double-ratchet-2

Implementation of the double ratchet system/encryption as specified by Signal.

The implementation follows the cryptographic recommendations provided by Signal. The AEAD Algorithm uses a constant Nonce. This might be changed in the future.

Example Usage:

Standard:

use double_ratchet_2::ratchet::Ratchet;
use x25519_dalek::StaticSecret;

let sk = [1; 32];                                                 // Initial Key created by a symmetric key agreement protocol
let (mut bob_ratchet, public_key) = Ratchet::<StaticSecret>::init_bob(sk);        // Creating Bobs Ratchet (returns Bobs PublicKey)
let mut alice_ratchet = Ratchet::<StaticSecret>::init_alice(sk, public_key);      // Creating Alice Ratchet with Bobs PublicKey
let data = b"Hello World".to_vec();                               // Data to be encrypted
let ad = b"Associated Data";                                      // Associated Data

let (header, encrypted, nonce) = alice_ratchet.ratchet_encrypt(&data, ad);   // Encrypting message with Alice Ratchet (Alice always needs to send the first message)
let decrypted = bob_ratchet.ratchet_decrypt(&header, &encrypted, &nonce, ad); // Decrypt message with Bobs Ratchet
assert_eq!(data, decrypted)

With lost message:

use x25519_dalek::StaticSecret;

let sk = [1; 32];                                                 // Initial Key created by a symmetric key agreement protocol
let (mut bob_ratchet, public_key) = Ratchet::<StaticSecret>::init_bob(sk);        // Creating Bobs Ratchet (returns Bobs PublicKey)
let mut alice_ratchet = Ratchet::<StaticSecret>::init_alice(sk, public_key);      // Creating Alice Ratchet with Bobs PublicKey
let data = b"Hello World".to_vec();                               // Data to be encrypted
let ad = b"Associated Data";                                      // Associated Data

let (header1, encrypted1, nonce1) = alice_ratchet.ratchet_encrypt(&data, ad); // Lost message
let (header2, encrypted2, nonce2) = alice_ratchet.ratchet_encrypt(&data, ad); // Successful message

let decrypted2 = bob_ratchet.ratchet_decrypt(&header2, &encrypted2, &nonce2, ad); // Decrypting second message first
let decrypted1 = bob_ratchet.ratchet_decrypt(&header1, &encrypted1, &nonce1, ad); // Decrypting latter message

let comp = decrypted1 == data && decrypted2 == data;
assert!(comp);

Encryption before recieving inital message

use double_ratchet_2::ratchet::Ratchet;
use x25519_dalek::StaticSecret;
let sk = [1; 32];
let ad = b"Associated Data";
let (mut bob_ratchet, _) = Ratchet::<StaticSecret>::init_bob(sk);
let data = b"Hello World".to_vec();

let (_, _, _) = bob_ratchet.ratchet_encrypt(&data, ad);

Encryption after recieving initial message

However bob can (of course) also encrypt messages. This is possible, after decrypting the first message from alice.

use double_ratchet_2::ratchet::Ratchet;
use x25519_dalek::StaticSecret;
let sk = [1; 32];

let (mut bob_ratchet, public_key) = Ratchet::<StaticSecret>::init_bob(sk);
let mut alice_ratchet = Ratchet::<StaticSecret>::init_alice(sk, public_key);

let data = b"Hello World".to_vec();
let ad = b"Associated Data";

let (header1, encrypted1, nonce1) = alice_ratchet.ratchet_encrypt(&data, ad);
let _decrypted1 = bob_ratchet.ratchet_decrypt(&header1, &encrypted1, &nonce1, ad);

let (header2, encrypted2, nonce2) = bob_ratchet.ratchet_encrypt(&data, ad);
let decrypted2 = alice_ratchet.ratchet_decrypt(&header2, &encrypted2, &nonce2, ad);

assert_eq!(data, decrypted2);

Constructing and Deconstructing Headers

let header_bytes: Vec<u8> = header.concat(b"");
let header_const = Header::<x25519_dalek::PublicKey>::from(header_bytes.as_slice());
assert_eq!(header, header_const);

Example Ratchet with encrypted headers

use double_ratchet_2::ratchet::RatchetEncHeader;
use x25519_dalek::StaticSecret;
let sk = [0; 32];
let shared_hka = [1; 32];
let shared_nhkb = [2; 32];

let (mut bob_ratchet, public_key) = RatchetEncHeader::<StaticSecret>::init_bob(sk, shared_hka, shared_nhkb);
let mut alice_ratchet = RatchetEncHeader::<StaticSecret>::init_alice(sk, public_key, shared_hka, shared_nhkb);
let data = b"Hello World".to_vec();
let ad = b"Associated Data";

let (header, encrypted, nonce) = alice_ratchet.ratchet_encrypt(&data, ad);
let decrypted = bob_ratchet.ratchet_decrypt(&header, &encrypted, &nonce, ad);
assert_eq!(data, decrypted)

Export / Import Ratchet with encrypted headers

This ratchet implements import and export functionality. This works over a bincode backend and maybe useful for saving Ratchets to and loading from a file.

use x25519_dalek::StaticSecret;
let (bob_ratchet, public_key) = RatchetEncHeader::<StaticSecret>::init_bob(sk, shared_hka, shared_nhkb);
let ex_ratchet = bob_ratchet.export();
let im_ratchet = RatchetEncHeader::<StaticSecret>::import(&ex_ratchet).unwrap();
assert_eq!(im_ratchet.export(), bob_ratchet.export())

Features

Currently the crate only supports one feature: ring. If feature is enabled the crate switches to ring-compat and uses ring as backend for Sha512 Hashing. May result in slightly better performance.

TODO:

• Standard Double Ratchet
• Double Ratchet with encrypted headers

Current version: 0.4.0-pre.1

License: MIT