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 account whose metadata can 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 **safety code** verification. You confirm a short code out of band before the session is trusted, which is what defeats a man in the middle.
- **A minimal invitation.** The code you hand over carries only what is needed to open the connection — roughly 110 to 150 bytes, one QR code. Keys and signatures no longer travel with it; they move over the connection itself, pinned by a commitment inside the invitation. See [The invitation](#the-invitation).
- **One-to-one voice and video calls** over the same verified connection. Media rides the 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 at 15 to 20 percent 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.
- **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.
1.**Peer A** creates an invitation, shareable as a QR code, a link or plain text. It is small enough to be a single QR code — point a camera at it and it is read in one go.
3. The two browsers finish the key exchange **over the connection they just opened**, not inside the invitation. Each side checks the other's keys against a fingerprint-sized commitment that was in the invitation before accepting them.
4. Both sides now show the same **safety code**. Compare it over something an attacker cannot impersonate: in person, or a voice you recognise.
5. The chat unlocks only after both people confirm the matching code. Three incorrect attempts end the session.
Step 4 is not a formality. Completing the key exchange proves that someone completed it, not who. Anyone able to intercept and rewrite the invitation can do that with both of you at once, and comparing the code is what catches it.
A session is **not** treated as verified until both peers complete the safety code comparison. 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.
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' addresses and traffic timing, though never message contents. See [`doc/USE-POLICY.md`](doc/USE-POLICY.md).
SecureBit is a progressive web app. 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. Read [`doc/CONTRIBUTING.md`](doc/CONTRIBUTING.md) for the workflow and [`doc/USE-POLICY.md`](doc/USE-POLICY.md) for what the project is and is not for.
