Julius Joska
6f9b08e844
UnifiedPush only exists on Android. On iOS getDistributor() and getDistributors() throw UnimplementedError, which surfaced as an uncaught error from the Push tile in Settings. Report an empty state instead.
Šepot
Šepot is an end-to-end encrypted messenger with anonymous, on-device identity. There is no phone number, e-mail, or password: an account is a keypair generated on the device, your ID is the fingerprint of your public key, and the only backup is a mnemonic phrase.
The design goal is metadata minimization with a public threat model — never "zero metadata". The relay is deliberately dumb: it cannot read message content, does not learn who sent a message, and does not log IP addresses. What it does see is documented honestly below.
Status: 1.2.x. Android is on Google Play (production 1.1.2, 1.2.0 in internal testing); iOS builds run through TestFlight. See
CHANGELOG.md.
Features
- Signal-grade cryptography via the official Rust
libsignal: X3DH + post-quantum PQXDH (Kyber-1024) key agreement, Double Ratchet, and sealed sender. - Anonymous identity — no phone/e-mail/password. Recovery through a 24-word mnemonic that encodes the identity key itself (not a KDF seed).
- Encrypted at rest — all local data lives in SQLCipher, unlocked by a PIN (Argon2id-derived key) or biometrics. Optional duress PIN opens a separate empty database.
- Group chats — up to 128 members, pairwise fan-out so every member gets full forward secrecy; the relay never learns a group exists.
- Attachments — images and files are encrypted client-side (AES-256-GCM) and uploaded as opaque blobs with a TTL; image metadata (EXIF/GPS) is stripped on send.
- Disappearing messages, read receipts (off by default), voice messages, replies, reactions, edits, contact verification (safety numbers).
- Push with or without Google — UnifiedPush/ntfy when a distributor is installed, otherwise FCM on Android (default since 1.2.0, can be switched off) and APNs on iOS. A push wake-up never carries content, sender, or count.
- Tor transport (Android, via Orbot) — routes relay traffic over a
.onionto hide the client IP. Off by default. - Five languages — Czech, English, German, Russian, Italian. The UI follows the system language and can be overridden in Settings.
How it works
┌────────────┐ sealed-sender ciphertext ┌──────────────┐
│ Šepot app │ ───────(WSS or Tor)─────────▶ │ relay │ ──▶ PostgreSQL
│ (Flutter) │ ◀────── wake push ─────────── │ (Rust/axum) │ (no content,
└────────────┘ └──────────────┘ no IP, no PII)
libsignal (FFI) offline queue, TTL
SQLCipher at rest opaque attachment blobs
Every message is encrypted end-to-end with libsignal and wrapped in a sealed-sender envelope, so the relay routes by recipient delivery address without learning the sender. Undelivered messages sit in a per-recipient queue with a fixed TTL and are hard-deleted on acknowledgement.
What the relay can see: the recipient's delivery address, message size, and timing. What it cannot see: message content, the sender's identity, group membership, or (with logging disabled as shipped) client IP addresses. The full model — including where the trust boundary sits — is in THIRD-PARTY-NOTICES.md and the crypto facade app/lib/core/crypto/.
Repository layout
| Path | Contents |
|---|---|
app/ |
Flutter client (Android, iOS; desktop scaffolding present) |
rust/ |
Cargo workspace — sepot-relay (relay server), sepot-proto (prost wire types) |
proto/ |
Protobuf wire definitions — single source for both Rust and Dart |
deploy/ |
Docker Compose for self-hosting the relay (with an optional Tor onion) |
tool/ |
Helper scripts (protobuf codegen for Dart) |
Building
Client (Android)
cd app
flutter pub get
flutter build apk --release
The native libsignal binary is fetched by the Flutter native-assets hook at build time. To point a dev build at your own relay:
flutter build apk --dart-define=SEPOT_RELAY=http://<dev-relay-host>:8470
Release signing reads app/android/key.properties (kept out of the repo); without it the build falls back to the debug signing config so flutter run still works. FCM is optional — the google-services plugin is only applied if you supply your own app/android/app/google-services.json (copy google-services.json.example). Without it the app runs on UnifiedPush.
Relay (self-host)
See deploy/relay/README.md. The relay is a single Rust binary plus PostgreSQL; put a TLS-terminating reverse proxy in front of it and, optionally, expose it as a Tor onion service.
Languages
UI strings live in app/lib/l10n/app_*.arb (cs, en, de, ru, it) and are compiled by Flutter's gen-l10n. Contributions of new translations are welcome — add an app_<locale>.arb, translate the keys from app_cs.arb, and run flutter gen-l10n.
Security
Cryptography is implemented by Signal's libsignal, not by hand-rolled primitives. If you find a vulnerability, please report it privately to security@sepot.cz rather than opening a public issue — see SECURITY.md and /.well-known/security.txt.
License
Šepot is licensed under the GNU Affero General Public License v3.0 — see LICENSE.
The license includes an AGPL §7 additional permission for app-store distribution: Šepot may be distributed through App Store / Google Play provided the complete corresponding source stays available under the AGPL through a channel without those store restrictions (this repository and the direct APK releases). That permission covers only Šepot's own code. The bundled Signal libsignal is AGPL-3.0 held by Signal Messenger, LLC — its app-store status is documented in THIRD-PARTY-NOTICES.md.