sig.raw[6+r_size:6+r_size+s_size], byteorder='big')
  + if (not low_s) or s_value <= SECP256K1_ORDER_HALF:
  return mb_sig.raw[:sig_size0.value]
  + else:
  + low_s_value = SECP256K1_ORDER - s_value
  + low_s_bytes = (low_s_value).to_bytes(33, byteorder='big')
  + while len(low_s_bytes) > 1 and low_s_bytes[0] == 0 and low_s_bytes[1] < 0x80:
  + low_s_bytes = low_s_bytes[1:]
  + new_s_size = len(low_s_bytes)
  + new_total_size_byte = (total_size + new_s_size - s_size).to_bytes(1,byteorder='big')
  + new_s_size_byte = (new_s_size).to_bytes(1,byteorder='big')
  + return b'\x30' + new_total_size_byte + mb_sig.raw[2:5+r_size] + new_s_size_byte + low_s_bytes
  def verify(self, hash, sig):
  """Verify a DER signature"""
  