def decodePublicKey(key):
if len(key) != 33:
raise WireFormatException(
"The key field must contain 33 bytes of data.")
try:
key_type = ord(key[0])
except TypeError:
key_type = key[0]
if key_type != KEY_TYPE_25519:
raise WireFormatException("Unknown key type.")
return key[1:]
def messageFromWire(obj):
# Due to the nature the mac is calculated by signal, the authentication
# verification has to be done later in an additional step.
# Remove the mac
mac = obj[-MAC_SIZE:]
obj = obj[:-MAC_SIZE]
# Check and remove the version
obj = checkVersion(obj)
# Unpack the protobuf structure
obj = wtp.SignalMessage.FromString(obj)
if not (obj.HasField("dh_ratchet_key") and obj.HasField("n")
and obj.HasField("ciphertext")):
raise WireFormatException("Message incomplete.")
return {
"ciphertext":
obj.ciphertext,
"header":
doubleratchet.Header(decodePublicKey(obj.dh_ratchet_key), obj.n,
obj.pn),
"additional":
mac
}
def checkVersion(data):
try:
version = ord(data[0])
except TypeError:
version = data[0]
major_version = (version >> 4) & 0x0F
minor_version = (version >> 0) & 0x0F
if major_version < CURRENT_MAJOR_VERSION or minor_version < CURRENT_MINOR_VERSION:
raise WireFormatException("Legacy version detected.")
if major_version > CURRENT_MAJOR_VERSION or minor_version > CURRENT_MINOR_VERSION:
raise WireFormatException("Newer/unknown version detected.")
return data[1:]
def finalizeMessageFromWire(obj, additional):
dr_additional = additional["DoubleRatchet"]
IK_own = dr_additional["ad"][:33]
IK_other = dr_additional["ad"][33:]
key = dr_additional["key"]
mac = calculateMAC(obj[:-MAC_SIZE], key, IK_other, IK_own)
if not additional["WireFormat"] == mac:
raise WireFormatException("Message authentication failed.")
def preKeyMessageFromWire(obj):
obj = checkVersion(obj)
obj = wtp.PreKeySignalMessage.FromString(obj)
if not (obj.HasField("spk_id") and obj.HasField("ek")
and obj.HasField("ik") and obj.HasField("signal_message")
and obj.HasField("otpk_id")):
raise WireFormatException("Pre key message incomplete.")
return {
"session_init_data": {
"registration_id": obj.registration_id,
"otpk_id": obj.otpk_id,
"spk_id": obj.spk_id,
"ek": decodePublicKey(obj.ek),
"ik": decodePublicKey(obj.ik)
},
"message": obj.signal_message,
"additional": None
}