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Description:

Pyxolotl 0.2

Send and receive messages encrypted with Axolotl (Double Ratchet) protocol

Description
Pyxolotl allows you to send and receive secure end-to-end encrypted messages with
perfect forward and future secrecy over
any channel (email, IM, IRC, Twitter, Hangouts, Facebook, etc.). It uses same
Axolotl (Double Ratchet) protocol as Signal
messaging app by Open Whisper Systems.

Protocol
Actual wire protocol is described
here. Headers
(for differentiating between standard message and key exchange message) are obfuscated
with 100000 iterations of PBKDF2 (with whole encrypted message used as salt). This should make
identifying Pyxolotl messages very resource-intensive to impede mass surveillance or filtering.

Key exchange
Pyxolotl is serverless, all messages are sent P2P, so it doesn’t use
prekeys. You must first send initial key
exchange message to recipient and wait for his reply before sending actual message (this is same as
SMS Transport
in older versions of TextSecure and in SMSSecure / Silence). Once this initial key exchange is completed,
both parties can send messages to each other without any other inconveniences. Security model is
TOFU (Trust On First Use), both parties
should compare public keys via independent secure channel to mitigate potential MITM attack during
initial key exchange.

Transports
Pyxolotl have pluggable transports. For now there is only plaintext transport (which prints
encoded messages to terminal) and email transport (messages are encoded to / decoded from
well-formed MIME emails).

Encodings
Encrypted messages can use different transport encodings. For now there is standard Base64
encoding (without padding) and as a curiosity mnemonic encoding (based on
BIP-0039: Mnemonic code for generating deterministic keys
which encodes encrypted messages as a sequence of words). Mnemonic encoding is inefficient
(messages are about 3.5x larger than Base64), but it can add another layer of obfuscation against
mass surveillance or filtering.

Local encryption
Local database (private key, sessions, etc.) is encrypted with AES-CBC using 256-bit key derived
from passphrase (with 100000 iterations of PBKDF2 and random salt) and authenticated with HMAC-SHA256.

Requirements

Python >= 3.3
enum (https://pypi.python.org/pypi/enum) for Python < 3.4
python-axolotl (https://github.com/tgalal/python-axolotl)
python-axolotl-curve25519 (https://github.com/tgalal/python-axolotl-curve25519)
protobuf (https://github.com/google/protobuf) >= 2.6
pycrypto (https://github.com/dlitz/pycrypto)

Usage
Run pyxolotl --help to see all available options.

Help
usage: pyxolotl [-h] [-d] [-t {plaintext,email}] [-e {base64,mnemonic}]
[--log LOG] [--db DB] [--config CONFIG] [--version]
[-a ADDRESS] [-s SUBJECT]
{list,ls,send,receive,recv,exchange,delete,del,rm,passwd} ...

send and receive messages encrypted with Axolotl protocol

optional arguments:
-h, --help show this help message and exit
-d, --debug log detailed debugging messages (default: False)
-t {plaintext,email}, --transport {plaintext,email}
choose message transport (default: plaintext)
-e {base64,mnemonic}, --encoder {base64,mnemonic}
choose message encoding (default: base64)
--log LOG log file path (default:
~/.local/share/pyxolotl/pyxolotl.log)
--db DB database file path (default:
~/.local/share/pyxolotl/pyxolotl.db)
--config CONFIG configuration file path (default:
~/.local/share/pyxolotl/pyxolotl.json)
--version show program's version number and exit

email transport:
-a ADDRESS, --address ADDRESS
your own email address (default: None)
-s SUBJECT, --subject SUBJECT
subject of sent emails (default: None)

commands:
run `pyxolotl COMMAND --help` to see help message for specific command

{list,ls,send,receive,recv,exchange,delete,del,rm,passwd}
available commands
list (ls) list known identities
send send message to recipient
receive (recv) receive message from sender
exchange start initial key exchage with recipient
delete (del, rm) end session with recipient
passwd change passphrase to local storage

Todo:

write more transports (especially Google Hangouts, Twitter Direct Messages, Facebook Messenger,
IRC and XMPP)
make email transport more complete (sending with SMTP, receiving with IMAP IDLE)
create IM-like console UI (with asyncio and Urwid)
create IM-like Qt 5/QML based GUI
add support for multiple devices
add support for group messages
add support for verifying identity with question (using
socialist millionaire protocol)

Example
[alice@nsa.gov ~]$ pyxolotl exchange bob
SEND:
To: bob
Encrypted message: 4uJ8zyMIwSgSIQUuLKlC8WdspRietP45P6nFU6/50wT4cQYxNw4vvqKLHxohBYLC5sDLZ78syjQIMf9PA+3Q9MGootUvOajaZA3thspDIiEF6sSiWxB6l0B4oE7gcMl1T3W+hzI548U46cYrR5KUjXY

[bob@fsb.ru ~]$ pyxolotl receive
RECEIVE:
From: alice
Encrypted message: 4uJ8zyMIwSgSIQUuLKlC8WdspRietP45P6nFU6/50wT4cQYxNw4vvqKLHxohBYLC5sDLZ78syjQIMf9PA+3Q9MGootUvOajaZA3thspDIiEF6sSiWxB6l0B4oE7gcMl1T3W+hzI548U46cYrR5KUjXY

Received initial key exchange request! Send this reply to complete key exchange:
SEND:
To: alice
Encrypted message: 0yx89TMIwigSIQVN+wtEio0h+Zx7WPcIwM9WreOy0r7eETBclhOtDAvANhohBb4qfe8R05/167DQDdd2Gqp5OrxAPcriwJMtzi+2b7QrIiEFhfVGHlCm6b1SX36V1HeFX4pAeW15v1aLb2nGi57NZFAqQD3rKGjPDCCm1Kj6i8GUnf4MAc56fhRIYhUJH2mSvlcSAl2XotmR2Yz2lY0wa7TW1JnmUX+YBbIEgIHk0gQ9Log

[alice@nsa.gov ~]$ pyxolotl receive
RECEIVE:
From: bob
Encrypted message: 0yx89TMIwigSIQVN+wtEio0h+Zx7WPcIwM9WreOy0r7eETBclhOtDAvANhohBb4qfe8R05/167DQDdd2Gqp5OrxAPcriwJMtzi+2b7QrIiEFhfVGHlCm6b1SX36V1HeFX4pAeW15v1aLb2nGi57NZFAqQD3rKGjPDCCm1Kj6i8GUnf4MAc56fhRIYhUJH2mSvlcSAl2XotmR2Yz2lY0wa7TW1JnmUX+YBbIEgIHk0gQ9Log

Initial key exchange completed!

[alice@nsa.gov ~]$ pyxolotl ls
Your public key: 05eac4a25b107a974078a04ee070c9754f75be873239e3c538e9c62b4792948d76
Existing sessions:
Identity: bob, Pending key exchange: False
Public key: 0585f5461e50a6e9bd525f7e95d477855f8a40796d79bf568b6f69c68b9ecd6450

[bob@fsb.ru ~]$ pyxolotl ls
Your public key: 0585f5461e50a6e9bd525f7e95d477855f8a40796d79bf568b6f69c68b9ecd6450
Existing sessions:
Identity: alice, Pending key exchange: False
Public key: 05eac4a25b107a974078a04ee070c9754f75be873239e3c538e9c62b4792948d76

[alice@nsa.gov ~]$ pyxolotl send bob
Message: Hello Bob!
SEND:
To: bob
Encrypted message: a74TljMKIQWJl7sz1bTEIhF/7nwKBLRi7XeEpzcur7t/MOixAOfbHRAAGAAiEEgco7NQXppy/qsm5TdJllpW+nTQ1QjVsQ

[bob@fsb.ru ~]$ pyxolotl receive
RECEIVE:
From: alice
Encrypted message: a74TljMKIQWJl7sz1bTEIhF/7nwKBLRi7XeEpzcur7t/MOixAOfbHRAAGAAiEEgco7NQXppy/qsm5TdJllpW+nTQ1QjVsQ

DECRYPTED:
Hello Bob!

[bob@fsb.ru ~]$ pyxolotl send alice
Message: Hello Alice!
SEND:
To: alice
Encrypted message: Zd/HKjMKIQXLGyTr5AcvrpUhfR2H7bYqLXqVy7GpE84VvFFkm1LDbxAAGAAiEJDC8/kM59yVzNeCBtjDVOe1CHWuFDbhYg

[alice@nsa.gov ~]$ pyxolotl receive
RECEIVE:
From: bob
Encrypted message: Zd/HKjMKIQXLGyTr5AcvrpUhfR2H7bYqLXqVy7GpE84VvFFkm1LDbxAAGAAiEJDC8/kM59yVzNeCBtjDVOe1CHWuFDbhYg

DECRYPTED:
Hello Alice!