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//! Ciphers used to implement the Tor protocols.
//!
//! Fortunately, Tor has managed not to proliferate ciphers. It only
//! uses AES, and (so far) only uses AES in counter mode.
/// Re-exports implementations of counter-mode AES.
///
/// These ciphers implement the `cipher::StreamCipher` trait, so use
/// the [`cipher`](https://docs.rs/cipher) crate to access them.
#[cfg_attr(docsrs, doc(cfg(true)))]
#[cfg(not(feature = "with-openssl"))]
pub mod aes {
// These implement StreamCipher.
/// AES128 in counter mode as used by Tor.
pub type Aes128Ctr = ctr::Ctr128BE<aes::Aes128>;
/// AES256 in counter mode as used by Tor.
pub type Aes256Ctr = ctr::Ctr128BE<aes::Aes256>;
}
/// Compatibility layer between OpenSSL and `cipher::StreamCipher`.
#[cfg(feature = "with-openssl")]
use cipher::common::array::Array;
use cipher::common::{InnerUser, KeyInit, KeySizeUser};
use cipher::inout::InOutBuf;
use cipher::{InnerIvInit, IvSizeUser, StreamCipher, StreamCipherError};
use openssl::symm::{Cipher, Crypter, Mode};
use zeroize::{Zeroize, ZeroizeOnDrop};
/// AES 128 in counter mode as used by Tor.
pub struct Aes128Ctr(
/// Underlying openssl crypto context.
Crypter,
);
/// AES 128 key
#[derive(Zeroize, ZeroizeOnDrop)]
pub struct Aes128Key([u8; 16]);
impl KeySizeUser for Aes128Key {
type KeySize = typenum::consts::U16;
impl KeyInit for Aes128Key {
fn new(key: &Array<u8, Self::KeySize>) -> Self {
Aes128Key((*key).into())
impl InnerUser for Aes128Ctr {
type Inner = Aes128Key;
impl IvSizeUser for Aes128Ctr {
type IvSize = typenum::consts::U16;
impl StreamCipher for Aes128Ctr {
fn check_remaining(&self, _data_len: usize) -> Result<(), StreamCipherError> {
// NOTE: this is not a sefe pattern in general, but since the underlying counter
// is 128 bits, we don't need to worry about overflowing it.
Ok(())
fn unchecked_apply_keystream_inout(&mut self, mut buf: InOutBuf<'_, '_, u8>) {
// TODO(nickm): It would be lovely if we could get rid of this copy somehow.
let in_buf = zeroize::Zeroizing::new(buf.get_in().to_vec());
self.0
.update(&in_buf, buf.get_out())
.expect("OpenSSL AES encryption failed.");
fn unchecked_write_keystream(&mut self, buf: &mut [u8]) {
// TODO(nickm): It would be lovely if we could get rid of this vec somehow.
let z = vec![0; buf.len()];
.update(&z, buf)
impl InnerIvInit for Aes128Ctr {
fn inner_iv_init(inner: Self::Inner, iv: &Array<u8, Self::IvSize>) -> Self {
let crypter = Crypter::new(Cipher::aes_128_ctr(), Mode::Encrypt, &inner.0, Some(iv))
.expect("openssl error while initializing Aes128Ctr");
Aes128Ctr(crypter)
/// AES 256 in counter mode as used by Tor.
pub struct Aes256Ctr(Crypter);
/// AES 256 key
pub struct Aes256Key([u8; 32]);
impl KeySizeUser for Aes256Key {
type KeySize = typenum::consts::U32;
impl KeyInit for Aes256Key {
Aes256Key((*key).into())
impl InnerUser for Aes256Ctr {
type Inner = Aes256Key;
impl IvSizeUser for Aes256Ctr {
impl StreamCipher for Aes256Ctr {
impl InnerIvInit for Aes256Ctr {
let crypter = Crypter::new(Cipher::aes_256_ctr(), Mode::Encrypt, &inner.0, Some(iv))
.expect("openssl error while initializing Aes256Ctr");
Aes256Ctr(crypter)