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use super::{ChaChaCore, Key, Nonce, CONSTANTS, STATE_WORDS};
use cipher::{
consts::{U10, U16, U24, U32, U4, U6, U64},
generic_array::{typenum::Unsigned, GenericArray},
BlockSizeUser, IvSizeUser, KeyIvInit, KeySizeUser, StreamCipherCore, StreamCipherCoreWrapper,
StreamCipherSeekCore, StreamClosure,
};
#[cfg(feature = "zeroize")]
use cipher::zeroize::ZeroizeOnDrop;
pub type XNonce = GenericArray<u8, U24>;
pub type XChaCha20 = StreamCipherCoreWrapper<XChaChaCore<U10>>;
pub type XChaCha12 = StreamCipherCoreWrapper<XChaChaCore<U6>>;
pub type XChaCha8 = StreamCipherCoreWrapper<XChaChaCore<U4>>;
pub struct XChaChaCore<R: Unsigned>(ChaChaCore<R>);
impl<R: Unsigned> KeySizeUser for XChaChaCore<R> {
type KeySize = U32;
}
impl<R: Unsigned> IvSizeUser for XChaChaCore<R> {
type IvSize = U24;
}
impl<R: Unsigned> BlockSizeUser for XChaChaCore<R> {
type BlockSize = U64;
}
impl<R: Unsigned> KeyIvInit for XChaChaCore<R> {
fn new(key: &Key, iv: &XNonce) -> Self {
let subkey = hchacha::<R>(key, iv[..16].as_ref().into());
let mut padded_iv = Nonce::default();
padded_iv[4..].copy_from_slice(&iv[16..]);
XChaChaCore(ChaChaCore::new(&subkey, &padded_iv))
}
}
impl<R: Unsigned> StreamCipherCore for XChaChaCore<R> {
#[inline(always)]
fn remaining_blocks(&self) -> Option<usize> {
self.0.remaining_blocks()
}
#[inline(always)]
fn process_with_backend(&mut self, f: impl StreamClosure<BlockSize = Self::BlockSize>) {
self.0.process_with_backend(f);
}
}
impl<R: Unsigned> StreamCipherSeekCore for XChaChaCore<R> {
type Counter = u32;
#[inline(always)]
fn get_block_pos(&self) -> u32 {
self.0.get_block_pos()
}
#[inline(always)]
fn set_block_pos(&mut self, pos: u32) {
self.0.set_block_pos(pos);
}
}
#[cfg(feature = "zeroize")]
#[cfg_attr(docsrs, doc(cfg(feature = "zeroize")))]
impl<R: Unsigned> ZeroizeOnDrop for XChaChaCore<R> {}
pub fn hchacha<R: Unsigned>(key: &Key, input: &GenericArray<u8, U16>) -> GenericArray<u8, U32> {
let mut state = [0u32; STATE_WORDS];
state[..4].copy_from_slice(&CONSTANTS);
let key_chunks = key.chunks_exact(4);
for (v, chunk) in state[4..12].iter_mut().zip(key_chunks) {
*v = u32::from_le_bytes(chunk.try_into().unwrap());
}
let input_chunks = input.chunks_exact(4);
for (v, chunk) in state[12..16].iter_mut().zip(input_chunks) {
*v = u32::from_le_bytes(chunk.try_into().unwrap());
}
for _ in 0..R::USIZE {
quarter_round(0, 4, 8, 12, &mut state);
quarter_round(1, 5, 9, 13, &mut state);
quarter_round(2, 6, 10, 14, &mut state);
quarter_round(3, 7, 11, 15, &mut state);
quarter_round(0, 5, 10, 15, &mut state);
quarter_round(1, 6, 11, 12, &mut state);
quarter_round(2, 7, 8, 13, &mut state);
quarter_round(3, 4, 9, 14, &mut state);
}
let mut output = GenericArray::default();
for (chunk, val) in output[..16].chunks_exact_mut(4).zip(&state[..4]) {
chunk.copy_from_slice(&val.to_le_bytes());
}
for (chunk, val) in output[16..].chunks_exact_mut(4).zip(&state[12..]) {
chunk.copy_from_slice(&val.to_le_bytes());
}
output
}
fn quarter_round(a: usize, b: usize, c: usize, d: usize, state: &mut [u32; STATE_WORDS]) {
state[a] = state[a].wrapping_add(state[b]);
state[d] ^= state[a];
state[d] = state[d].rotate_left(16);
state[c] = state[c].wrapping_add(state[d]);
state[b] ^= state[c];
state[b] = state[b].rotate_left(12);
state[a] = state[a].wrapping_add(state[b]);
state[d] ^= state[a];
state[d] = state[d].rotate_left(8);
state[c] = state[c].wrapping_add(state[d]);
state[b] ^= state[c];
state[b] = state[b].rotate_left(7);
}
#[cfg(test)]
mod hchacha20_tests {
use super::*;
use hex_literal::hex;
#[test]
fn test_vector() {
const KEY: [u8; 32] = hex!(
"000102030405060708090a0b0c0d0e0f"
"101112131415161718191a1b1c1d1e1f"
);
const INPUT: [u8; 16] = hex!("000000090000004a0000000031415927");
const OUTPUT: [u8; 32] = hex!(
"82413b4227b27bfed30e42508a877d73"
"a0f9e4d58a74a853c12ec41326d3ecdc"
);
let actual = hchacha::<U10>(
GenericArray::from_slice(&KEY),
&GenericArray::from_slice(&INPUT),
);
assert_eq!(actual.as_slice(), &OUTPUT);
}
}