When someone who sounds like your mother calls in a panic asking for bail money, Signet lets you verify it's actually her.

Each paired contact generates a rotating 4-word phrase that only the real person's phone can produce. You ask her to read her phrase aloud; you type what you hear. Green banner: verified. Red banner: something's wrong — hang up and call her back on a number you already trust.

Signet works over any channel. Voice calls, video calls, text, email, in person, from across the country, from inside a locked hospital room. The only requirement is that the two of you paired once, in person or over a trusted channel, before the crisis.

Built for a world where AI voice cloning is commodity and social-engineering vishing attacks are industrialised. Defends against:

• Real-time voice deepfakes (ElevenLabs-class and up)
• Real-time video deepfakes in calls
• Pre-recorded deepfake voicemails
• Vishing using scraped biographical knowledge
• Compromised messaging accounts where the attacker has chat history but not the paired device
• SIM swaps (your secret is device-local, not phone-number-bound)
• "Reflection" attacks where the caller asks you to read your phrase first — the rotating code is direction-aware, so echoing it back fails by construction

Core properties:

• No server. No cloud. No account. The app has no INTERNET permission.
• No telemetry. No analytics. No ads. Not now, not ever.
• Hardware-backed secrets via Android Keystore. StrongBox when your device supports it.
• Offline-first by design. Airplane mode doesn't affect any flow.
• RFC-validated crypto: X25519 / HKDF-SHA-256 / AES-256-GCM, all verified against published test vectors.
• Open source, AGPL-3.0.

What's in v0.3:

• In-person QR pairing
• Long-distance pairing via encrypted transport package (for journalists, activists, distributed teams — the 8-word unlock secret lives on a channel you already trust)
• Lost-phone recovery via printed paper or saved file
• Multi-relationship storage with in-person rekey
• Bulk backup: export every paired relationship in one encrypted file, restore on a new phone with one 8-word secret (phone-switch day, made easy)
• Challenge-response fallback (printable card for when the other side can't reach their phone)
• Liveness prompts for video calls (physical challenges a pre-recorded loop can't match)
• Screenshot + screen-recording blocking on sensitive screens
• First-run walkthrough + post-pair practice nudge

What's NOT in v0.3:

• Duress codes (gated on an abuse-analysis pass)
• Small-org shared verification (requires group-key agreement research)
• Automatic key rotation (manual rekey available)
• Cloud backup (out of scope forever — see the privacy policy)
• Account recovery (there is no account)

If you are an elderly person worried about grandchild-scam calls; a journalist worried about a source being impersonated; a finance employee worried about CEO-fraud wire-transfer calls; a custody parent worried about an impersonator calling a child's school — Signet is for you. It is a single primitive, done well, offline, with no ongoing relationship to any company.

If you want to know more about the threat model or verify our posture yourself, the whole codebase + documentation is at https://github.com/digital-grease/signet.
