SecureBit.chat is a browser-based, peer-to-peer messenger built on **WebRTC** and the **Web Crypto API**. Two people establish a direct, end-to-end encrypted channel and verify each other in person — there is no registration, no central server relaying or storing messages, and no metadata account to leak. Everything cryptographic happens locally in the two browsers.
It is designed for people who need a small, auditable, zero-infrastructure way to talk privately: journalists and sources, security researchers, or anyone who simply wants a conversation that leaves nothing behind.
- **Double Ratchet forward secrecy** — every message is encrypted with its own key, and the session re-keys itself each time the conversation changes direction. See [Forward secrecy](#forward-secrecy).
- Interactive **Short Authentication String (SAS)** verification — you confirm a code out-of-band before the session is trusted, defeating man-in-the-middle attacks.
- Replay protection, message integrity (HMAC), and a live security report you can open at any time during a call.
- **1:1 voice and video calls** over the same verified peer-to-peer connection — media rides the SAS-verified DTLS-SRTP transport, so calls inherit the session's end-to-end encryption and never traverse a SecureBit server.
- **Adaptive audio**: Opus with in-band FEC, DTX and RED redundancy for intelligible speech under 15–20% packet loss; audio is prioritised and never throttled by the network controller.
- **Adaptive video**: VP9/AV1 single-encoding SVC (H.264/VP8 fallback) that degrades by spatial/temporal layer, with a runtime controller that trims video bitrate on loss/RTT and recovers as the link clears.
- **Live connection-quality indicator** (Excellent → Good → Fair → Weak) shown in the call UI, plus in-call mute and video-upgrade controls.
- **Encrypted voice messages** — record in the browser and send over the same end-to-end encrypted transfer channel as files. Audio is captured as PCM/WAV, integrity-protected by a signed hash, and played back inline on the recipient's device without ever touching disk.
- Run several independent chats at the same time. Every conversation gets its own encrypted session, keys and verification, so two chats can never mix.
- A side panel lists your open chats with unread badges. Switching is instant, and starting a new chat leaves the others connected.
- Set your availability (Available, Away, Busy or Invisible) and connected peers can see it. You can also give each chat a private label that is stored only on your device and is never sent to the other side.
A session is **not** treated as verified until both peers complete the SAS flow. This is the step that protects you against a man-in-the-middle: the code must be compared through a channel an attacker cannot impersonate. Until it is completed, the session will not act on control messages from the peer.
### Forward secrecy
Message protection does not rest on the keys agreed during the handshake. On top of them SecureBit runs the **Double Ratchet** — the design used by Signal:
- **Every message gets its own key.** It is derived from a chain key through a one-way function and discarded as soon as the message is encrypted or read, so keys held now cannot reconstruct earlier ones. Recovering the live state of a session does not expose what was said before.
- **Each change of direction re-keys the session.** Every reply introduces a fresh ECDH key pair and mixes a new shared secret into the root key, so the conversation continuously moves away from any state an attacker may have captured.
- **Out-of-order messages are handled within fixed bounds.** Keys are held for messages that have not arrived yet, capped at 512 per chain and 1024 in total and expiring after five minutes, with a limit on how far ahead a message may claim to be.
The ratchet is negotiated during the handshake and used when both peers support it. If one side is on an older release, the session falls back to per-session keys and the security panel reports which of the two is actually in use — it shows the state of your connection, not the capabilities of your client.
> SecureBit.chat is privacy software, not a guarantee. View-once and disappearing messages are cooperative (not screenshot-proof), and a TURN relay can observe both peers' IPs and traffic timing — though never message contents. See [`SECURITY_DISCLAIMER.md`](SECURITY_DISCLAIMER.md).
SecureBit is a PWA — open it in a supported browser and choose **Install** (or *Add to Home Screen* on mobile) to run it as a standalone, offline-capable app.
Incoming transfers require explicit consent. Metadata is validated and dangerous names rejected before the prompt appears. Accepted: common raster images, PDF, plain text, and ZIP. Executable/scriptable formats (`.exe`, `.bat`, `.sh`, `.js`, `.msi`, `.dmg`, `.jar`, `.ps1`, `.vbs`, `.html`, `.svg`, …) are blocked, and MIME type must agree with the file extension.
Issues and pull requests are welcome. SecureBit.chat is intended for lawful, ethical communication only — please read [`RESPONSIBLE_USE.md`](RESPONSIBLE_USE.md) before using or contributing.
