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use aes::cipher::generic_array::GenericArray;
use aes::cipher::BlockEncrypt;
use std::io::{Read, Result as IoResult};
#[allow(dead_code)]
pub struct AesDecoder<Io: Read, Aes: BlockEncrypt> {
io: Io,
aes: Aes,
counter: u128,
block: [u8; 16],
lower: usize,
upper: usize,
}
impl<Io: Read, Aes: BlockEncrypt> AesDecoder<Io, Aes> {
pub fn new(io: Io, aes: Aes) -> IoResult<Self> {
let mut decoder = Self {
io,
aes,
counter: 0,
block: [0; 16],
lower: 0,
upper: 0,
};
decoder.update_block()?;
Ok(decoder)
}
#[inline]
fn update_block(&mut self) -> IoResult<()> {
self.upper = self.io.read(&mut self.block)?;
self.lower = 0;
self.counter += 1;
let mut mask = self.counter.to_le_bytes();
self.aes
.encrypt_block(GenericArray::from_mut_slice(&mut mask));
for (b, m) in self.block.iter_mut().zip(mask) {
*b ^= m
}
Ok(())
}
}
impl<Io: Read, Aes: BlockEncrypt> Read for AesDecoder<Io, Aes> {
fn read(&mut self, mut buf: &mut [u8]) -> IoResult<usize> {
let mut bytes = 0;
while !buf.is_empty() && self.lower != self.upper {
for (to, fr) in buf.iter_mut().zip(&self.block[self.lower..self.upper]) {
*to = *fr
}
let consumed = buf.len().min(self.upper - self.lower);
buf = &mut buf[consumed..];
self.lower += consumed;
bytes += consumed;
if self.lower == 16 {
self.update_block()?;
}
}
Ok(bytes)
}
}
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