Thought I'd share my three-year project with the community.
https://github.com/maqp/tfc
The tl;dr is TFC is an end-to-end encryption plugin for Pidgin IM client
where the TCB is split and separated on two isolated computers behind
unidirectional, data-diode enforced RS232 gateways. This configuration
prevents infiltration of malware to transmitter computer and
exfiltration of keys/pt from receiver computer. The networked computer
running Pidgin never has access to private keys or plaintexts.
The cipher is XSalsa20-Poly1305, where the symmetric key is either
pre-shared or exchanged with Curve25519 ECDHE. MACs provide deniable
authentication and PBKDF2-HMAC-SHA256 provides per-message forward
secrecy with hash-ratchet.
Key generation uses Linux kernel CSPRNG but also allows mixing in
entropy from a HWRNG sampled by Raspberry Pi via GPIO natively or over
SSH. (Both HWRNG and data diodes are free hardware design).
Group messaging is done by multi-casting messages to each recipient
provided all members have exchanged a key pair for private messaging.
The last feature I'd like to highlight is trickle connection where user
sends a constant stream of noise packets to recipient / group, inside
which messages can be delivered. Files can be sent to recipient(s) in
background during the conversation.
Written in Python, licensed under GPL. I hope you find it interesting.
Markus
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