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test_onion.py: make it possible to build an onion
switched from pyelliptic to hmac/binascii/cryptography for standard functions use our own ECDH implementation to better match the one from secp256k1 finally, add function to create an encrypted onion
This commit is contained in:
Anthony Towns
parent
bb26fc3026
commit
8b0635f7d3
@ -2,13 +2,28 @@
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import sys
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from pyelliptic import ecc
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from pyelliptic import Cipher
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from pyelliptic.hash import hmac_sha256
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from hashlib import sha256
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from binascii import hexlify, unhexlify
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import hmac
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import random
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from cryptography.hazmat.primitives.ciphers import Cipher, modes, algorithms
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from cryptography.hazmat.primitives.ciphers.algorithms import AES
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from cryptography.hazmat.primitives.ciphers.modes import CTR
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from cryptography.hazmat.backends import default_backend
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# http://cryptography.io
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from pyelliptic import ecc
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class MyEx(Exception): pass
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def hmac_sha256(k, m):
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return hmac.new(k, m, sha256).digest()
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hexlify = ecc.hexlify
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unhexlify = ecc.unhexlify
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## pyelliptic doesn't support compressed pubkey representations
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## so we have to add some code...
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@ -22,6 +37,74 @@ OpenSSL.EC_POINT_set_compressed_coordinates_GFp.argtypes = [
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ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_int,
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ctypes.c_void_p]
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def ecc_ecdh_key(sec, pub):
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assert isinstance(sec, ecc.ECC)
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if isinstance(pub, ecc.ECC):
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pub = pub.get_pubkey()
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#return sec.get_ecdh_key(pub)
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pubkey_x, pubkey_y = ecc.ECC._decode_pubkey(pub, 'binary')
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other_key = other_pub_key_x = other_pub_key_y = other_pub_key = None
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own_priv_key = res = res_x = res_y = None
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try:
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other_key = OpenSSL.EC_KEY_new_by_curve_name(sec.curve)
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if other_key == 0:
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raise Exception("[OpenSSL] EC_KEY_new_by_curve_name FAIL ... " + OpenSSL.get_error())
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other_pub_key_x = OpenSSL.BN_bin2bn(pubkey_x, len(pubkey_x), 0)
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other_pub_key_y = OpenSSL.BN_bin2bn(pubkey_y, len(pubkey_y), 0)
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other_group = OpenSSL.EC_KEY_get0_group(other_key)
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other_pub_key = OpenSSL.EC_POINT_new(other_group)
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if (other_pub_key == None):
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raise Exception("[OpenSSl] EC_POINT_new FAIL ... " + OpenSSL.get_error())
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if (OpenSSL.EC_POINT_set_affine_coordinates_GFp(other_group,
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other_pub_key,
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other_pub_key_x,
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other_pub_key_y,
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0)) == 0:
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raise Exception(
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"[OpenSSL] EC_POINT_set_affine_coordinates_GFp FAIL ..." + OpenSSL.get_error())
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own_priv_key = OpenSSL.BN_bin2bn(sec.privkey, len(sec.privkey), 0)
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res = OpenSSL.EC_POINT_new(other_group)
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if (OpenSSL.EC_POINT_mul(other_group, res, 0, other_pub_key, own_priv_key, 0)) == 0:
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raise Exception(
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"[OpenSSL] EC_POINT_mul FAIL ..." + OpenSSL.get_error())
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res_x = OpenSSL.BN_new()
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res_y = OpenSSL.BN_new()
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if (OpenSSL.EC_POINT_get_affine_coordinates_GFp(other_group, res,
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res_x,
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res_y, 0
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)) == 0:
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raise Exception(
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"[OpenSSL] EC_POINT_get_affine_coordinates_GFp FAIL ... " + OpenSSL.get_error())
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resx = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(res_x))
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resy = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(res_y))
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OpenSSL.BN_bn2bin(res_x, resx)
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resx = resx.raw
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OpenSSL.BN_bn2bin(res_y, resy)
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resy = resy.raw
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return resx, resy
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finally:
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if other_key: OpenSSL.EC_KEY_free(other_key)
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if other_pub_key_x: OpenSSL.BN_free(other_pub_key_x)
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if other_pub_key_y: OpenSSL.BN_free(other_pub_key_y)
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if other_pub_key: OpenSSL.EC_POINT_free(other_pub_key)
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if own_priv_key: OpenSSL.BN_free(own_priv_key)
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if res: OpenSSL.EC_POINT_free(res)
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if res_x: OpenSSL.BN_free(res_x)
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if res_y: OpenSSL.BN_free(res_y)
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def get_pos_y_for_x(pubkey_x, yneg=0):
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key = pub_key = pub_key_x = pub_key_y = None
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try:
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@ -62,6 +145,34 @@ class Onion(object):
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MSG_LEN = 128
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ZEROES = b"\x00" * (HMAC_LEN + PKEY_LEN + MSG_LEN)
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@staticmethod
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def tweak_sha(sha, d):
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sha = sha.copy()
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sha.update(d)
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return sha.digest()
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@classmethod
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def get_ecdh_secrets(cls, sec, pkey_x, pkey_y):
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pkey = unhexlify('04') + pkey_x + pkey_y
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tmp_key = ecc.ECC(curve='secp256k1', pubkey=pkey)
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sec_x, sec_y = ecc_ecdh_key(sec, tmp_key)
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b = '\x02' if ord(sec_y[-1]) % 2 == 0 else '\x03'
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sec = sha256(sha256(b + sec_x).digest())
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enckey = cls.tweak_sha(sec, b'\x00')[:16]
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hmac = cls.tweak_sha(sec, b'\x01')
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iv = cls.tweak_sha(sec, b'\x02')[:16]
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pad_iv = cls.tweak_sha(sec, b'\x03')[:16]
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return enckey, hmac, iv, pad_iv
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def enc_pad(self, enckey, pad_iv):
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aes = Cipher(AES(enckey), CTR(pad_iv),
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default_backend()).encryptor()
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return aes.update(self.ZEROES)
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class OnionDecrypt(Onion):
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def __init__(self, onion, my_ecc):
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self.my_ecc = my_ecc
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@ -77,47 +188,104 @@ class Onion(object):
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self.get_secrets()
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def decrypt(self):
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ctx = Cipher(self.enckey, self.pad_iv, 1, ciphername='aes-128-ctr')
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pad = ctx.ciphering(self.ZEROES)
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pad = self.enc_pad(self.enckey, self.pad_iv)
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ctx = Cipher(self.enckey, self.iv, 0, ciphername='aes-128-ctr')
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self.fwd = pad + ctx.ciphering(self.onion[:self.fwd_end])
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self.msg = ctx.ciphering(self.onion[self.fwd_end:self.msg_end])
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def tweak_sha(self, sha, d):
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sha = sha.copy()
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sha.update(d)
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return sha.digest()
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aes = Cipher(AES(self.enckey), CTR(self.iv),
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default_backend()).decryptor()
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self.fwd = pad + aes.update(self.onion[:self.fwd_end])
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self.msg = aes.update(self.onion[self.fwd_end:self.msg_end])
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def get_secrets(self):
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pkey_x = self.pkey
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pkey_y = get_pos_y_for_x(pkey_x)
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pkey = unhexlify('04') + pkey_x + pkey_y
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tmp_key = ecc.ECC(curve='secp256k1', pubkey=pkey)
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sec_x = self.my_ecc.get_ecdh_key(tmp_key.get_pubkey())
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sec_1 = sha256(sha256(b"\x02" + sec_x).digest())
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sec_2 = sha256(sha256(b"\x03" + sec_x).digest())
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sec = None
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if self.check_hmac(self.tweak_sha(sec_1, b'\x01')):
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sec = sec_1
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if self.check_hmac(self.tweak_sha(sec_2, b'\x01')):
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sec = sec_2
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if sec is None:
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pkey_y = get_pos_y_for_x(pkey_x) # always positive by design
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enckey, hmac, iv, pad_iv = self.get_ecdh_secrets(self.my_ecc, pkey_x, pkey_y)
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if not self.check_hmac(hmac):
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raise Exception("HMAC did not verify")
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self.enckey = self.tweak_sha(sec, b'\x00')[:16]
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self.iv = self.tweak_sha(sec, b'\x02')[:16]
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self.pad_iv = self.tweak_sha(sec, b'\x03')[:16]
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self.enckey = enckey
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self.iv = iv
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self.pad_iv = pad_iv
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def check_hmac(self, hmac_key):
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calc = hmac_sha256(hmac_key, self.onion[:-self.HMAC_LEN])
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return calc == self.hmac
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if __name__ == "__main__":
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class OnionEncrypt(Onion):
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def __init__(self, msgs, pubkeys):
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assert len(msgs) == len(pubkeys)
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assert 0 < len(msgs) <= 20
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assert all( len(m) <= self.MSG_LEN for m in msgs )
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msgs = [m + "\0"*(self.MSG_LEN - len(m)) for m in msgs]
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pubkeys = [ecc.ECC(pubkey=pk, curve='secp256k1') for pk in pubkeys]
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n = len(msgs)
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tmpkeys = []
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tmppubkeys = []
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for i in range(n):
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while True:
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t = ecc.ECC(curve='secp256k1')
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if ord(t.pubkey_y[-1]) % 2 == 0:
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break
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# or do the math to "flip" the secret key and pub key
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tmpkeys.append(t)
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tmppubkeys.append(t.pubkey_x)
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enckeys, hmacs, ivs, pad_ivs = zip(*[self.get_ecdh_secrets(tmpkey, pkey.pubkey_x, pkey.pubkey_y)
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for tmpkey, pkey in zip(tmpkeys, pubkeys)])
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# padding takes the form:
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# E_(n-1)(0000s)
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# D_(n-1)(
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# E(n-2)(0000s)
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# D(n-2)(
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# ...
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# )
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# )
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padding = ""
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for i in range(n-1):
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pad = self.enc_pad(enckeys[i], pad_ivs[i])
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aes = Cipher(AES(enckeys[i]), CTR(ivs[i]),
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default_backend()).decryptor()
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padding = pad + aes.update(padding)
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if n < 20:
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padding += str(bytearray(random.getrandbits(8)
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for _ in range(len(self.ZEROES) * (20-n))))
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# to encrypt the message we need to bump the counter past all
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# the padding, then just encrypt the final message
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aes = Cipher(AES(enckeys[-1]), CTR(ivs[-1]),
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default_backend()).encryptor()
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aes.update(padding) # don't care about cyphertext
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msgenc = aes.update(msgs[-1])
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msgenc = padding + msgenc + tmppubkeys[-1]
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del padding
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msgenc += hmac_sha256(hmacs[-1], msgenc)
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# *PHEW*
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# now iterate
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for i in reversed(range(n-1)):
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# drop the padding this node will add
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msgenc = msgenc[len(self.ZEROES):]
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# adding the msg
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msgenc += msgs[i]
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# encrypt it
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aes = Cipher(AES(enckeys[i]), CTR(ivs[i]),
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default_backend()).encryptor()
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msgenc = aes.update(msgenc)
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# add the tmp key
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msgenc += tmppubkeys[i]
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# add the hmac
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msgenc += hmac_sha256(hmacs[i], msgenc)
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self.onion = msgenc
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def decode_from_file(f):
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keys = []
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msg = ""
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for ln in sys.stdin.readlines():
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for ln in f.readlines():
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if ln.startswith(" * Keypair "):
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w = ln.strip().split()
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idx = int(w[2].strip(":"))
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@ -135,9 +303,27 @@ if __name__ == "__main__":
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assert msg != ""
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for k in keys:
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o = Onion(msg, k)
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o = OnionDecrypt(msg, k)
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o.decrypt()
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print o.msg
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msg = o.fwd
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print "done"
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if __name__ == "__main__":
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if len(sys.argv) > 1 and sys.argv[1] == "generate":
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if len(sys.argv) == 3:
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n = int(sys.argv[2])
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else:
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n = 20
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servers = [ecc.ECC(curve='secp256k1') for _ in range(n)]
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server_pubs = [s.get_pubkey() for s in servers]
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msgs = ["Howzit %d..." % (i,) for i in range(n)]
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o = OnionEncrypt(msgs, server_pubs)
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for i, s in enumerate(servers):
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print " * Keypair %d: %s %s" % (
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i, hexlify(s.privkey), hexlify(s.get_pubkey()))
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print " * Message: %s" % (hexlify(o.onion))
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else:
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decode_from_file(sys.stdin)
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