###Tinfoil Chat NaCl
TFC-NaCl is a high assurance encryption plugin for Pidgin IM client that protects users from passive eavesdropping, active MITM attacks and remote CNE (aka equipment interference) of endpoints practiced by TLAs such as the NSA, GCHQ and BKA.
###Overview
Strong end-to-end encryption with Curve25519 ECDHE / PSKs. XSalsa20-Poly1305 AEAD with forward secrecy and deniability.
Secure key generation with /dev/urandom mixed with entropy from open circuit design GPIO HWRNG of RPi that acts either as TCB itself or as a sampling device over SSH.
Endpoint security obtained with hardware-based TCB separation: Unidirectional data flow between end point's three computers prevents either injection of malware or exfiltration of keys and plaintexts from TCB regardless of existing software zero-day vulnerabilities in software.
Defeats metadata about quantity and schedule of communication with trickle connection that outputs constant stream of encrypted noise data.
Covert file transfer that takes place in background during trickle connection.
Multicasting of messages and files to multiple recipients (no trickle supported).
###How it works
TFC uses three computers per endpoint. Alice enters her commands and messages to program Tx.py running on her Transmitter computer (TxM), a TCB separated from network. Tx.py encrypts and signs plaintext data and relays it to receiver computers (RxM) via networked computer (NH) through RS-232 interface and a data diode.
Depending on packet type, the program NH.py running on Alice's NH forwards packets from TxM-side serial interface to Pidgin and local RxM (through another RS-232 interface and data diode). Local RxM authenticates and decrypts received data before processing it.
Pidgin sends the packet either directly or through Tor network to IM server, that then forwards it directly (or again through Tor) to Bob.
NH.py on Bob's NH receives Alice's packet from Pidgin, and forwards it through RS-232 interface and data diode to Bob's RxM, where the ciphertext is authenticated, decrypted, and processed. When the Bob responds, he will send the message/file using his TxM and in the end Alice reads the message from her RxM.
###Why keys can not be exfiltrated
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Malware that exploits an unknown vulnerability in RxM can infiltrate to the system, but is unable to exfiltrate keys or plaintexts, as data diode prevents all outbound traffic.
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Malware can not breach TxM as data diode prevents all inbound traffic. The only data input from RxM to TxM is the 72 char public key, manually typed by user.
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The NH is assumed to be compromised, but unencrypted data never touches it.
Optical repeater inside the optocoupler of the data diode (below) enforces direction of data transmission.
###Installation
###How to use
###More information
White paper and manual for previous versions are listed below. TFC-NaCl specific updates are listed in the updatelog. Updated white paper and documentation are under work.
White paper: https://cs.helsinki.fi/u/oottela/tfc.pdf