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use crate::traits::BlockMode;
use crate::utils::{xor, Block, ParBlocks};
use block_cipher::generic_array::typenum::Unsigned;
use block_cipher::generic_array::GenericArray;
use block_cipher::{BlockCipher, NewBlockCipher};
use block_padding::Padding;
use core::marker::PhantomData;
use core::ptr;
pub struct Cfb<C: BlockCipher + BlockCipher, P: Padding> {
cipher: C,
iv: GenericArray<u8, C::BlockSize>,
_p: PhantomData<P>,
}
impl<C, P> BlockMode<C, P> for Cfb<C, P>
where
C: BlockCipher + NewBlockCipher,
P: Padding,
{
type IvSize = C::BlockSize;
fn new(cipher: C, iv: &Block<C>) -> Self {
let mut iv = iv.clone();
cipher.encrypt_block(&mut iv);
Self {
cipher,
iv,
_p: Default::default(),
}
}
fn encrypt_blocks(&mut self, blocks: &mut [Block<C>]) {
for block in blocks {
xor_set1(block, self.iv.as_mut_slice());
self.cipher.encrypt_block(&mut self.iv);
}
}
fn decrypt_blocks(&mut self, mut blocks: &mut [Block<C>]) {
let pb = C::ParBlocks::to_usize();
if blocks.len() >= pb {
#[allow(unsafe_code)]
let mut par_iv = read_par_block::<C>(blocks);
self.cipher.encrypt_blocks(&mut par_iv);
let (b, r) = { blocks }.split_at_mut(1);
blocks = r;
xor(&mut b[0], &self.iv);
while blocks.len() >= 2 * pb - 1 {
let next_par_iv = read_par_block::<C>(&blocks[pb - 1..]);
let (par_block, r) = { blocks }.split_at_mut(pb);
blocks = r;
for (a, b) in par_block.iter_mut().zip(par_iv.iter()) {
xor(a, b)
}
par_iv = next_par_iv;
self.cipher.encrypt_blocks(&mut par_iv);
}
let (par_block, r) = { blocks }.split_at_mut(pb - 1);
blocks = r;
for (a, b) in par_block.iter_mut().zip(par_iv[..pb - 1].iter()) {
xor(a, b)
}
self.iv = par_iv[pb - 1].clone();
}
for block in blocks {
xor_set2(block, self.iv.as_mut_slice());
self.cipher.encrypt_block(&mut self.iv);
}
}
}
#[inline(always)]
fn read_par_block<C: BlockCipher>(blocks: &[Block<C>]) -> ParBlocks<C> {
assert!(blocks.len() >= C::ParBlocks::to_usize());
#[allow(unsafe_code)]
unsafe {
ptr::read(blocks.as_ptr() as *const ParBlocks<C>)
}
}
#[inline(always)]
fn xor_set1(buf1: &mut [u8], buf2: &mut [u8]) {
for (a, b) in buf1.iter_mut().zip(buf2) {
let t = *a ^ *b;
*a = t;
*b = t;
}
}
#[inline(always)]
fn xor_set2(buf1: &mut [u8], buf2: &mut [u8]) {
for (a, b) in buf1.iter_mut().zip(buf2) {
let t = *a;
*a ^= *b;
*b = t;
}
}