VINAC-FM
Verified Identity via Near-field Acoustic Cryptography
The highest assurance verification layer in the SilentAuth stack. Proves physical device proximity using inaudible ultrasonic frequency modulation, bound to a cryptographic challenge — no extra hardware required.
The SilentAuth Verification Stack
VINAC-FM sits at the top of a layered defense model. Each layer is only invoked when the previous one is insufficient.
Invisible Pass
Risk scoring, fingerprinting, and behavioral analysis — no user friction
Challenge
Checkbox and slider challenges for elevated risk scores
Cryptographic PoW
Signed cryptographic proof-of-work for high-risk sessions
VINAC-FM
Acoustic proximity verification — physical presence required
How It Works
Five steps from challenge issuance to certificate delivery
Challenge Issued
Server issues a nonce-bound VINAC challenge tied to the active verification session. The challenge specifies the required frequency band and duration.
Acoustic Emission
The authenticating device emits a frequency-modulated ultrasonic pulse encoding the challenge nonce. The signal is imperceptible to human hearing.
Proximity Capture
A second microphone (or the same device's mic, for same-device binding) captures and decodes the ultrasonic signal, extracting the nonce.
Cryptographic Binding
The received nonce is signed with the device's attestation key and returned to the SilentAuth verifier alongside the original session token.
Certificate Issued
On signature verification and acoustic match, a short-lived VINAC certificate is issued and embedded in the session receipt — proving physical presence.
Use Cases
High-Value Transactions
Require physical device presence before authorizing wire transfers, crypto withdrawals, or large purchases
AI Agent Execution Gates
Bind execution permits to physical operator presence for critical AI agent actions
Infrastructure Changes
Prevent remote attackers from executing deployment or infrastructure mutations even with stolen credentials
Identity Binding
Confirm the physical human behind the digital session — not just their token
Regulatory Compliance
Meet SCA (Strong Customer Authentication) and physical presence requirements for PSD2, HIPAA, and SOC 2
Key Ceremony Operations
Require in-person presence for secret rotation, HSM access, and certificate authority operations
Protocol Specification Highlights
Integration
JavaScript SDK
import { SilentAuth } from '@silentauth/js';
const sa = new SilentAuth({ publicKey: 'pk_live_…' });
// Request VINAC-FM Layer 4 challenge
const { sessionId } = await sa.verification.create({
layers: [1, 2, 3, 4], // include VINAC
});
// Emit acoustic challenge
await sa.vinac.emitChallenge(sessionId, {
frequency: 'ultrasonic_18khz',
duration: 3000,
});
// Listen and capture on the same or nearby device
const proof = await sa.vinac.captureResponse(sessionId);
const receipt = await sa.verification.complete(proof);Device Requirements
Availability
VINAC-FM is available on the Business and Enterprise plans. Protocol v1.0 is in active development. See the roadmap →
VINAC-FM is the transport layer for Logos Lexicon
Logos Lexicon is the semantic intent protocol that runs above VINAC-FM. VINAC-FM proves the signal is physically legitimate; Logos Lexicon defines what that signal authorizes — through a closed vocabulary of pre-agreed semantic tokens resolved locally, with no instruction parsing or injection surface.
Learn about Logos LexiconThe last mile of identity assurance
When tokens, passwords, and behavioral signals are not enough — prove the human is physically present.