Deaddrop: Physical Dead Drop Messaging

The Problem

Digital communications leave metadata trails. Even end-to-end encrypted messaging reveals sender, recipient, timing, and frequency. No truly air-gapped messaging protocol exists for high-threat environments.

Signal, WhatsApp, and every encrypted messenger require electronic communication channels that produce metadata. Intelligence agencies, hostile governments, and sophisticated adversaries can exploit metadata — who talked to whom, when, and how often — without ever decrypting content.

Physical dead drops have existed for centuries, but they suffer from single-point-of-failure: if the drop location is compromised, the entire message is exposed. There is no threshold protection, no fault tolerance, and no cryptographic integrity verification.

The Old Way

The PRIVATE.ME Solution

Messages are AES-256-GCM encrypted, then split via Double XorIDA into QR shares placed at K separate physical locations. Single-use nonces via NonceStore prevent re-scanning. No electronics required for the drop itself. HMAC verification ensures integrity before reconstruction.

Deaddrop transforms the dead drop from a single-point vulnerability into a distributed threshold system. The sender places QR shares at independent locations. The recipient collects K shares from different sites. No single location contains enough information to reconstruct.

The NonceStore ensures each share is single-use: once scanned, the nonce is consumed and the share cannot be replayed. This prevents adversaries from covertly scanning and re-placing shares without detection. Each share carries an HMAC-SHA256 tag for tamper detection before reconstruction.

The New Way

How It Works

Five-step protocol: encrypt, split, place, collect, reconstruct. Every step is designed for air-gapped operation with no electronic communication between sender and recipient.

Use Cases

Integration

import { createDeadDrop, retrieveMessage } from '@private.me/deaddrop';

// Create a dead drop with 3 shares, 2 required
const drop = await createDeadDrop(messageBuffer, recipientDid, {
  n: 3,        // total QR shares
  k: 2,        // threshold to reconstruct
});

// drop.shares[0..2] -- place at separate locations
// Each share has HMAC tag + single-use nonce

// Recipient: scan K shares from drop sites
const message = await retrieveMessage(scannedShares);
// HMAC verified before reconstruction

# Start deaddrop-cli server on port 4000
deaddrop-cli start --port 4000

# Create drop via HTTP endpoint
curl -X POST http://localhost:4000/create \
  -H "Content-Type: application/json" \
  -d '{
    "message": "...",
    "recipientDid": "did:key:z6Mk...",
    "n": 3,
    "k": 2
  }'

# Returns QR-printable shares with single-use nonces

Implementation Status

Security Properties

Performance & Guarantees

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 Deaddrop?

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