xAirGap: Air-Gapped Key Exchange

The Problem

Key exchange protocols require electronic communication channels. In hostile environments, all electronic channels may be compromised, monitored, or unavailable. There is no standard protocol for bootstrapping cryptographic trust without electronics.

Diffie-Hellman, X25519, and every modern key agreement protocol assume a functioning electronic channel between parties. In embassies under surveillance, military field operations, or diplomatic contexts where SIGINT capabilities are assumed, this assumption fails catastrophically.

Manual key exchange via a single physical medium (USB drive, printed key) creates a single point of compromise. If the courier is intercepted, the entire key is exposed. There is no threshold protection, and there is no way to verify integrity without a pre-shared secret.

The Old Way

The PRIVATE.ME Solution

Both parties generate X25519 keypairs locally, split their public keys via Double XorIDA into QR shares, and exchange shares through independent physical couriers. Each party reconstructs the other's public key from K shares and derives the ECDH shared secret.

xAirGap eliminates the single-courier vulnerability by distributing public key material across multiple independent paths. An adversary must intercept K-of-N couriers to learn the public key -- and even then, they only have the public key, not the private key needed to derive the shared secret.

The protocol is bidirectional: both parties simultaneously distribute their public key shares to each other. Once both sides reconstruct, X25519 ECDH produces an identical shared secret on both ends without any electronic communication.

The New Way

How It Works

Symmetric bidirectional protocol: both parties independently generate, split, distribute, reconstruct, and derive. No coordination channel needed -- only pre-agreed courier logistics.

Use Cases

Integration

import { initiateExchange, completeExchange } from '@private.me/xairgap';

// Party A: generate keypair and split public key
const exchange = await initiateExchange(myKeypair, {
  n: 3,        // total QR shares
  k: 2,        // threshold to reconstruct
});

// exchange.shares[0..2] -- give to couriers
// Each courier carries one QR share to Party B

// Party A: receive K shares from Party B's couriers
const result = await completeExchange(myKeypair, receivedShares);
// result.sharedSecret -- X25519 ECDH derived

Security Properties

Verifiable Data Protection

Every operation in this ACI produces a verifiable audit trail via xProve. HMAC-chained integrity proofs let auditors confirm that data was split, stored, and reconstructed correctly — without accessing the data itself.

Ready to deploy xAirGap?

Talk to Ren, our AI sales engineer, or book a live demo with our team.

Ship Proofs, Not Source

xAirgap generates cryptographic proofs of correct execution without exposing proprietary algorithms. Verify integrity using zero-knowledge proofs — no source code required.

Use Cases