Technical documentation

For those who want to verify or reimplement. The full documents are in the code repository, in French and English.

Documents

Document	Contents
`sources/PROTOCOL.en.md`	The protocol: identity, contacts, messages, attachments, groups, multi-server, push, WebSocket transport.
`sources/ARCHITECTURE.en.md`	Components, cryptography, encrypted storage, database schema, security model and known limits.
`state.en.md`	Progress: what is done, tested, and what remains.
`sources/SERVER_INSTALLATION.en.md`	Setting up your own relay server, public or private (ASP.NET Core 10, nginx, systemd). `sources/DEPLOYMENT.en.md` gives the concrete example.
`sources/ADMINISTRATION.en.md`	Administering a relay or a push gateway without restarting: invitations, bans, sibling servers, logs, tracing.
`sources/DEPLOYMENT_PUSH.en.md`	Setting up the push gateway (one key per relay, maintenance, limits).
`sources/CONSOLE_ADMIN.en.md`	Web administration console (Pro edition): installation, roles, two-factor sign-in, audit.
`sources/diagrams/`	14 explanatory diagrams, in French and English.

Every document exists in French (.md) and English (.en.md), except the deployment guide, which is French only for now.

Cryptography at a glance

Use	Primitive
Identity (keys derived from 3 phrases)	Argon2id (32 MiB, t = 3), then HKDF-SHA256
Per-message key agreement	Ephemeral X25519, then HKDF-SHA256
Encryption	ChaCha20-Poly1305
Signature	Ed25519, bound to sender, recipient and message type
Groups	Shared key per epoch, renewed on every membership change
Attachments	48 KiB chunks, SHA-256 Merkle tree
Local database	SQLite encrypted with SQLCipher, key derived from the phrases
Server to server	HMAC-SHA256 signed requests, 120 s window, single-use nonce

Cryptography is implemented with BouncyCastle (managed code, portable to Android and iOS) and checked against fixed test vectors.

What the design protects, and what it does not

Protected

Message and attachment contents are end-to-end encrypted and signed; servers never see them.
The local database, private keys included, is encrypted at rest.
Excluding a group member prevents them from reading what follows (key renewal).
Every file chunk is checked against a hash an attacker cannot forge.
A server cannot impersonate a user: registration requires proof of possession of the key.

Accepted limits

Metadata: a server sees the sender, recipient, timestamps and connection times.
No ratchet: the recipient's long-term key decrypts past traffic if stolen. Losing your phrases loses the identity; stealing them steals it.
A dishonest group member can pass the current key to an excluded person, outside the protocol.
"Delete for everyone" and "edit" are best-effort: a modified client can ignore them, and the recipient may have copied the message before.
Received files are stored unencrypted in the app's protected space on the device.
Stolen phone: the PIN protects the screen, not the encryption. Remote wipe destroys the phone's copy but does not revoke the identity.

Report a vulnerability: contact@rebisway.com.

Hosting your own server

A relay server is an ASP.NET Core 10 application behind nginx. It stores no messages. A private server needs no registration: put its address in your contact card. A public server can pair with other public servers by exchanging a shared secret (an allow-list managed by hand). A private server may also accept only the people it invited. The step-by-step guide is sources/SERVER_INSTALLATION.en.md; day-to-day administration is in sources/ADMINISTRATION.en.md.

Reference server: https://fs.rebisway.com (Settings → Servers → add).

Moving a client to a sibling server — A client moving to a sibling server.

Notifications through several gateways — Notifications: several gateways and a circuit breaker.

Licence

FreeSpeech is free software. The code is published under the GNU AGPL v3 or later: you may study, modify and redistribute it under its terms. The server being a network service, anyone running a modified version must offer its source code to the users of that service. A separate commercial licence is available on request, to embed FreeSpeech in a product that cannot comply with the AGPL: contact@rebisway.com. The web administration console (Pro edition) is distributed separately; it only uses the servers' public admin APIs.