Crate chacha20

Expand description

The ChaCha20 stream cipher (RFC 8439)

ChaCha20 is a lightweight stream cipher which is amenable to fast, constant-time implementations in software. It improves upon the previous Salsa20 stream cipher, providing increased per-round diffusion with no cost to performance.

Cipher functionality is accessed using traits from re-exported stream-cipher crate.

This crate contains three variants of ChaCha20:

ChaCha20: standard IETF variant with 96-bit nonce
ChaCha20Legacy: (gated under the legacy feature) “djb” variant with 64-bit nonce
ChaCha8 / ChaCha12: reduced round variants of ChaCha20
XChaCha20: (gated under the xchacha20 feature) 192-bit extended nonce variant

Security Warning

This crate does not ensure ciphertexts are authentic, which can lead to serious vulnerabilities if used incorrectly!

USE AT YOUR OWN RISK!

Diagram

This diagram illustrates the ChaCha quarter round function. Each round consists of four quarter-rounds:

Legend:

⊞ add
‹‹‹ rotate
⊕ xor

Usage

use chacha20::{ChaCha20, Key, Nonce};
use chacha20::stream_cipher::{NewStreamCipher, SyncStreamCipher, SyncStreamCipherSeek};

let mut data = [1, 2, 3, 4, 5, 6, 7];

let key = Key::from_slice(b"an example very very secret key.");
let nonce = Nonce::from_slice(b"secret nonce");

// create cipher instance
let mut cipher = ChaCha20::new(&key, &nonce);

// apply keystream (encrypt)
cipher.apply_keystream(&mut data);
assert_eq!(data, [73, 98, 234, 202, 73, 143, 0]);

// seek to the keystream beginning and apply it again to the `data` (decrypt)
cipher.seek(0);
cipher.apply_keystream(&mut data);
assert_eq!(data, [1, 2, 3, 4, 5, 6, 7]);