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//! **ChaCha20Poly1305** ([RFC 8439][1]) is an
//! [Authenticated Encryption with Associated Data (AEAD)][2]
//! cipher amenable to fast, constant-time implementations in software, based on
//! the [ChaCha20][3] stream cipher and [Poly1305][4] universal hash function.
//!
//! This crate also contains an implementation of **XSalsa20Poly1305**
//! (a.k.a. NaCl `crypto_secretbox`[4]): a variant of Salsa20Poly1305 with an
//! extended 192-bit (24-byte) nonce.
//!
//! [1]: https://tools.ietf.org/html/rfc8439
//! [2]: https://en.wikipedia.org/wiki/Authenticated_encryption
//! [3]: https://github.com/RustCrypto/stream-ciphers/tree/master/chacha20
//! [4]: https://github.com/RustCrypto/universal-hashes/tree/master/poly1305

#![no_std]

extern crate alloc;

mod cipher;
#[cfg(feature = "xchacha20poly1305")]
mod xchacha20poly1305;

pub use aead;
#[cfg(feature = "xchacha20poly1305")]
pub use xchacha20poly1305::XChaCha20Poly1305;

use self::cipher::Cipher;
use aead::generic_array::{
    typenum::{U0, U12, U16, U32},
    GenericArray,
};
use aead::{Aead, Error, NewAead, Payload};
use alloc::vec::Vec;
use chacha20::{stream_cipher::NewStreamCipher, ChaCha20};
use zeroize::Zeroize;

/// ChaCha20Poly1305 Authenticated Encryption with Additional Data (AEAD)
#[derive(Clone)]
pub struct ChaCha20Poly1305 {
    /// Secret key
    key: GenericArray<u8, U32>,
}

impl NewAead for ChaCha20Poly1305 {
    type KeySize = U32;

    fn new(key: GenericArray<u8, U32>) -> Self {
        ChaCha20Poly1305 { key }
    }
}

impl Aead for ChaCha20Poly1305 {
    type NonceSize = U12;
    type TagSize = U16;
    type CiphertextOverhead = U0;

    fn encrypt<'msg, 'aad>(
        &self,
        nonce: &GenericArray<u8, Self::NonceSize>,
        plaintext: impl Into<Payload<'msg, 'aad>>,
    ) -> Result<Vec<u8>, Error> {
        Cipher::new(ChaCha20::new(&self.key, nonce)).encrypt(plaintext.into())
    }

    fn decrypt<'msg, 'aad>(
        &self,
        nonce: &GenericArray<u8, Self::NonceSize>,
        ciphertext: impl Into<Payload<'msg, 'aad>>,
    ) -> Result<Vec<u8>, Error> {
        Cipher::new(ChaCha20::new(&self.key, nonce)).decrypt(ciphertext.into())
    }
}

impl Drop for ChaCha20Poly1305 {
    fn drop(&mut self) {
        self.key.as_mut_slice().zeroize();
    }
}