1 unstable release
0.1.0 | Mar 8, 2019 |
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#1242 in Cryptography
Used in double-ratchet-signal
52KB
739 lines
Double Ratchet
A pure Rust implementation of the Double Ratchet, as specified by Trevor Perrin and Moxie Marlinspike.
The Double Ratchet allows two users to communicate securely: it provides its users with a confidential and authentic channel, which includes forward secrecy and future secrecy. After initialization with a shared secret key and an authenticated public key, the Double Ratchet will automatically handle all key management required to support this channel, which includes handling the decryption of messages that arrive out-of-order.
The Double Ratchet itself requires a public key crypto system that can perform
Diffie-Hellman (DH) operations, a secret key crypto system that provides
authenticated encryption with associated data (AEAD) and two key
derivation functions (KDF). This crate aims to be agnostic towards the
implementation of these functions: users of the crate implement the
CryptoProvider
trait and the DoubleRatchet
struct should take care of the
rest.[^1]
[^1]: But contact me if you have a use-case where the interface is not sufficient and I'll see if I can accommodate.
Examples
The following example corresponds to the way the Double Ratchet is used in the
Signal protocol. For more details about the implementation, see
tests/signal.rs
, which also supplies SignalCryptoProvider
. We assume
that Alice and Bob share a secret key SK
and Alice knows Bob's public
key.
use double_ratchet::{DoubleRatchet};
use rand_os::RandOs;
let mut rng = OsRng::new().unwrap();
type DR = DoubleRatchet<SignalCryptoProvider>;
// Alice intializes and sends the first message
let mut alice = DR::new_alice(&SK, bobs_public_prekey, None, &mut rng);
let pt0 = b"Hello Bob";
let (h0, ct0) = alice.ratchet_encrypt(pt0, b"A2B", &mut rng);
// Bob initializes and receives the first message
let mut bob = DR::new_bob(&SK, bobs_prekey_pair, None);
assert_eq!(
Ok(Vec::from(&pt0[..])),
bob.ratchet_decrypt(&h0, &ct0, b"A2B")
);
// After receiving the first message, Bob can send his replies
let pt1 = b"Hi Alice";
let (h1, ct1) = alice.ratchet_encrypt(pt1, b"B2A", &mut rng);
let pt2 = b"How are you?";
let (h2, ct2) = bob.ratchet_encrypt(pt2, b"B2A", &mut rng);
assert_eq!(
Ok(Vec::from(&pt_b_0[..])),
alice.ratchet_decrypt(&h_b_0, &ct_b_0, b"B2A")
);
// Note that Alice has not yet received Bob's first message...
let pt3 = b"Good and you?";
let (h3, ct3) = alice.ratchet_encrypt(pt3, b"A2B", &mut rng);
assert_eq!(
Ok(Vec::from(&pt3[..])),
bob.ratchet_decrypt(&h3, &ct3, b"A2B")
);
// ...but when she does get it she will be able to decrypt
assert_eq!(
Ok(Vec::from(&pt1[..])),
alice.ratchet_decrypt(&h1, &ct1, b"B2A")
);
Installation
The Double Ratchet crate is distributed through crates.io: install it
by adding the following to your Cargo.toml
:
[dependencies]
double-ratchet = "0.1"
Documentation
The documentation is available here.
Future plans
This isn't even my final form! I intend to add at least the following features and am open for suggestions for more features.
- a Header Encrypted variant of the Double Ratchet
- generalize the
KeyStore
to allow automatic deletion of very old keys - provide a way for saving/restoring a
DoubleRatchet
to storage
Dependencies
~64KB