Crate chacha20

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: (gated under the xchacha20 feature) 192-bit extended nonce variant

⚠️ 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::{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]);

Re-exports

pub use cipher;

Structs

ChaCha	ChaCha family stream cipher, generic around a number of rounds.
ChaCha8Rng	rng Random number generator over the ChaCha8 stream cipher.
ChaCha8RngCore	rng Core random number generator, for use with rand_core::block::BlockRng
ChaCha12Rng	rng Random number generator over the ChaCha12 stream cipher.
ChaCha12RngCore	rng Core random number generator, for use with rand_core::block::BlockRng
ChaCha20Legacy	legacy The ChaCha20 stream cipher (legacy "djb" construction with 64-bit nonce).
ChaCha20Rng	rng Random number generator over the ChaCha20 stream cipher.
ChaCha20RngCore	rng Core random number generator, for use with rand_core::block::BlockRng
XChaCha20	xchacha20 XChaCha20 is a ChaCha20 variant with an extended 192-bit (24-byte) nonce.

Constants

BLOCK_SIZE	Size of a ChaCha20 block in bytes
KEY_SIZE	Size of a ChaCha20 key in bytes
MAX_BLOCKS	Maximum number of blocks that can be encrypted with ChaCha20 before the counter overflows.

Type Definitions

ChaCha8	ChaCha8 stream cipher (reduced-round variant of ChaCha20 with 8 rounds)
ChaCha12	ChaCha12 stream cipher (reduced-round variant of ChaCha20 with 12 rounds)
ChaCha20	ChaCha20 stream cipher (RFC 8439 version with 96-bit nonce)
Key	ChaCha20 key type (256-bits/32-bytes)
LegacyNonce	legacy Size of the nonce for the legacy ChaCha20 stream cipher
Nonce	Nonce type (96-bits/12-bytes)
XNonce	xchacha20 EXtended ChaCha20 nonce (192-bits/24-bytes)