def compute_their_M_factor(self, usePrimes=False): my_dh_keyid = self.dh_keys.get_my_cur_keyid() their_dh_keyid = self.dh_keys.get_their_cur_keyid() if usePrimes: m1PrimeKey = self.dh_keys.m1prime else: m1PrimeKey = self.dh_keys.m1 # Compute the 32-byte value MA to be the SHA256-HMAC of the following data, using the key m1': mbytes = [] # gy (MPI) mbytes.extend( self.dh_keys.their_public_factor_to_mpi(their_dh_keyid) ) # gx (MPI) mbytes.extend( self.dh_keys.my_public_factor_to_mpi(my_dh_keyid) ) # pubA (PUBKEY) mbytes.extend( OtrDSA.format_key(self.dsa_keys.their_public_key) ) # keyidA (INT) keyid = _OT.zero_pad(_OT.int_to_bytes(their_dh_keyid), 4) mbytes.extend( keyid ) self.their_M = OtrCrypt.get_sha256_hmac(m1PrimeKey, mbytes)
def compute_my_M_and_X_values(self, usePrimes=False):
my_dh_keyid = self.dh_keys.get_my_cur_keyid()
if usePrimes:
cKey = self.dh_keys.cprime
m1Key = self.dh_keys.m1prime
else:
cKey = self.dh_keys.c
m1Key = self.dh_keys.m1
# Compute the 32-byte value MB to be the SHA256-HMAC of the following data, using the key m1:
mbytes = []
# gx (MPI)
mbytes.extend( self.dh_keys.my_public_factor_to_mpi(my_dh_keyid) )
# gy (MPI)
mbytes.extend( self.dh_keys.their_public_factor_to_mpi() )
# pubB (PUBKEY)
mbytes.extend( OtrDSA.format_key(self.dsa_keys.my_public_key) )
# keyidB (INT)
keyid = _OT.zero_pad(_OT.int_to_bytes(my_dh_keyid), 4)
mbytes.extend( keyid )
self.replay.check('M', mbytes)
my_M = OtrCrypt.get_sha256_hmac(m1Key, mbytes)
self.replay.check('hash_M', my_M)
# Let XB be the following structure:
xbytes = []
# pubB (PUBKEY)
xbytes.extend( OtrDSA.format_key(self.dsa_keys.my_public_key) )
# keyidB (INT)
xbytes.extend( keyid )
# sigB(MB) (SIG)
# This is the signature, using the private part of the key pubB, of the 32-byte MB
# (which does not need to be hashed again to produce the signature).
xbytes.extend( self.dsa_keys.sign( my_M ) )
my_X = xbytes
self.replay.check('X', my_X)
# Encrypt XB using AES128-CTR with key c and initial counter value 0.
self.my_enc_sig = OtrCrypt.aes_zero_ctr_crypt(cKey, my_X)
self.replay.check('enc_X', self.my_enc_sig)