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 cipher crate.

This crate contains the following variants of the ChaCha20 core algorithm:

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: 192-bit extended nonce variant
XChaCha8 / XChaCha12: reduced round variants of XChaCha20

⚠️ Security Warning: Hazmat!

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

If in doubt, use the chacha20poly1305 crate instead, which provides an authenticated mode on top of ChaCha20.

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::cipher::{NewCipher, StreamCipher, StreamCipherSeek};

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]);