def clear_screens(user_input: 'UserInput', window: 'TxWindow',
settings: 'Settings', queues: 'QueueDict') -> None:
"""Clear/reset screen of Source, Destination, and Networked Computer.
Only send an unencrypted command to Networked Computer if traffic
masking is disabled.
With clear command, sending only the command header is enough.
However, as reset command removes the ephemeral message log on
Receiver Program, Transmitter Program must define the window to
reset (in case, e.g., previous window selection command packet
dropped, and active window state is inconsistent between the
TCB programs).
"""
clear = user_input.plaintext.split()[0] == CLEAR
command = CLEAR_SCREEN if clear else RESET_SCREEN + window.uid
queue_command(command, settings, queues)
clear_screen()
if not settings.traffic_masking:
pt_cmd = UNENCRYPTED_SCREEN_CLEAR if clear else UNENCRYPTED_SCREEN_RESET
packet = UNENCRYPTED_DATAGRAM_HEADER + pt_cmd
queue_to_nc(packet, queues[RELAY_PACKET_QUEUE])
if not clear:
readline.clear_history()
reset_terminal()
def exit_tfc(settings: 'Settings', queues: 'QueueDict',
gateway: 'Gateway') -> None:
"""Exit TFC on all three computers.
To exit TFC as fast as possible, this function starts by clearing
all command queues before sending the exit command to Receiver
Program. It then sends an unencrypted exit command to Relay Program
on Networked Computer. As the `sender_loop` process loads the
unencrypted exit command from queue, it detects the user's
intention, and after outputting the packet, sends the EXIT signal to
Transmitter Program's main() method that's running the
`monitor_processes` loop. Upon receiving the EXIT signal,
`monitor_processes` kills all Transmitter Program's processes and
exits the program.
During local testing, this function adds some delays to prevent TFC
programs from dying when sockets disconnect.
"""
for q in [COMMAND_PACKET_QUEUE, RELAY_PACKET_QUEUE]:
while queues[q].qsize() > 0:
queues[q].get()
queue_command(EXIT_PROGRAM, settings, queues)
if not settings.traffic_masking:
if settings.local_testing_mode:
time.sleep(LOCAL_TESTING_PACKET_DELAY)
time.sleep(gateway.settings.data_diode_sockets * 1.5)
else:
time.sleep(gateway.settings.race_condition_delay)
relay_command = UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_EXIT_COMMAND
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
def get_onion_address_from_user(onion_address_user: str,
queues: 'QueueDict') -> str:
"""Get contact's Onion Address from user."""
while True:
onion_address_contact = box_input("Contact account",
expected_len=ONION_ADDRESS_LENGTH)
error_msg = validate_onion_addr(onion_address_contact,
onion_address_user)
if error_msg:
m_print(error_msg, head=1)
print_on_previous_line(reps=5, delay=1)
if error_msg not in [
"Error: Invalid account length.",
"Error: Account must be in lower case.",
"Error: Can not add reserved account.",
"Error: Can not add own account."
]:
relay_command = UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_ACCOUNT_CHECK + onion_address_contact.encode(
)
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
continue
return onion_address_contact
def deliver_local_key(local_key_packet: bytes, kek: bytes, c_code: bytes,
settings: 'Settings', queues: 'QueueDict') -> None:
"""Deliver encrypted local key to Destination Computer."""
nc_bypass_msg(NC_BYPASS_START, settings)
queue_to_nc(local_key_packet, queues[RELAY_PACKET_QUEUE])
while True:
print_key("Local key decryption key (to Receiver)", kek, settings)
purp_code = ask_confirmation_code("Receiver")
if purp_code == c_code.hex():
nc_bypass_msg(NC_BYPASS_STOP, settings)
break
elif purp_code == "":
phase("Resending local key", head=2)
queue_to_nc(local_key_packet, queues[RELAY_PACKET_QUEUE])
phase(DONE)
print_on_previous_line(
reps=(9 if settings.local_testing_mode else 10))
else:
m_print([
"Incorrect confirmation code. If Receiver did not receive",
"the encrypted local key, resend it by pressing <Enter>."
],
head=1)
print_on_previous_line(
reps=(9 if settings.local_testing_mode else 10), delay=2)
def group_add_member(group_name: str,
purp_members: List['bytes'],
contact_list: 'ContactList',
group_list: 'GroupList',
settings: 'Settings',
queues: 'QueueDict',
master_key: 'MasterKey',
_: Optional[bytes] = None) -> None:
"""Add new member(s) to a specified group."""
if group_name not in group_list.get_list_of_group_names():
if not yes(f"Group {group_name} was not found. Create new group?",
abort=False,
head=1):
raise SoftError("Group creation aborted.",
head=0,
delay=1,
tail_clear=True)
group_create(group_name, purp_members, contact_list, group_list,
settings, queues, master_key)
return None
purp_pub_keys = set(purp_members)
pub_keys = set(contact_list.get_list_of_pub_keys())
before_adding = set(
group_list.get_group(group_name).get_list_of_member_pub_keys())
ok_pub_keys_set = set(pub_keys & purp_pub_keys)
new_in_group_set = set(ok_pub_keys_set - before_adding)
end_assembly = list(before_adding | new_in_group_set)
rejected = list(purp_pub_keys - pub_keys)
already_in_g = list(before_adding & purp_pub_keys)
new_in_group = list(new_in_group_set)
ok_pub_keys = list(ok_pub_keys_set)
if len(end_assembly) > settings.max_number_of_group_members:
raise SoftError(
f"Error: TFC settings only allow {settings.max_number_of_group_members} members per group.",
head_clear=True)
group = group_list.get_group(group_name)
group.add_members(
[contact_list.get_contact_by_pub_key(k) for k in new_in_group])
command = GROUP_ADD + group.group_id + b''.join(ok_pub_keys)
queue_command(command, settings, queues)
group_management_print(ADDED_MEMBERS, new_in_group, contact_list,
group_name)
group_management_print(ALREADY_MEMBER, already_in_g, contact_list,
group_name)
group_management_print(UNKNOWN_ACCOUNTS, rejected, contact_list,
group_name)
if new_in_group:
if yes("Publish the list of new members to involved?", abort=False):
add_packet = (GROUP_MSG_MEMBER_ADD_HEADER + group.group_id +
int_to_bytes(len(before_adding)) +
b''.join(before_adding) + b''.join(new_in_group))
queue_to_nc(add_packet, queues[RELAY_PACKET_QUEUE])
def group_create(group_name: str,
purp_members: List[bytes],
contact_list: 'ContactList',
group_list: 'GroupList',
settings: 'Settings',
queues: 'QueueDict',
_: 'MasterKey',
group_id: Optional[bytes] = None
) -> None:
"""Create a new group.
Validate the group name and determine what members can be added.
"""
error_msg = validate_group_name(group_name, contact_list, group_list)
if error_msg:
raise FunctionReturn(error_msg, head_clear=True)
public_keys = set(contact_list.get_list_of_pub_keys())
purp_pub_keys = set(purp_members)
accepted = list(purp_pub_keys & public_keys)
rejected = list(purp_pub_keys - public_keys)
if len(accepted) > settings.max_number_of_group_members:
raise FunctionReturn(f"Error: TFC settings only allow {settings.max_number_of_group_members} "
f"members per group.", head_clear=True)
if len(group_list) == settings.max_number_of_groups:
raise FunctionReturn(f"Error: TFC settings only allow {settings.max_number_of_groups} groups.", head_clear=True)
header = GROUP_MSG_INVITE_HEADER if group_id is None else GROUP_MSG_JOIN_HEADER
if group_id is None:
while True:
group_id = os.urandom(GROUP_ID_LENGTH)
if group_id not in group_list.get_list_of_group_ids():
break
group_list.add_group(group_name,
group_id,
settings.log_messages_by_default,
settings.show_notifications_by_default,
members=[contact_list.get_contact_by_pub_key(k) for k in accepted])
command = GROUP_CREATE + group_id + group_name.encode() + US_BYTE + b''.join(accepted)
queue_command(command, settings, queues)
group_management_print(NEW_GROUP, accepted, contact_list, group_name)
group_management_print(UNKNOWN_ACCOUNTS, rejected, contact_list, group_name)
if accepted:
if yes("Publish the list of group members to participants?", abort=False):
create_packet = header + group_id + b''.join(accepted)
queue_to_nc(create_packet, queues[RELAY_PACKET_QUEUE])
else:
m_print(f"Created an empty group '{group_name}'.", bold=True, head=1)
def queue_delayer():
"""Place packets to queue after delay."""
time.sleep(0.01)
queues[WINDOW_SELECT_QUEUE].put(window.window_contacts)
time.sleep(0.01)
queue_command(b'test', settings, queues) # 1
queue_message(user_input, window, settings, queues) # 2
queue_message(user_input, window, settings, queues) # 3
queue_command(b'test', settings, queues) # 4
queues[TM_NOISE_COMMAND_QUEUE].put((C_N_HEADER + bytes(PADDING_LENGTH))) # 5
queue_to_nc(UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_EXIT_COMMAND, queues[RELAY_PACKET_QUEUE]) # 6
queue_to_nc(UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_WIPE_COMMAND, queues[RELAY_PACKET_QUEUE]) # 7
queues[SENDER_MODE_QUEUE].put(settings)
def group_rm_member(group_name: str,
purp_members: List[bytes],
contact_list: 'ContactList',
group_list: 'GroupList',
settings: 'Settings',
queues: 'QueueDict',
master_key: 'MasterKey',
_: Optional[bytes] = None) -> None:
"""Remove member(s) from the specified group or remove the group itself."""
if not purp_members:
group_rm_group(group_name, contact_list, group_list, settings, queues,
master_key)
if group_name not in group_list.get_list_of_group_names():
raise FunctionReturn(f"Group '{group_name}' does not exist.",
head_clear=True)
purp_pub_keys = set(purp_members)
pub_keys = set(contact_list.get_list_of_pub_keys())
before_removal = set(
group_list.get_group(group_name).get_list_of_member_pub_keys())
ok_pub_keys_set = set(purp_pub_keys & pub_keys)
removable_set = set(before_removal & ok_pub_keys_set)
remaining = list(before_removal - removable_set)
not_in_group = list(ok_pub_keys_set - before_removal)
rejected = list(purp_pub_keys - pub_keys)
removable = list(removable_set)
ok_pub_keys = list(ok_pub_keys_set)
group = group_list.get_group(group_name)
group.remove_members(removable)
command = GROUP_REMOVE + group.group_id + b''.join(ok_pub_keys)
queue_command(command, settings, queues)
group_management_print(REMOVED_MEMBERS, removable, contact_list,
group_name)
group_management_print(NOT_IN_GROUP, not_in_group, contact_list,
group_name)
group_management_print(UNKNOWN_ACCOUNTS, rejected, contact_list,
group_name)
if removable and remaining and yes(
"Publish the list of removed members to remaining members?",
abort=False):
rem_packet = (GROUP_MSG_MEMBER_REM_HEADER + group.group_id +
int_to_bytes(len(remaining)) + b''.join(remaining) +
b''.join(removable))
queue_to_nc(rem_packet, queues[RELAY_PACKET_QUEUE])
def remove_contact(user_input: 'UserInput', window: 'TxWindow',
contact_list: 'ContactList', group_list: 'GroupList',
settings: 'Settings', queues: 'QueueDict',
master_key: 'MasterKey') -> None:
"""Remove contact from TFC."""
if settings.traffic_masking:
raise SoftError("Error: Command is disabled during traffic masking.",
head_clear=True)
try:
selection = user_input.plaintext.split()[1]
except IndexError:
raise SoftError("Error: No account specified.", head_clear=True)
if not yes(f"Remove contact '{selection}'?", abort=False, head=1):
raise SoftError("Removal of contact aborted.",
head=0,
delay=1,
tail_clear=True)
if selection in contact_list.contact_selectors():
onion_pub_key = contact_list.get_contact_by_address_or_nick(
selection).onion_pub_key
else:
if validate_onion_addr(selection):
raise SoftError("Error: Invalid selection.",
head=0,
delay=1,
tail_clear=True)
onion_pub_key = onion_address_to_pub_key(selection)
receiver_command = CONTACT_REM + onion_pub_key
queue_command(receiver_command, settings, queues)
with ignored(SoftError):
remove_logs(contact_list, group_list, settings, master_key,
onion_pub_key)
queues[KEY_MANAGEMENT_QUEUE].put((KDB_REMOVE_ENTRY_HEADER, onion_pub_key))
relay_command = UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_REM_CONTACT + onion_pub_key
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
target = determine_target(selection, onion_pub_key, contact_list)
if any([g.remove_members([onion_pub_key]) for g in group_list]):
m_print(f"Removed {target} from group(s).", tail=1)
check_for_window_deselection(onion_pub_key, window, group_list)
def group_rm_group(group_name: str,
contact_list: 'ContactList',
group_list: 'GroupList',
settings: 'Settings',
queues: 'QueueDict',
master_key: 'MasterKey',
_: Optional[bytes] = None) -> None:
"""Remove the group with its members."""
if not yes(f"Remove group '{group_name}'?", abort=False):
raise FunctionReturn("Group removal aborted.",
head=0,
delay=1,
tail_clear=True)
if group_name in group_list.get_list_of_group_names():
group_id = group_list.get_group(group_name).group_id
else:
try:
group_id = b58decode(group_name)
except ValueError:
raise FunctionReturn("Error: Invalid group name/ID.",
head_clear=True)
command = LOG_REMOVE + group_id
queue_command(command, settings, queues)
command = GROUP_DELETE + group_id
queue_command(command, settings, queues)
if group_list.has_group(group_name):
with ignored(FunctionReturn):
remove_logs(contact_list, group_list, settings, master_key,
group_id)
else:
raise FunctionReturn(
f"Transmitter has no group '{group_name}' to remove.")
group = group_list.get_group(group_name)
if not group.empty() and yes("Notify members about leaving the group?",
abort=False):
exit_packet = (GROUP_MSG_EXIT_GROUP_HEADER + group.group_id +
b''.join(group.get_list_of_member_pub_keys()))
queue_to_nc(exit_packet, queues[RELAY_PACKET_QUEUE])
group_list.remove_group_by_name(group_name)
raise FunctionReturn(f"Removed group '{group_name}'.",
head=0,
delay=1,
tail_clear=True,
bold=True)
def change_setting_value(setting: str, value: str,
relay_settings: Dict[str, bytes], queues: 'QueueDict',
contact_list: 'ContactList', group_list: 'GroupList',
settings: 'Settings', gateway: 'Gateway') -> None:
"""Change setting value in setting databases."""
if setting in gateway.settings.key_list:
gateway.settings.change_setting(setting, value)
else:
settings.change_setting(setting, value, contact_list, group_list)
receiver_command = CH_SETTING + setting.encode() + US_BYTE + value.encode()
queue_command(receiver_command, settings, queues)
if setting in relay_settings:
if setting == 'allow_contact_requests':
value = bool_to_bytes(settings.allow_contact_requests).decode()
relay_command = UNENCRYPTED_DATAGRAM_HEADER + relay_settings[
setting] + value.encode()
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
def wipe(settings: 'Settings',
queues: 'QueueDict',
gateway: 'Gateway'
) -> None:
"""\
Reset terminals, wipe all TFC user data from Source, Networked, and
Destination Computer, and power all three systems off.
The purpose of the wipe command is to provide additional protection
against physical attackers, e.g. in situation where a dissident gets
a knock on their door. By overwriting and deleting user data the
program prevents access to encrypted databases. Additional security
should be sought with full disk encryption (FDE).
Unfortunately, no effective tool for overwriting RAM currently exists.
However, as long as Source and Destination Computers use FDE and
DDR3 memory, recovery of sensitive data becomes impossible very fast:
https://www1.cs.fau.de/filepool/projects/coldboot/fares_coldboot.pdf
"""
if not yes("Wipe all user data and power off systems?", abort=False):
raise FunctionReturn("Wipe command aborted.", head_clear=True)
clear_screen()
for q in [COMMAND_PACKET_QUEUE, RELAY_PACKET_QUEUE]:
while queues[q].qsize() != 0:
queues[q].get()
queue_command(WIPE_USR_DATA, settings, queues)
if not settings.traffic_masking:
if settings.local_testing_mode:
time.sleep(0.8)
time.sleep(gateway.settings.data_diode_sockets * 2.2)
else:
time.sleep(gateway.settings.race_condition_delay)
relay_command = UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_WIPE_COMMAND
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
os.system(RESET)
def queue_delayer():
"""Place datagrams into queue after delay."""
time.sleep(delay)
queue_command(b'test', settings, queues)
time.sleep(delay)
queue_to_nc(
PUBLIC_KEY_DATAGRAM_HEADER + TFC_PUBLIC_KEY_LENGTH * b'a' +
nick_to_pub_key('Alice'), # 1
queues[RELAY_PACKET_QUEUE])
time.sleep(delay)
queue_to_nc(UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_WIPE_COMMAND,
queues[RELAY_PACKET_QUEUE]) # 2
time.sleep(delay)
queue_to_nc(UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_EXIT_COMMAND,
queues[RELAY_PACKET_QUEUE]) # 3
time.sleep(delay)
queues[KEY_MANAGEMENT_QUEUE].put((
KDB_ADD_ENTRY_HEADER,
LOCAL_PUBKEY, # 4
SYMMETRIC_KEY_LENGTH * b'a',
SYMMETRIC_KEY_LENGTH * b'a',
SYMMETRIC_KEY_LENGTH * b'a',
SYMMETRIC_KEY_LENGTH * b'a'))
time.sleep(delay)
queue_message(user_input, window, settings, queues) # 5
time.sleep(delay)
queue_message(user_input, window, settings, queues) # 6
time.sleep(delay)
queues[KEY_MANAGEMENT_QUEUE].put(
(KDB_ADD_ENTRY_HEADER, nick_to_pub_key('Alice'),
SYMMETRIC_KEY_LENGTH * b'a', SYMMETRIC_KEY_LENGTH * b'a',
SYMMETRIC_KEY_LENGTH * b'a', SYMMETRIC_KEY_LENGTH * b'a'))
time.sleep(delay)
queue_message(user_input, window, settings, queues) # 7
time.sleep(delay)
queue_message(user_input, window, settings, queues) # 8
time.sleep(delay)
queues[SENDER_MODE_QUEUE].put(settings)
def exchange_public_keys(
onion_pub_key: bytes,
tfc_public_key_user: bytes,
kdk_hash: bytes,
contact: 'Contact',
settings: 'Settings',
queues: 'QueueDict',
) -> bytes:
"""Exchange public keys with contact.
This function outputs the user's public key and waits for user to
enter the public key of the contact. If the User presses <Enter>,
the function will resend the users' public key to contact.
"""
public_key_packet = PUBLIC_KEY_DATAGRAM_HEADER + onion_pub_key + tfc_public_key_user
queue_to_nc(public_key_packet, queues[RELAY_PACKET_QUEUE])
while True:
try:
tfc_public_key_contact = get_b58_key(B58_PUBLIC_KEY, settings,
contact.short_address)
except ValueError as invalid_pub_key:
invalid_key = str(invalid_pub_key).encode()
# Do not send packet to Relay Program if the user has for some reason
# managed to embed the local key decryption key inside the public key.
substrings = split_to_substrings(invalid_key,
ENCODED_B58_KDK_LENGTH)
safe_string = not any(
blake2b(substring) == kdk_hash for substring in substrings)
if safe_string:
public_key_packet = (UNENCRYPTED_DATAGRAM_HEADER +
UNENCRYPTED_PUBKEY_CHECK + onion_pub_key +
invalid_key)
queue_to_nc(public_key_packet, queues[RELAY_PACKET_QUEUE])
continue
if tfc_public_key_contact == b'':
public_key_packet = PUBLIC_KEY_DATAGRAM_HEADER + onion_pub_key + tfc_public_key_user
queue_to_nc(public_key_packet, queues[RELAY_PACKET_QUEUE])
continue
return tfc_public_key_contact
def remove_contact(user_input: 'UserInput', window: 'TxWindow',
contact_list: 'ContactList', group_list: 'GroupList',
settings: 'Settings', queues: 'QueueDict',
master_key: 'MasterKey') -> None:
"""Remove contact from TFC."""
if settings.traffic_masking:
raise FunctionReturn(
"Error: Command is disabled during traffic masking.",
head_clear=True)
try:
selection = user_input.plaintext.split()[1]
except IndexError:
raise FunctionReturn("Error: No account specified.", head_clear=True)
if not yes(f"Remove contact '{selection}'?", abort=False, head=1):
raise FunctionReturn("Removal of contact aborted.",
head=0,
delay=1,
tail_clear=True)
if selection in contact_list.contact_selectors():
onion_pub_key = contact_list.get_contact_by_address_or_nick(
selection).onion_pub_key
else:
if validate_onion_addr(selection):
raise FunctionReturn("Error: Invalid selection.",
head=0,
delay=1,
tail_clear=True)
else:
onion_pub_key = onion_address_to_pub_key(selection)
receiver_command = CONTACT_REM + onion_pub_key
queue_command(receiver_command, settings, queues)
with ignored(FunctionReturn):
remove_logs(contact_list, group_list, settings, master_key,
onion_pub_key)
queues[KEY_MANAGEMENT_QUEUE].put((KDB_REMOVE_ENTRY_HEADER, onion_pub_key))
relay_command = UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_REM_CONTACT + onion_pub_key
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
if onion_pub_key in contact_list.get_list_of_pub_keys():
contact = contact_list.get_contact_by_pub_key(onion_pub_key)
target = f"{contact.nick} ({contact.short_address})"
contact_list.remove_contact_by_pub_key(onion_pub_key)
m_print(f"Removed {target} from contacts.", head=1, tail=1)
else:
target = f"{selection[:TRUNC_ADDRESS_LENGTH]}"
m_print(f"Transmitter has no {target} to remove.", head=1, tail=1)
if any([g.remove_members([onion_pub_key]) for g in group_list]):
m_print(f"Removed {target} from group(s).", tail=1)
if window.type == WIN_TYPE_CONTACT:
if onion_pub_key == window.uid:
window.deselect()
if window.type == WIN_TYPE_GROUP:
for c in window:
if c.onion_pub_key == onion_pub_key:
window.update_window(group_list)
# If the last member of the group is removed, deselect
# the group. Deselection is not done in
# update_group_win_members because it would prevent
# selecting the empty group for group related commands
# such as notifications.
if not window.window_contacts:
window.deselect()
def add_new_contact(contact_list: 'ContactList', group_list: 'GroupList',
settings: 'Settings', queues: 'QueueDict',
onion_service: 'OnionService') -> None:
"""Prompt for contact account details and initialize desired key exchange.
This function requests the minimum amount of data about the
recipient as possible. The TFC account of contact is the same as the
Onion URL of contact's v3 Tor Onion Service. Since the accounts are
random and hard to remember, the user has to choose a nickname for
their contact. Finally, the user must select the key exchange method:
ECDHE for convenience in a pre-quantum world, or PSK for situations
where physical key exchange is possible, and ciphertext must remain
secure even after sufficient QTMs are available to adversaries.
Before starting the key exchange, Transmitter Program exports the
public key of contact's Onion Service to Relay Program on their
Networked Computer so that a connection to the contact can be
established.
"""
try:
if settings.traffic_masking:
raise SoftError(
"Error: Command is disabled during traffic masking.",
head_clear=True)
if len(contact_list) >= settings.max_number_of_contacts:
raise SoftError(
f"Error: TFC settings only allow {settings.max_number_of_contacts} accounts.",
head_clear=True)
m_print("Add new contact", head=1, bold=True, head_clear=True)
m_print([
"Your TFC account is", onion_service.user_onion_address, '',
"Warning!", "Anyone who knows this account",
"can see when your TFC is online"
],
box=True)
contact_address = get_onion_address_from_user(
onion_service.user_onion_address, queues)
onion_pub_key = onion_address_to_pub_key(contact_address)
contact_nick = box_input(
"Contact nick",
expected_len=
ONION_ADDRESS_LENGTH, # Limited to 255 but such long nick is unpractical.
validator=validate_nick,
validator_args=(contact_list, group_list, onion_pub_key)).strip()
key_exchange = box_input(f"Key exchange ([{ECDHE}],PSK) ",
default=ECDHE,
expected_len=28,
validator=validate_key_exchange).strip()
relay_command = UNENCRYPTED_DATAGRAM_HEADER + UNENCRYPTED_ADD_NEW_CONTACT + onion_pub_key
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
if key_exchange.upper() in ECDHE:
start_key_exchange(onion_pub_key, contact_nick, contact_list,
settings, queues)
elif key_exchange.upper() in PSK:
create_pre_shared_key(onion_pub_key, contact_nick, contact_list,
settings, onion_service, queues)
except (EOFError, KeyboardInterrupt):
raise SoftError("Contact creation aborted.",
head=2,
delay=1,
tail_clear=True)
def start_key_exchange(
onion_pub_key: bytes, # Public key of contact's v3 Onion Service
nick: str, # Contact's nickname
contact_list: 'ContactList', # Contact list object
settings: 'Settings', # Settings object
queues: 'QueueDict' # Dictionary of multiprocessing queues
) -> None:
"""Start X448 key exchange with the recipient.
This function first creates the X448 key pair. It then outputs the
public key to Relay Program on Networked Computer, that passes the
public key to contact's Relay Program. When contact's public key
reaches the user's Relay Program, the user will manually copy the
key into their Transmitter Program.
The X448 shared secret is used to create unidirectional message and
header keys, that will be used in forward secret communication. This
is followed by the fingerprint verification where the user manually
authenticates the public key.
Once the fingerprint has been accepted, this function will add the
contact/key data to contact/key databases, and export that data to
the Receiver Program on Destination Computer. The transmission is
encrypted with the local key.
---
TFC provides proactive security by making fingerprint verification
part of the key exchange. This prevents the situation where the
users don't know about the feature, and thus helps minimize the risk
of MITM attack.
The fingerprints can be skipped by pressing Ctrl+C. This feature is
not advertised however, because verifying fingerprints the only
strong way to be sure TFC is not under MITM attack. When
verification is skipped, TFC marks the contact's X448 keys as
"Unverified". The fingerprints can later be verified with the
`/verify` command: answering `yes` to the question on whether the
fingerprints match, marks the X448 keys as "Verified".
Variable naming:
tx = user's key rx = contact's key fp = fingerprint
mk = message key hk = header key
"""
if not contact_list.has_pub_key(onion_pub_key):
contact_list.add_contact(onion_pub_key, nick,
bytes(FINGERPRINT_LENGTH),
bytes(FINGERPRINT_LENGTH), KEX_STATUS_PENDING,
settings.log_messages_by_default,
settings.accept_files_by_default,
settings.show_notifications_by_default)
contact = contact_list.get_contact_by_pub_key(onion_pub_key)
# Generate new private key or load cached private key
if contact.tfc_private_key is None:
tfc_private_key_user = X448.generate_private_key()
else:
tfc_private_key_user = contact.tfc_private_key
try:
tfc_public_key_user = X448.derive_public_key(tfc_private_key_user)
# Import public key of contact
while True:
public_key_packet = PUBLIC_KEY_DATAGRAM_HEADER + onion_pub_key + tfc_public_key_user
queue_to_nc(public_key_packet, queues[RELAY_PACKET_QUEUE])
tfc_public_key_contact = get_b58_key(B58_PUBLIC_KEY, settings,
contact.short_address)
if tfc_public_key_contact != b'':
break
# Validate public key of contact
if len(tfc_public_key_contact) != TFC_PUBLIC_KEY_LENGTH:
m_print([
"Warning!", "Received invalid size public key.",
"Aborting key exchange for your safety."
],
bold=True,
tail=1)
raise FunctionReturn("Error: Invalid public key length",
output=False)
if tfc_public_key_contact == bytes(TFC_PUBLIC_KEY_LENGTH):
# The public key of contact is zero with negligible probability,
# therefore we assume such key is malicious and attempts to set
# the shared key to zero.
m_print([
"Warning!", "Received a malicious zero-public key.",
"Aborting key exchange for your safety."
],
bold=True,
tail=1)
raise FunctionReturn("Error: Zero public key", output=False)
# Derive shared key
dh_shared_key = X448.shared_key(tfc_private_key_user,
tfc_public_key_contact)
# Domain separate unidirectional keys from shared key by using public
# keys as message and the context variable as personalization string.
tx_mk = blake2b(tfc_public_key_contact,
dh_shared_key,
person=b'message_key',
digest_size=SYMMETRIC_KEY_LENGTH)
rx_mk = blake2b(tfc_public_key_user,
dh_shared_key,
person=b'message_key',
digest_size=SYMMETRIC_KEY_LENGTH)
tx_hk = blake2b(tfc_public_key_contact,
dh_shared_key,
person=b'header_key',
digest_size=SYMMETRIC_KEY_LENGTH)
rx_hk = blake2b(tfc_public_key_user,
dh_shared_key,
person=b'header_key',
digest_size=SYMMETRIC_KEY_LENGTH)
# Domain separate fingerprints of public keys by using the
# shared secret as key and the context variable as
# personalization string. This way entities who might monitor
# fingerprint verification channel are unable to correlate
# spoken values with public keys that they might see on RAM or
# screen of Networked Computer: Public keys can not be derived
# from the fingerprints due to preimage resistance of BLAKE2b,
# and fingerprints can not be derived from public key without
# the X448 shared secret. Using the context variable ensures
# fingerprints are distinct from derived message and header keys.
tx_fp = blake2b(tfc_public_key_user,
dh_shared_key,
person=b'fingerprint',
digest_size=FINGERPRINT_LENGTH)
rx_fp = blake2b(tfc_public_key_contact,
dh_shared_key,
person=b'fingerprint',
digest_size=FINGERPRINT_LENGTH)
# Verify fingerprints
try:
if not verify_fingerprints(tx_fp, rx_fp):
m_print([
"Warning!", "Possible man-in-the-middle attack detected.",
"Aborting key exchange for your safety."
],
bold=True,
tail=1)
raise FunctionReturn("Error: Fingerprint mismatch",
delay=2.5,
output=False)
kex_status = KEX_STATUS_VERIFIED
except (EOFError, KeyboardInterrupt):
m_print([
"Skipping fingerprint verification.", '', "Warning!",
"Man-in-the-middle attacks can not be detected",
"unless fingerprints are verified! To re-verify",
"the contact, use the command '/verify'.", '',
"Press <enter> to continue."
],
manual_proceed=True,
box=True,
head=2)
kex_status = KEX_STATUS_UNVERIFIED
# Send keys to the Receiver Program
c_code = blake2b(onion_pub_key, digest_size=CONFIRM_CODE_LENGTH)
command = (KEY_EX_ECDHE + onion_pub_key + tx_mk + rx_mk + tx_hk +
rx_hk + str_to_bytes(nick))
queue_command(command, settings, queues)
while True:
purp_code = ask_confirmation_code('Receiver')
if purp_code == c_code.hex():
break
elif purp_code == '':
phase("Resending contact data", head=2)
queue_command(command, settings, queues)
phase(DONE)
print_on_previous_line(reps=5)
else:
m_print("Incorrect confirmation code.", head=1)
print_on_previous_line(reps=4, delay=2)
# Store contact data into databases
contact.tfc_private_key = None
contact.tx_fingerprint = tx_fp
contact.rx_fingerprint = rx_fp
contact.kex_status = kex_status
contact_list.store_contacts()
queues[KEY_MANAGEMENT_QUEUE].put(
(KDB_ADD_ENTRY_HEADER, onion_pub_key, tx_mk, csprng(), tx_hk,
csprng()))
m_print(f"Successfully added {nick}.",
bold=True,
tail_clear=True,
delay=1,
head=1)
except (EOFError, KeyboardInterrupt):
contact.tfc_private_key = tfc_private_key_user
raise FunctionReturn("Key exchange interrupted.",
tail_clear=True,
delay=1,
head=2)
def new_local_key(contact_list: 'ContactList', settings: 'Settings',
queues: 'QueueDict') -> None:
"""Run local key exchange protocol.
Local key encrypts commands and data sent from Source Computer to
user's Destination Computer. The key is delivered to Destination
Computer in packet encrypted with an ephemeral, symmetric, key
encryption key.
The check-summed Base58 format key decryption key is typed to
Receiver Program manually. This prevents local key leak in following
scenarios:
1. CT is intercepted by an adversary on compromised Networked
Computer, but no visual eavesdropping takes place.
2. CT is not intercepted by an adversary on Networked Computer,
but visual eavesdropping records key decryption key.
3. CT is delivered from Source Computer to Destination Computer
directly (bypassing compromised Networked Computer), and
visual eavesdropping records key decryption key.
Once the correct key decryption key is entered to Receiver Program,
it will display the 2-hexadecimal confirmation code generated by
the Transmitter Program. The code will be entered back to
Transmitter Program to confirm the user has successfully delivered
the key decryption key.
The protocol is completed with Transmitter Program sending
LOCAL_KEY_RDY signal to the Receiver Program, that then moves to
wait for public keys from contact.
"""
try:
if settings.traffic_masking and contact_list.has_local_contact():
raise FunctionReturn(
"Error: Command is disabled during traffic masking.",
head_clear=True)
m_print("Local key setup", bold=True, head_clear=True, head=1, tail=1)
if not contact_list.has_local_contact():
time.sleep(0.5)
key = csprng()
hek = csprng()
kek = csprng()
c_code = os.urandom(CONFIRM_CODE_LENGTH)
local_key_packet = LOCAL_KEY_DATAGRAM_HEADER + encrypt_and_sign(
plaintext=key + hek + c_code, key=kek)
# Deliver local key to Destination computer
nc_bypass_msg(NC_BYPASS_START, settings)
queue_to_nc(local_key_packet, queues[RELAY_PACKET_QUEUE])
while True:
print_key("Local key decryption key (to Receiver)", kek, settings)
purp_code = ask_confirmation_code('Receiver')
if purp_code == c_code.hex():
nc_bypass_msg(NC_BYPASS_STOP, settings)
break
elif purp_code == '':
phase("Resending local key", head=2)
queue_to_nc(local_key_packet, queues[RELAY_PACKET_QUEUE])
phase(DONE)
print_on_previous_line(
reps=(9 if settings.local_testing_mode else 10))
else:
m_print([
"Incorrect confirmation code. If Receiver did not receive",
"the encrypted local key, resend it by pressing <Enter>."
],
head=1)
print_on_previous_line(
reps=(9 if settings.local_testing_mode else 10), delay=2)
# Add local contact to contact list database
contact_list.add_contact(LOCAL_PUBKEY, LOCAL_NICK,
bytes(FINGERPRINT_LENGTH),
bytes(FINGERPRINT_LENGTH),
KEX_STATUS_LOCAL_KEY, False, False, False)
# Add local contact to keyset database
queues[KEY_MANAGEMENT_QUEUE].put(
(KDB_ADD_ENTRY_HEADER, LOCAL_PUBKEY, key, csprng(), hek, csprng()))
# Notify Receiver that confirmation code was successfully entered
queue_command(LOCAL_KEY_RDY, settings, queues)
m_print("Successfully completed the local key exchange.",
bold=True,
tail_clear=True,
delay=1,
head=1)
os.system(RESET)
except (EOFError, KeyboardInterrupt):
raise FunctionReturn("Local key setup aborted.",
tail_clear=True,
delay=1,
head=2)
def change_setting(user_input: 'UserInput', window: 'TxWindow',
contact_list: 'ContactList', group_list: 'GroupList',
settings: 'Settings', queues: 'QueueDict',
master_key: 'MasterKey', gateway: 'Gateway') -> None:
"""Change setting on Transmitter and Receiver Program."""
# Validate the KV-pair
try:
setting = user_input.plaintext.split()[1]
except IndexError:
raise FunctionReturn("Error: No setting specified.", head_clear=True)
if setting not in (settings.key_list + gateway.settings.key_list):
raise FunctionReturn(f"Error: Invalid setting '{setting}'.",
head_clear=True)
try:
value = user_input.plaintext.split()[2]
except IndexError:
raise FunctionReturn("Error: No value for setting specified.",
head_clear=True)
# Check if the setting can be changed
relay_settings = dict(
serial_error_correction=UNENCRYPTED_EC_RATIO,
serial_baudrate=UNENCRYPTED_BAUDRATE,
allow_contact_requests=UNENCRYPTED_MANAGE_CONTACT_REQ)
if settings.traffic_masking and (setting in relay_settings
or setting == 'max_number_of_contacts'):
raise FunctionReturn(
"Error: Can't change this setting during traffic masking.",
head_clear=True)
if setting in ['use_serial_usb_adapter', 'built_in_serial_interface']:
raise FunctionReturn(
"Error: Serial interface setting can only be changed manually.",
head_clear=True)
if setting == 'ask_password_for_log_access':
try:
authenticated = master_key.load_master_key(
) == master_key.master_key
except (EOFError, KeyboardInterrupt):
raise FunctionReturn(f"Setting change aborted.",
tail_clear=True,
head=2,
delay=1)
if not authenticated:
raise FunctionReturn("Error: No permission to change setting.",
head_clear=True)
# Change the setting
if setting in gateway.settings.key_list:
gateway.settings.change_setting(setting, value)
else:
settings.change_setting(setting, value, contact_list, group_list)
receiver_command = CH_SETTING + setting.encode() + US_BYTE + value.encode()
queue_command(receiver_command, settings, queues)
if setting in relay_settings:
if setting == 'allow_contact_requests':
value = bool_to_bytes(settings.allow_contact_requests).decode()
relay_command = UNENCRYPTED_DATAGRAM_HEADER + relay_settings[
setting] + value.encode()
queue_to_nc(relay_command, queues[RELAY_PACKET_QUEUE])
# Propagate the effects of the setting
if setting == 'max_number_of_contacts':
contact_list.store_contacts()
queues[KEY_MANAGEMENT_QUEUE].put((KDB_UPDATE_SIZE_HEADER, settings))
if setting in ['max_number_of_group_members', 'max_number_of_groups']:
group_list.store_groups()
if setting == 'traffic_masking':
queues[SENDER_MODE_QUEUE].put(settings)
queues[TRAFFIC_MASKING_QUEUE].put(settings.traffic_masking)
window.deselect()
if setting == 'log_file_masking':
queues[LOGFILE_MASKING_QUEUE].put(settings.log_file_masking)