def createHandshake( self ):
"""
Create and return a ready-to-be-sent UniformDH handshake.
The returned handshake data includes the public key, pseudo-random
padding, the mark and the HMAC. If a UniformDH object has not been
initialised yet, a new instance is created.
"""
assert self.sharedSecret is not None
log.debug("Creating UniformDH handshake message.")
if self.udh is None:
self.udh = obfs3_dh.UniformDH()
publicKey = self.udh.get_public()
assert (const.MAX_PADDING_LENGTH - const.PUBLIC_KEY_LENGTH) >= 0
# Subtract the length of the public key to make the handshake on
# average as long as a redeemed ticket. That should thwart statistical
# length-based attacks.
padding = mycrypto.strongRandom(random.randint(0,
const.MAX_PADDING_LENGTH -
const.PUBLIC_KEY_LENGTH))
# Add a mark which enables efficient location of the HMAC.
mark = mycrypto.HMAC_SHA256_128(self.sharedSecret, publicKey)
# Authenticate the handshake including the current approximate epoch.
mac = mycrypto.HMAC_SHA256_128(self.sharedSecret,
publicKey + padding + mark +
util.getEpoch())
return publicKey + padding + mark + mac
def createHandshake(self):
"""
Create and return a ready-to-be-sent UniformDH handshake.
The returned handshake data includes the public key, pseudo-random
padding, the mark and the HMAC. If a UniformDH object has not been
initialised yet, a new instance is created.
"""
assert self.sharedSecret is not None
log.debug("Creating UniformDH handshake message.")
if self.udh is None:
self.udh = obfs3_dh.UniformDH()
publicKey = self.udh.get_public()
assert (const.MAX_PADDING_LENGTH - const.PUBLIC_KEY_LENGTH) >= 0
# Subtract the length of the public key to make the handshake on
# average as long as a redeemed ticket. That should thwart statistical
# length-based attacks.
padding = mycrypto.strongRandom(
random.randint(0,
const.MAX_PADDING_LENGTH - const.PUBLIC_KEY_LENGTH))
# Add a mark which enables efficient location of the HMAC.
mark = mycrypto.HMAC_SHA256_128(self.sharedSecret, publicKey)
# Authenticate the handshake including the current approximate epoch.
mac = mycrypto.HMAC_SHA256_128(
self.sharedSecret, publicKey + padding + mark + util.getEpoch())
return publicKey + padding + mark + mac
def extractPublicKey( self, data, srvState=None ):
"""
Extract and return a UniformDH public key out of `data'.
Before the public key is touched, the HMAC is verified. If the HMAC is
invalid or some other error occurs, `False' is returned. Otherwise,
the public key is returned. The extracted data is finally drained from
the given `data' object.
"""
assert self.sharedSecret is not None
# Do we already have the minimum amount of data?
if len(data) < (const.PUBLIC_KEY_LENGTH + const.MARK_LENGTH +
const.HMAC_SHA256_128_LENGTH):
return False
log.debug("Attempting to extract the remote machine's UniformDH "
"public key out of %d bytes of data." % len(data))
handshake = data.peek()
# First, find the mark to efficiently locate the HMAC.
publicKey = handshake[:const.PUBLIC_KEY_LENGTH]
mark = mycrypto.HMAC_SHA256_128(self.sharedSecret, publicKey)
index = util.locateMark(mark, handshake)
if not index:
return False
# 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())
if not util.isValidHMAC(myHMAC, existingHMAC, self.sharedSecret):
log.warning("The HMAC is invalid: `%s' vs. `%s'." %
(myHMAC.encode('hex'), existingHMAC.encode('hex')))
return False
# Do nothing if the ticket is replayed. Immediately closing the
# connection would be suspicious.
if srvState is not None and srvState.isReplayed(existingHMAC):
log.warning("The HMAC was already present in the replay table.")
return False
data.drain(index + const.MARK_LENGTH + const.HMAC_SHA256_128_LENGTH)
if srvState is not None:
log.debug("Adding the HMAC authenticating the UniformDH message " \
"to the replay table: %s." % existingHMAC.encode('hex'))
srvState.registerKey(existingHMAC)
return handshake[:const.PUBLIC_KEY_LENGTH]
def extractPublicKey(self, data, srvState=None):
"""
Extract and return a UniformDH public key out of `data'.
Before the public key is touched, the HMAC is verified. If the HMAC is
invalid or some other error occurs, `False' is returned. Otherwise,
the public key is returned. The extracted data is finally drained from
the given `data' object.
"""
assert self.sharedSecret is not None
# Do we already have the minimum amount of data?
if len(data) < (const.PUBLIC_KEY_LENGTH + const.MARK_LENGTH +
const.HMAC_SHA256_128_LENGTH):
return False
log.debug("Attempting to extract the remote machine's UniformDH "
"public key out of %d bytes of data." % len(data))
handshake = data.peek()
# First, find the mark to efficiently locate the HMAC.
publicKey = handshake[:const.PUBLIC_KEY_LENGTH]
mark = mycrypto.HMAC_SHA256_128(self.sharedSecret, publicKey)
index = util.locateMark(mark, handshake)
if not index:
return False
# 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())
if not util.isValidHMAC(myHMAC, existingHMAC, self.sharedSecret):
log.warning("The HMAC is invalid: `%s' vs. `%s'." %
(myHMAC.encode('hex'), existingHMAC.encode('hex')))
return False
# Do nothing if the ticket is replayed. Immediately closing the
# connection would be suspicious.
if srvState is not None and srvState.isReplayed(existingHMAC):
log.warning("The HMAC was already present in the replay table.")
return False
data.drain(index + const.MARK_LENGTH + const.HMAC_SHA256_128_LENGTH)
if srvState is not None:
log.debug("Adding the HMAC authenticating the UniformDH message " \
"to the replay table: %s." % existingHMAC.encode('hex'))
srvState.registerKey(existingHMAC)
return handshake[:const.PUBLIC_KEY_LENGTH]
def createHandshake(self, srvState=None):
"""
Create and return a ready-to-be-sent UniformDH handshake.
The returned handshake data includes the public key, pseudo-random
padding, the mark and the HMAC. If a UniformDH object has not been
initialised yet, a new instance is created.
"""
assert self.sharedSecret is not None
log.debug("Creating UniformDH handshake message.")
if self.udh is None:
self.udh = obfs3_dh.UniformDH()
publicKey = self.udh.get_public()
assert (const.MAX_PADDING_LENGTH - const.PUBLIC_KEY_LENGTH) >= 0
# Subtract the length of the public key to make the handshake on
# average as long as a redeemed ticket. That should thwart statistical
# length-based attacks.
padding = mycrypto.strongRandom(
random.randint(0,
const.MAX_PADDING_LENGTH - const.PUBLIC_KEY_LENGTH))
# 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 + epoch)
if self.weAreServer and (srvState is not None):
log.debug("Adding the HMAC authenticating the server's UniformDH "
"message to the replay table: %s." % mac.encode('hex'))
srvState.registerKey(mac)
return publicKey + padding + mark + mac
def createHandshake( self, srvState=None ):
"""
Create and return a ready-to-be-sent UniformDH handshake.
The returned handshake data includes the public key, pseudo-random
padding, the mark and the HMAC. If a UniformDH object has not been
initialised yet, a new instance is created.
"""
assert self.sharedSecret is not None
log.debug("Creating UniformDH handshake message.")
if self.udh is None:
self.udh = obfs3_dh.UniformDH()
publicKey = self.udh.get_public()
assert (const.MAX_PADDING_LENGTH - const.PUBLIC_KEY_LENGTH) >= 0
# Subtract the length of the public key to make the handshake on
# average as long as a redeemed ticket. That should thwart statistical
# length-based attacks.
padding = mycrypto.strongRandom(random.randint(0,
const.MAX_PADDING_LENGTH -
const.PUBLIC_KEY_LENGTH))
# 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 + epoch)
if self.weAreServer and (srvState is not None):
log.debug("Adding the HMAC authenticating the server's UniformDH "
"message to the replay table: %s." % mac.encode('hex'))
srvState.registerKey(mac)
return publicKey + padding + mark + mac
def createTicketMessage(rawTicket, HMACKey):
"""
Create and return a ready-to-be-sent ticket authentication message.
Pseudo-random padding and a mark are added to `rawTicket' and the result is
then authenticated using `HMACKey' as key for a HMAC. The resulting
authentication message is then returned.
"""
assert len(rawTicket) == const.TICKET_LENGTH
assert len(HMACKey) == const.TICKET_HMAC_KEY_LENGTH
# Subtract the length of the ticket to make the handshake on
# average as long as a UniformDH handshake message.
padding = mycrypto.strongRandom(
random.randint(0, const.MAX_PADDING_LENGTH - const.TICKET_LENGTH))
mark = mycrypto.HMAC_SHA256_128(HMACKey, rawTicket)
hmac = mycrypto.HMAC_SHA256_128(
HMACKey, rawTicket + padding + mark + util.getEpoch())
return rawTicket + padding + mark + hmac
def createTicketMessage( rawTicket, HMACKey ):
"""
Create and return a ready-to-be-sent ticket authentication message.
Pseudo-random padding and a mark are added to `rawTicket' and the result is
then authenticated using `HMACKey' as key for a HMAC. The resulting
authentication message is then returned.
"""
assert len(rawTicket) == const.TICKET_LENGTH
assert len(HMACKey) == const.TICKET_HMAC_KEY_LENGTH
# Subtract the length of the ticket to make the handshake on
# average as long as a UniformDH handshake message.
padding = mycrypto.strongRandom(random.randint(0,
const.MAX_PADDING_LENGTH -
const.TICKET_LENGTH))
mark = mycrypto.HMAC_SHA256_128(HMACKey, rawTicket)
hmac = mycrypto.HMAC_SHA256_128(HMACKey, rawTicket + padding +
mark + util.getEpoch())
return rawTicket + padding + mark + hmac
def receiveTicket( self, data ):
"""
Extract and verify a potential session ticket.
The given `data' is treated as a session ticket. The ticket is being
decrypted and authenticated (yes, in that order). If all these steps
succeed, `True' is returned. Otherwise, `False' is returned.
"""
if len(data) < (const.TICKET_LENGTH + const.MARK_LENGTH +
const.HMAC_SHA256_128_LENGTH):
return False
potentialTicket = data.peek()
# Now try to decrypt and parse the ticket. We need the master key
# inside to verify the HMAC in the next step.
if not self.decryptedTicket:
newTicket = ticket.decrypt(potentialTicket[:const.TICKET_LENGTH],
self.srvState)
if newTicket != None and newTicket.isValid():
self.deriveSecrets(newTicket.masterKey)
self.decryptedTicket = True
else:
return False
# First, find the mark to efficiently locate the HMAC.
mark = mycrypto.HMAC_SHA256_128(self.recvHMAC,
potentialTicket[:const.TICKET_LENGTH])
index = util.locateMark(mark, potentialTicket)
if not index:
return False
# Now, verify if the HMAC is valid.
existingHMAC = potentialTicket[index + const.MARK_LENGTH:
index + const.MARK_LENGTH +
const.HMAC_SHA256_128_LENGTH]
myHMAC = mycrypto.HMAC_SHA256_128(self.recvHMAC,
potentialTicket[0:
index + const.MARK_LENGTH] +
util.getEpoch())
if not util.isValidHMAC(myHMAC, existingHMAC, self.recvHMAC):
log.warning("The HMAC is invalid: `%s' vs. `%s'." %
(myHMAC.encode('hex'), existingHMAC.encode('hex')))
return False
# Do nothing if the ticket is replayed. Immediately closing the
# connection would be suspicious.
if self.srvState.isReplayed(existingHMAC):
log.warning("The HMAC was already present in the replay table.")
return False
data.drain(index + const.MARK_LENGTH + const.HMAC_SHA256_128_LENGTH)
log.debug("Adding the HMAC authenticating the ticket message to the " \
"replay table: %s." % existingHMAC.encode('hex'))
self.srvState.registerKey(existingHMAC)
log.debug("Switching to state ST_CONNECTED.")
self.protoState = const.ST_CONNECTED
return True
def test5_getEpoch( self ):
e = util.getEpoch()
self.failUnless(isinstance(e, basestring))
