commit 37fb7903588171ce7b73b7eb973590aff2a76736 Author: Philipp Winter <phw@torproject.org> Date: Tue Mar 4 20:34:16 2014 +0100 Make the server simply echo the client's epoch. That's only relevant for UniformDH. --- obfsproxy/transports/scramblesuit/uniformdh.py | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/obfsproxy/transports/scramblesuit/uniformdh.py b/obfsproxy/transports/scramblesuit/uniformdh.py index b070b10..1b59575 100644 --- a/obfsproxy/transports/scramblesuit/uniformdh.py +++ b/obfsproxy/transports/scramblesuit/uniformdh.py @@ -46,6 +46,9 @@ class UniformDH( object ): # Uniform Diffie-Hellman object (implemented in obfs3_dh.py). self.udh = None + # Used by the server so it can simply echo the client's epoch. + self.echoEpoch = None + def getRemotePublicKey( self ): """ Return the cached remote UniformDH public key. @@ -117,13 +120,15 @@ class UniformDH( object ): if not index: return False + self.echoEpoch = util.getEpoch() + # Now that we know where the authenticating HMAC is: verify it. hmacStart = index + const.MARK_LENGTH existingHMAC = handshake[hmacStart: (hmacStart + const.HMAC_SHA256_128_LENGTH)] myHMAC = mycrypto.HMAC_SHA256_128(self.sharedSecret, handshake[0 : hmacStart] + - util.getEpoch()) + self.echoEpoch) if not util.isValidHMAC(myHMAC, existingHMAC, self.sharedSecret): log.warning("The HMAC is invalid: `%s' vs. `%s'." % @@ -174,10 +179,15 @@ class UniformDH( object ): # Add a mark which enables efficient location of the HMAC. mark = mycrypto.HMAC_SHA256_128(self.sharedSecret, publicKey) + if self.echoEpoch is None: + epoch = util.getEpoch() + else: + epoch = self.echoEpoch + log.debug("Echoing epoch rather than recreating it.") + # Authenticate the handshake including the current approximate epoch. mac = mycrypto.HMAC_SHA256_128(self.sharedSecret, - publicKey + padding + mark + - util.getEpoch()) + publicKey + padding + mark + epoch) return publicKey + padding + mark + mac