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
9 years ago · 8b0635f7d3
1 changed files with 222 additions and 36 deletions
--- a/test/test_onion.py
+++ b/test/test_onion.py
@ -2,13 +2,28 @@

 import sys

-from pyelliptic import ecc
-from pyelliptic import Cipher
-from pyelliptic.hash import hmac_sha256
 from hashlib import sha256
+from binascii import hexlify, unhexlify
+import hmac
+import random
+
+from cryptography.hazmat.primitives.ciphers import Cipher, modes, algorithms
+from cryptography.hazmat.primitives.ciphers.algorithms import AES
+from cryptography.hazmat.primitives.ciphers.modes import CTR
+from cryptography.hazmat.backends import default_backend
+# http://cryptography.io
+
+from pyelliptic import ecc
+
+class MyEx(Exception): pass
+
+def hmac_sha256(k, m):
+    return hmac.new(k, m, sha256).digest()
+
+
+
+

-hexlify = ecc.hexlify
-unhexlify = ecc.unhexlify

 ## pyelliptic doesn't support compressed pubkey representations
 ## so we have to add some code...
@ -22,6 +37,74 @@ OpenSSL.EC_POINT_set_compressed_coordinates_GFp.argtypes = [
    ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_int,
    ctypes.c_void_p]

+def ecc_ecdh_key(sec, pub):
+    assert isinstance(sec, ecc.ECC)
+    if isinstance(pub, ecc.ECC):
+        pub = pub.get_pubkey()
+    #return sec.get_ecdh_key(pub)
+
+    pubkey_x, pubkey_y = ecc.ECC._decode_pubkey(pub, 'binary')
+
+    other_key = other_pub_key_x = other_pub_key_y = other_pub_key = None
+    own_priv_key = res = res_x = res_y = None
+    try:
+            other_key = OpenSSL.EC_KEY_new_by_curve_name(sec.curve)
+            if other_key == 0:
+                raise Exception("[OpenSSL] EC_KEY_new_by_curve_name FAIL ... " + OpenSSL.get_error())
+
+            other_pub_key_x = OpenSSL.BN_bin2bn(pubkey_x, len(pubkey_x), 0)
+            other_pub_key_y = OpenSSL.BN_bin2bn(pubkey_y, len(pubkey_y), 0)
+
+            other_group = OpenSSL.EC_KEY_get0_group(other_key)
+            other_pub_key = OpenSSL.EC_POINT_new(other_group)
+            if (other_pub_key == None):
+                raise Exception("[OpenSSl] EC_POINT_new FAIL ... " + OpenSSL.get_error())
+
+            if (OpenSSL.EC_POINT_set_affine_coordinates_GFp(other_group,
+                                                            other_pub_key,
+                                                            other_pub_key_x,
+                                                            other_pub_key_y,
+                                                            0)) == 0:
+                raise Exception(
+                    "[OpenSSL] EC_POINT_set_affine_coordinates_GFp FAIL ..." + OpenSSL.get_error())
+
+            own_priv_key = OpenSSL.BN_bin2bn(sec.privkey, len(sec.privkey), 0)
+
+            res = OpenSSL.EC_POINT_new(other_group)
+            if (OpenSSL.EC_POINT_mul(other_group, res, 0, other_pub_key, own_priv_key, 0)) == 0:
+                raise Exception(
+                    "[OpenSSL] EC_POINT_mul FAIL ..." + OpenSSL.get_error())
+
+            res_x = OpenSSL.BN_new()
+            res_y = OpenSSL.BN_new()
+
+            if (OpenSSL.EC_POINT_get_affine_coordinates_GFp(other_group, res,
+                                                            res_x,
+                                                            res_y, 0
+                                                            )) == 0:
+                raise Exception(
+                    "[OpenSSL] EC_POINT_get_affine_coordinates_GFp FAIL ... " + OpenSSL.get_error())
+
+            resx = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(res_x))
+            resy = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(res_y))
+
+            OpenSSL.BN_bn2bin(res_x, resx)
+            resx = resx.raw
+            OpenSSL.BN_bn2bin(res_y, resy)
+            resy = resy.raw
+
+            return resx, resy
+
+    finally:
+            if other_key: OpenSSL.EC_KEY_free(other_key)
+            if other_pub_key_x: OpenSSL.BN_free(other_pub_key_x)
+            if other_pub_key_y: OpenSSL.BN_free(other_pub_key_y)
+            if other_pub_key: OpenSSL.EC_POINT_free(other_pub_key)
+            if own_priv_key: OpenSSL.BN_free(own_priv_key)
+            if res: OpenSSL.EC_POINT_free(res)
+            if res_x: OpenSSL.BN_free(res_x)
+            if res_y: OpenSSL.BN_free(res_y)
+
 def get_pos_y_for_x(pubkey_x, yneg=0):
    key = pub_key = pub_key_x = pub_key_y = None
    try:
@ -62,6 +145,34 @@ class Onion(object):
    MSG_LEN = 128
    ZEROES = b"\x00" * (HMAC_LEN + PKEY_LEN + MSG_LEN)

+    @staticmethod
+    def tweak_sha(sha, d):
+        sha = sha.copy()
+        sha.update(d)
+        return sha.digest()
+
+    @classmethod
+    def get_ecdh_secrets(cls, sec, pkey_x, pkey_y):
+        pkey = unhexlify('04') + pkey_x + pkey_y
+        tmp_key = ecc.ECC(curve='secp256k1', pubkey=pkey)
+        sec_x, sec_y = ecc_ecdh_key(sec, tmp_key)
+
+        b = '\x02' if ord(sec_y[-1]) % 2 == 0 else '\x03'
+        sec = sha256(sha256(b + sec_x).digest())
+
+        enckey = cls.tweak_sha(sec, b'\x00')[:16]
+        hmac   = cls.tweak_sha(sec, b'\x01')
+        iv     = cls.tweak_sha(sec, b'\x02')[:16]
+        pad_iv = cls.tweak_sha(sec, b'\x03')[:16]
+
+        return enckey, hmac, iv, pad_iv
+
+    def enc_pad(self, enckey, pad_iv):
+        aes = Cipher(AES(enckey), CTR(pad_iv),
+                     default_backend()).encryptor()
+        return aes.update(self.ZEROES)
+
+class OnionDecrypt(Onion):
    def __init__(self, onion, my_ecc):
        self.my_ecc = my_ecc

@ -77,47 +188,104 @@ class Onion(object):
        self.get_secrets()

    def decrypt(self):
-        ctx = Cipher(self.enckey, self.pad_iv, 1, ciphername='aes-128-ctr')
-        pad = ctx.ciphering(self.ZEROES)
+        pad = self.enc_pad(self.enckey, self.pad_iv)

-        ctx = Cipher(self.enckey, self.iv, 0, ciphername='aes-128-ctr')
-        self.fwd = pad + ctx.ciphering(self.onion[:self.fwd_end])
-        self.msg = ctx.ciphering(self.onion[self.fwd_end:self.msg_end])
-
-    def tweak_sha(self, sha, d):
-        sha = sha.copy()
-        sha.update(d)
-        return sha.digest()
+        aes = Cipher(AES(self.enckey), CTR(self.iv),
+                     default_backend()).decryptor()
+        self.fwd = pad + aes.update(self.onion[:self.fwd_end])
+        self.msg = aes.update(self.onion[self.fwd_end:self.msg_end])

    def get_secrets(self):
        pkey_x = self.pkey
-        pkey_y = get_pos_y_for_x(pkey_x)
-        pkey = unhexlify('04') + pkey_x + pkey_y
-        tmp_key = ecc.ECC(curve='secp256k1', pubkey=pkey)
-        sec_x = self.my_ecc.get_ecdh_key(tmp_key.get_pubkey())
-        sec_1 = sha256(sha256(b"\x02" + sec_x).digest())
-        sec_2 = sha256(sha256(b"\x03" + sec_x).digest())
-
-        sec = None
-        if self.check_hmac(self.tweak_sha(sec_1, b'\x01')):
-            sec = sec_1
-        if self.check_hmac(self.tweak_sha(sec_2, b'\x01')):
-            sec = sec_2
-        if sec is None:
+        pkey_y = get_pos_y_for_x(pkey_x) # always positive by design
+        enckey, hmac, iv, pad_iv = self.get_ecdh_secrets(self.my_ecc, pkey_x, pkey_y)
+        if not self.check_hmac(hmac):
            raise Exception("HMAC did not verify")
-
-        self.enckey = self.tweak_sha(sec, b'\x00')[:16]
-        self.iv     = self.tweak_sha(sec, b'\x02')[:16]
-        self.pad_iv = self.tweak_sha(sec, b'\x03')[:16]
+        self.enckey = enckey
+        self.iv     = iv
+        self.pad_iv = pad_iv

    def check_hmac(self, hmac_key):
        calc = hmac_sha256(hmac_key, self.onion[:-self.HMAC_LEN])
        return calc == self.hmac

-if __name__ == "__main__":
+class OnionEncrypt(Onion):
+    def __init__(self, msgs, pubkeys):
+        assert len(msgs) == len(pubkeys)
+        assert 0 < len(msgs) <= 20
+        assert all( len(m) <= self.MSG_LEN for m in msgs )
+
+        msgs = [m + "\0"*(self.MSG_LEN - len(m)) for m in msgs]
+        pubkeys = [ecc.ECC(pubkey=pk, curve='secp256k1') for pk in pubkeys]
+        n = len(msgs)
+
+        tmpkeys = []
+        tmppubkeys = []
+        for i in range(n):
+            while True:
+                t = ecc.ECC(curve='secp256k1')
+                if ord(t.pubkey_y[-1]) % 2 == 0:
+                    break
+                # or do the math to "flip" the secret key and pub key
+            tmpkeys.append(t)
+            tmppubkeys.append(t.pubkey_x)
+
+        enckeys, hmacs, ivs, pad_ivs = zip(*[self.get_ecdh_secrets(tmpkey, pkey.pubkey_x, pkey.pubkey_y)
+            for tmpkey, pkey in zip(tmpkeys, pubkeys)])
+
+        # padding takes the form:
+        #  E_(n-1)(0000s)
+        #  D_(n-1)(
+        #      E(n-2)(0000s)
+        #      D(n-2)(
+        #          ...
+        #      )
+        #  )
+
+        padding = ""
+        for i in range(n-1):
+             pad = self.enc_pad(enckeys[i], pad_ivs[i])
+             aes = Cipher(AES(enckeys[i]), CTR(ivs[i]),
+                     default_backend()).decryptor()
+             padding = pad + aes.update(padding)
+
+        if n < 20:
+            padding += str(bytearray(random.getrandbits(8)
+                             for _ in range(len(self.ZEROES) * (20-n))))
+
+        # to encrypt the message we need to bump the counter past all
+        # the padding, then just encrypt the final message
+        aes = Cipher(AES(enckeys[-1]), CTR(ivs[-1]),
+            default_backend()).encryptor()
+        aes.update(padding) # don't care about cyphertext
+        msgenc = aes.update(msgs[-1])
+
+        msgenc = padding + msgenc + tmppubkeys[-1]
+        del padding
+        msgenc += hmac_sha256(hmacs[-1], msgenc)
+
+        # *PHEW*
+        # now iterate
+
+        for i in reversed(range(n-1)):
+            # drop the padding this node will add
+            msgenc = msgenc[len(self.ZEROES):]
+            # adding the msg
+            msgenc += msgs[i]
+            # encrypt it
+            aes = Cipher(AES(enckeys[i]), CTR(ivs[i]),
+                default_backend()).encryptor()
+            msgenc = aes.update(msgenc)
+            # add the tmp key
+            msgenc += tmppubkeys[i]
+            # add the hmac
+            msgenc += hmac_sha256(hmacs[i], msgenc)
+        self.onion = msgenc
+
+def decode_from_file(f):
    keys = []
    msg = ""
-    for ln in sys.stdin.readlines():
+    for ln in f.readlines():
        if ln.startswith(" * Keypair "):
            w = ln.strip().split()
            idx = int(w[2].strip(":"))
@ -135,9 +303,27 @@ if __name__ == "__main__":

    assert msg != ""
    for k in keys:
-        o = Onion(msg, k)
+        o = OnionDecrypt(msg, k)
        o.decrypt()
        print o.msg
        msg = o.fwd
-
    print "done"
+
+if __name__ == "__main__":
+    if len(sys.argv) > 1 and sys.argv[1] == "generate":
+        if len(sys.argv) == 3:
+            n = int(sys.argv[2])
+        else:
+            n = 20
+        servers = [ecc.ECC(curve='secp256k1') for _ in range(n)]
+        server_pubs = [s.get_pubkey() for s in servers]
+        msgs = ["Howzit %d..." % (i,) for i in range(n)]
+
+        o = OnionEncrypt(msgs, server_pubs)
+
+        for i, s in enumerate(servers):
+            print " * Keypair %d: %s %s" % (
+                    i, hexlify(s.privkey), hexlify(s.get_pubkey()))
+        print " * Message: %s" % (hexlify(o.onion))
+    else:
+        decode_from_file(sys.stdin)