Secured Gibberlink: a signed agent message that travels as sound

What this proves, honestly

Two agents want to exchange "agent-b authorized a 12.50 USDC payment" over a channel neither of them controls: sound in the air. The receiver still has to answer two separate questions, did agent-b really say this and was it changed on the way. An RFC 9421 HTTP Message Signature answers both: the sender signs the method, authority, path, and a digest of the body with an Ed25519 key, so any edit breaks the signature and anyone with the sender's public key can check it offline.

The sound is real, not a metaphor. This page synthesizes the signed envelope into an audible ggwave waveform, plays it through your speaker, and decodes that same waveform back into the envelope. The envelope is larger than one audio frame, so it is chunked into seq:total:piece frames and reassembled on the other side, failing closed if a frame is missing.

The verifier is transport-independent. The exact same signed envelope verifies whether it arrived over HTTP or over sound. The receiver POSTs it to the live, deployed service POST https://verify.algovoi.co.uk/rfc9421 and shows you exactly what it returns. Nothing on this page is precomputed; the signature is generated fresh in your browser each run.

What the anchor does and does not do. The public key rides inside the envelope, so it is only as trustworthy as your knowledge of whose key it is. Binding a key to a named root (a DID or a domain) relocates trust to that root; it does not remove trust. This page proves the signature math and the acoustic hop; deciding that a given key really belongs to "agent-b" is a separate, out-of-band step. See the RFC 9421 Testbed for the plain-HTTP version of the same verifier.

No adoption numbers, no claims beyond what the live endpoint computes and what ggwave actually decodes when you press the button.

Run the handshake

Notes for running this page

• Data over sound is genuinely slow. ggwave moves roughly 8 to 16 bytes per second, so the ~0.75 KB signed envelope takes on the order of half a minute to transmit as audio. That is the real bandwidth of the channel, not a bug. Watch the frames go by; the verify at the end is instant.
• Speaker required for the audible hop. The in-page decode reads the same synthesized waveform the page plays, so it works even with the volume down, but you will hear the chirps if sound is on.
• Microphone mode is best-effort. A real acoustic hop between two devices depends on volume, distance, and room noise, and the browser must capture at 48 kHz. If permission is denied or capture fails, the page falls back to the in-page waveform so the demo still completes.
• CORS. The live endpoint allows browser fetch only from allowlisted origins (currently algovoi.co.uk and www.algovoi.co.uk). Served from there, the button works directly. Opened as a local file:// or from another host, the browser sends a disallowed origin and the live call is blocked; the signing and the sound hop still run and are shown.
• Verify is stateless and read-only. Nothing you do here changes any server state. The key is a throwaway generated per run and never leaves your browser except as the public key inside the envelope.

Bundled locally, no CDN: ggwave.js (MIT, wasm inlined) and nacl.min.js (TweetNaCl, public domain). SHA-256 is the browser's own SubtleCrypto.