def from_key_verification_start(cls, own_user, own_device, own_fp_key,
other_olm_device, event):
# type: (str, str, str, OlmDevice, KeyVerificationStart) -> Sas
"""Create a SAS object from a KeyVerificationStart event.
Args:
own_user (str): The user id of our own user.
own_device (str): The device id of our own user.
own_fp_key (str): The fingerprint key of our own device that will
be verified by the other client.
other_olm_device (OlmDevice): The Olm device of the other user that
should be verified.
event (KeyVerificationStart): The event that we received from the
other device to start the key verification process.
"""
obj = cls(
own_user,
own_device,
own_fp_key,
other_olm_device,
event.transaction_id,
event.short_authentication_string,
event.message_authentication_codes,
)
obj.we_started_it = False
obj.state = SasState.started
string_content = Api.to_canonical_json(event.source["content"])
obj.commitment = olm.sha256(obj.pubkey + string_content)
obj.key_agreement_protocols = event.key_agreement_protocols
if (Sas._sas_method_v1 != event.method or
(Sas._key_agreement_v1 not in event.key_agreement_protocols
and Sas._key_agreement_v2 not in event.key_agreement_protocols)
or Sas._hash_v1 not in event.hashes
or (Sas._mac_normal not in event.message_authentication_codes
and Sas._mac_old not in event.message_authentication_codes)
or ("emoji" not in event.short_authentication_string
and "decimal" not in event.short_authentication_string)):
obj.state = SasState.canceled
obj.cancel_code, obj.cancel_reason = obj._unknonw_method_error
return obj
def _check_commitment(self, key):
assert self.commitment
calculated_commitment = olm.sha256(
key + Api.to_canonical_json(self.start_verification()))
return self.commitment == calculated_commitment