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//! 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`](https://docs.rs/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 //! - [`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`](https://docs.rs/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: //! //! <img src="https://raw.githubusercontent.com/RustCrypto/meta/master/img/stream-ciphers/chacha20.png" width="300px"> //! //! 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]); //! ``` //! //! [RFC 8439]: https://tools.ietf.org/html/rfc8439 //! [Salsa20]: https://docs.rs/salsa20 //! [Hazmat!]: https://github.com/RustCrypto/meta/blob/master/HAZMAT.md #![no_std] #![doc( html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg", html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg" )] #![cfg_attr(docsrs, feature(doc_cfg))] #![warn(missing_docs, rust_2018_idioms, trivial_casts, unused_qualifications)] mod backend; #[cfg(feature = "cipher")] mod chacha; #[cfg(feature = "legacy")] mod legacy; mod max_blocks; #[cfg(feature = "rng")] mod rng; mod rounds; #[cfg(feature = "xchacha")] mod xchacha; #[cfg(feature = "cipher")] pub use cipher; #[cfg(feature = "cipher")] pub use crate::chacha::{ChaCha, ChaCha12, ChaCha20, ChaCha8, Key, Nonce}; #[cfg(feature = "expose-core")] pub use crate::{ backend::Core, rounds::{R12, R20, R8}, }; #[cfg(feature = "hchacha")] pub use crate::xchacha::hchacha; #[cfg(feature = "legacy")] pub use crate::legacy::{ChaCha20Legacy, LegacyNonce}; #[cfg(feature = "rng")] pub use rng::{ ChaCha12Rng, ChaCha12RngCore, ChaCha20Rng, ChaCha20RngCore, ChaCha8Rng, ChaCha8RngCore, }; #[cfg(feature = "xchacha")] pub use self::xchacha::{XChaCha12, XChaCha20, XChaCha8, XNonce}; /// Size of a ChaCha20 block in bytes pub const BLOCK_SIZE: usize = 64; /// Size of a ChaCha20 key in bytes pub const KEY_SIZE: usize = 32; /// Number of bytes in the core (non-extended) ChaCha20 IV const IV_SIZE: usize = 8; /// State initialization constant ("expand 32-byte k") const CONSTANTS: [u32; 4] = [0x6170_7865, 0x3320_646e, 0x7962_2d32, 0x6b20_6574];