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#![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"
)]
#![forbid(unsafe_code)]
#![warn(missing_docs, rust_2018_idioms)]
pub use cipher;
use cipher::{
errors::LoopError,
generic_array::{typenum::Unsigned, GenericArray},
Block, BlockCipher, BlockEncrypt, FromBlockCipher, StreamCipher,
};
pub struct Ofb<C: BlockCipher> {
cipher: C,
block: Block<C>,
pos: usize,
}
impl<C> FromBlockCipher for Ofb<C>
where
C: BlockCipher + BlockEncrypt,
{
type BlockCipher = C;
type NonceSize = C::BlockSize;
fn from_block_cipher(cipher: C, iv: &GenericArray<u8, Self::NonceSize>) -> Self {
let mut block = iv.clone();
cipher.encrypt_block(&mut block);
Self {
cipher,
block,
pos: 0,
}
}
}
impl<C: BlockCipher + BlockEncrypt> StreamCipher for Ofb<C> {
fn try_apply_keystream(&mut self, mut data: &mut [u8]) -> Result<(), LoopError> {
let bs = C::BlockSize::to_usize();
let n = data.len();
if n < bs - self.pos {
xor(data, &self.block[self.pos..self.pos + n]);
self.pos += n;
return Ok(());
}
let (left, right) = { data }.split_at_mut(bs - self.pos);
data = right;
let mut block = self.block.clone();
xor(left, &block[self.pos..]);
self.cipher.encrypt_block(&mut block);
let mut chunks = data.chunks_exact_mut(bs);
for chunk in &mut chunks {
xor(chunk, &block);
self.cipher.encrypt_block(&mut block);
}
let rem = chunks.into_remainder();
xor(rem, &block[..rem.len()]);
self.block = block;
self.pos = rem.len();
Ok(())
}
}
#[inline(always)]
fn xor(buf1: &mut [u8], buf2: &[u8]) {
debug_assert_eq!(buf1.len(), buf2.len());
for (a, b) in buf1.iter_mut().zip(buf2) {
*a ^= *b;
}
}