nostr-double-ratchet

Rust implementation of the Double Ratchet protocol for Nostr, providing forward-secure end-to-end encrypted messaging.

Overview

Based on Signal's Double Ratchet with header encryption, this crate implements secure session management over Nostr events. Messages are encrypted using NIP-44 and the double ratchet algorithm ensures forward secrecy even if keys are compromised.

Features

• Double Ratchet encryption - Forward secrecy with automatic key rotation
• Out-of-order message handling - Skipped message keys cached for delivery flexibility
• Session persistence - Serialize/deserialize session state
• NIP-44 integration - Uses Nostr's standardized encryption
• Type-safe - Leverages enostr's Pubkey type

Usage

use nostr_double_ratchet::{Session, Result};
use nostr::Keys;

// Initialize sessions
let alice_keys = Keys::generate();
let bob_keys = Keys::generate();

let shared_secret = [0u8; 32]; // Exchange securely via invite mechanism

let mut alice = Session::init(
    bob_pubkey,
    alice_keys.secret_key().to_secret_bytes(),
    true,  // initiator
    shared_secret,
    Some("alice".to_string()),
)?;

let mut bob = Session::init(
    alice_pubkey,
    bob_keys.secret_key().to_secret_bytes(),
    false,  // responder
    shared_secret,
    Some("bob".to_string()),
)?;

// Send encrypted message
let event = alice.send("Hello Bob!".to_string())?;

// Receive and decrypt
let plaintext = bob.receive(&event)?;

Tests

Run the test suite:

cargo test -p nostr-double-ratchet

Tests cover:

• Session initialization (initiator/responder)
• Message encryption/decryption
• Multi-message conversations
• Out-of-order delivery
• Session persistence
• Consecutive messages with ratchet stepping

Architecture

• Session - Core double ratchet implementation
• SessionState - Serializable session state with all keys and counters
• Header - Message metadata (sequence number, next public key, chain length)
• Utilities - KDF using HKDF-SHA256, serialization helpers

Status

Core functionality complete. SessionManager and Invite mechanisms are stubs for future implementation.