Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

remove unnecessary Result-wrapping in crypto.rs #474

Closed
wants to merge 1 commit into from
Closed

remove unnecessary Result-wrapping in crypto.rs #474

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
328 changes: 208 additions & 120 deletions rust/protocol/src/crypto.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,156 +1,244 @@
//
// Copyright 2020 Signal Messenger, LLC.
// Copyright 2020-2022 Signal Messenger, LLC.
// SPDX-License-Identifier: AGPL-3.0-only
//

use std::convert::TryInto;
use std::result::Result;
//! Internal convenience wrappers for symmetric cryptographic primitives.

use aes::cipher::{NewCipher, StreamCipher};
use aes::{Aes256, Aes256Ctr};
use arrayref::array_ref;
use block_modes::block_padding::Pkcs7;
use block_modes::{BlockMode, Cbc};
use displaydoc::Display;
use hmac::{Hmac, Mac, NewMac};
use sha2::Sha256;
use subtle::ConstantTimeEq;
use thiserror::Error;

#[derive(Debug)]
pub(crate) enum EncryptionError {
/// The key or IV is the wrong length.
BadKeyOrIv,
}
/// bad ciphertext: {0}
///
/// Either the input is malformed, or the MAC doesn't match on decryption.
///
/// These cases should not be distinguished; message corruption can cause either problem.
#[derive(Debug, Display, Error)]
#[ignore_extra_doc_attributes]
pub struct DecryptionError(pub &'static str);
Comment on lines +19 to +26
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Nitpick: For some reason displaydoc on structs weirds me out; maybe it's because enum cases often get abbreviated docs anyway in a way that types don't. Mind switching to thiserror-style for the Display representation instead?


#[derive(Debug)]
pub(crate) enum DecryptionError {
/// The key or IV is the wrong length.
BadKeyOrIv,
/// Either the input is malformed, or the MAC doesn't match on decryption.
///
/// These cases should not be distinguished; message corruption can cause either problem.
BadCiphertext(&'static str),
}
// TODO: Could be nice to have a type-safe library for manipulating units of bytes safely.
const BITS_PER_BYTE: usize = std::mem::size_of::<u8>() * 8;
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Rust guarantees that size_of::<u8>() is 1, so I think it's fine to just write 8 here. (The named constant still makes sense though.)


fn aes_256_ctr_encrypt(ptext: &[u8], key: &[u8]) -> Result<Vec<u8>, EncryptionError> {
let key: [u8; 32] = key.try_into().map_err(|_| EncryptionError::BadKeyOrIv)?;
/// The length of the key we use for AES encryption in this crate.
pub const AES_256_KEY_SIZE: usize = 256 / BITS_PER_BYTE;

let zero_nonce = [0u8; 16];
let mut cipher = Aes256Ctr::new(key[..].into(), zero_nonce[..].into());
/// The size of the generated nonce we use for AES encryption in this crate.
pub const AES_NONCE_SIZE: usize = 128 / BITS_PER_BYTE;

let mut ctext = ptext.to_vec();
cipher.apply_keystream(&mut ctext);
Ok(ctext)
}
/// Use AES-256 in CTR mode.
pub mod ctr {
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I don't know if I really see the point of this. Yes, there's a little more organization, but "CTR" and "CBR" don't imply "AES-256" by themselves, and they're all just convenience wrappers for the session implementation in any case.

use super::*;

fn aes_256_ctr_decrypt(ctext: &[u8], key: &[u8]) -> Result<Vec<u8>, DecryptionError> {
aes_256_ctr_encrypt(ctext, key).map_err(|e| match e {
EncryptionError::BadKeyOrIv => DecryptionError::BadKeyOrIv,
})
}
pub fn aes_256_ctr_encrypt(ptext: &[u8], key: &[u8; AES_256_KEY_SIZE]) -> Vec<u8> {
let zero_nonce = [0u8; AES_NONCE_SIZE];
let mut cipher = Aes256Ctr::new(key[..].into(), zero_nonce[..].into());

pub(crate) fn aes_256_cbc_encrypt(
ptext: &[u8],
key: &[u8],
iv: &[u8],
) -> Result<Vec<u8>, EncryptionError> {
match Cbc::<Aes256, Pkcs7>::new_from_slices(key, iv) {
Ok(mode) => Ok(mode.encrypt_vec(ptext)),
Err(block_modes::InvalidKeyIvLength) => Err(EncryptionError::BadKeyOrIv),
let mut ctext = ptext.to_vec();
cipher.apply_keystream(&mut ctext);
ctext
}
}

pub(crate) fn aes_256_cbc_decrypt(
ctext: &[u8],
key: &[u8],
iv: &[u8],
) -> Result<Vec<u8>, DecryptionError> {
if ctext.is_empty() || ctext.len() % 16 != 0 {
return Err(DecryptionError::BadCiphertext(
"ciphertext length must be a non-zero multiple of 16",
));
pub fn aes_256_ctr_decrypt(ctext: &[u8], key: &[u8; AES_256_KEY_SIZE]) -> Vec<u8> {
aes_256_ctr_encrypt(ctext, key)
}

let mode =
Cbc::<Aes256, Pkcs7>::new_from_slices(key, iv).map_err(|_| DecryptionError::BadKeyOrIv)?;
mode.decrypt_vec(ctext)
.map_err(|_| DecryptionError::BadCiphertext("failed to decrypt"))
}
/// Length in bytes of the [`Hmac`] key used for [`aes_256_ctr_hmac_encrypt`] and
/// [`aes_256_ctr_hmac_decrypt`].
pub const MAC_KEY_LENGTH: usize = 80 / BITS_PER_BYTE;
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The MAC key isn't 80 bits; only the MAC itself is. The key can in theory be any length and in practice we use a 32-byte key.


pub(crate) fn hmac_sha256(key: &[u8], input: &[u8]) -> [u8; 32] {
let mut hmac =
Hmac::<Sha256>::new_from_slice(key).expect("HMAC-SHA256 should accept any size key");
hmac.update(input);
hmac.finalize().into_bytes().into()
}

pub(crate) fn aes256_ctr_hmacsha256_encrypt(
msg: &[u8],
cipher_key: &[u8],
mac_key: &[u8],
) -> Result<Vec<u8>, EncryptionError> {
let mut ctext = aes_256_ctr_encrypt(msg, cipher_key)?;
let mac = hmac_sha256(mac_key, &ctext);
ctext.extend_from_slice(&mac[..10]);
Ok(ctext)
}
/// Encrypt plaintext `msg` with AES-256 and embed a computed HMAC into the returned bytes.
///
/// *Implementation note: within the body of this method, only the first [`MAC_KEY_LENGTH`]
/// bytes of the computed MAC are used.*
pub fn aes_256_ctr_hmac_encrypt(
msg: &[u8],
cipher_key: &[u8; AES_256_KEY_SIZE],
mac_key: &[u8; MAC_KEY_LENGTH],
) -> Vec<u8> {
let mut ctext = aes_256_ctr_encrypt(msg, cipher_key);
let mac = hmac_sha256(mac_key, &ctext);
ctext.extend_from_slice(&mac[..MAC_KEY_LENGTH]);
ctext
}

pub(crate) fn aes256_ctr_hmacsha256_decrypt(
ctext: &[u8],
cipher_key: &[u8],
mac_key: &[u8],
) -> Result<Vec<u8>, DecryptionError> {
if ctext.len() < 10 {
return Err(DecryptionError::BadCiphertext("truncated ciphertext"));
/// Validate the HMAC `mac_key` against the ciphertext `ctext`, then decrypt `ctext` using
/// AES-256 with `cipher_key` and [`aes_256_ctr_decrypt`].
///
/// *Implementation note: the last [`MAC_KEY_LENGTH`] bytes of the `ctext` slice represent the
/// truncated HMAC of the rest of the message, as generated by [`aes_256_ctr_hmac_encrypt`].*
pub fn aes_256_ctr_hmac_decrypt(
ctext: &[u8],
cipher_key: &[u8; AES_256_KEY_SIZE],
mac_key: &[u8; MAC_KEY_LENGTH],
) -> Result<Vec<u8>, DecryptionError> {
if ctext.len() < MAC_KEY_LENGTH {
return Err(DecryptionError("truncated ciphertext"));
}
let (ctext, ctext_mac) = ctext.split_at(ctext.len() - MAC_KEY_LENGTH);
let ctext_mac = array_ref![ctext_mac, 0, MAC_KEY_LENGTH];
let our_mac = hmac_sha256(mac_key, ctext);
let our_mac = array_ref![&our_mac, 0, MAC_KEY_LENGTH];
let same: bool = our_mac.ct_eq(ctext_mac).into();
if !same {
return Err(DecryptionError("MAC verification failed"));
}
Ok(aes_256_ctr_decrypt(ctext, cipher_key))
}
let ptext_len = ctext.len() - 10;
let our_mac = hmac_sha256(mac_key, &ctext[..ptext_len]);
let same: bool = our_mac[..10].ct_eq(&ctext[ptext_len..]).into();
if !same {
return Err(DecryptionError::BadCiphertext("MAC verification failed"));

#[cfg(test)]
mod test {
use super::*;

use std::convert::TryInto;

use rand::rngs::OsRng;
use rand::Rng;

#[test]
fn static_test() {
let key: [u8; AES_256_KEY_SIZE] =
hex::decode("603DEB1015CA71BE2B73AEF0857D77811F352C073B6108D72D9810A30914DFF4")
.expect("valid hex")
.try_into()
.expect("correct array size");
Comment on lines +108 to +112
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The hex_literal crate used elsewhere in the workspace can check these conditions at compile time; if you're adding more tests it might be a good time to switch over (incrementally).

let ptext = [0u8; 35];

let ctext = aes_256_ctr_encrypt(&ptext, &key);
assert_eq!(
hex::encode(ctext),
"e568f68194cf76d6174d4cc04310a85491151e5d0b7a1f1bc0d7acd0ae3e51e4170e23"
);
}

#[test]
fn no_hmac_test() {
let key: [u8; AES_256_KEY_SIZE] = (&mut OsRng).gen();
let ptext: [u8; 30] = (&mut OsRng).gen();

let ctext = aes_256_ctr_encrypt(&ptext, &key);
let decrypted = aes_256_ctr_decrypt(&ctext, &key);
assert_eq!(ptext.as_ref(), &decrypted);
}

#[test]
fn hmac_test() {
let key: [u8; AES_256_KEY_SIZE] = (&mut OsRng).gen();
let mac_key: [u8; MAC_KEY_LENGTH] = (&mut OsRng).gen();
let ptext: [u8; 30] = (&mut OsRng).gen();

let ctext = aes_256_ctr_hmac_encrypt(&ptext, &key, &mac_key);
let decrypted =
aes_256_ctr_hmac_decrypt(&ctext, &key, &mac_key).expect("valid decryption");
assert_eq!(ptext.as_ref(), &decrypted);
}
}
aes_256_ctr_decrypt(&ctext[..ptext_len], cipher_key)
}

#[cfg(test)]
mod test {
/// Use AES-256 in CBC mode.
pub mod cbc {
use super::*;

#[test]
fn aes_cbc_test() {
let key = hex::decode("4e22eb16d964779994222e82192ce9f747da72dc4abe49dfdeeb71d0ffe3796e")
.expect("valid hex");
let iv = hex::decode("6f8a557ddc0a140c878063a6d5f31d3d").expect("valid hex");

let ptext = hex::decode("30736294a124482a4159").expect("valid hex");

let ctext = aes_256_cbc_encrypt(&ptext, &key, &iv).expect("valid key and IV");
assert_eq!(
hex::encode(ctext.clone()),
"dd3f573ab4508b9ed0e45e0baf5608f3"
);

let recovered = aes_256_cbc_decrypt(&ctext, &key, &iv).expect("valid");
assert_eq!(hex::encode(ptext), hex::encode(recovered.clone()));

// padding is invalid:
assert!(aes_256_cbc_decrypt(&recovered, &key, &iv).is_err());
assert!(aes_256_cbc_decrypt(&ctext, &key, &ctext).is_err());
pub fn aes_256_cbc_encrypt(
ptext: &[u8],
key: &[u8; AES_256_KEY_SIZE],
iv: &[u8; AES_NONCE_SIZE],
) -> Vec<u8> {
let mode =
Cbc::<Aes256, Pkcs7>::new_from_slices(key, iv).expect("key and iv were fixed length");
mode.encrypt_vec(ptext)
}

// bitflip the IV to cause a change in the recovered text
let bad_iv = hex::decode("ef8a557ddc0a140c878063a6d5f31d3d").expect("valid hex");
let recovered = aes_256_cbc_decrypt(&ctext, &key, &bad_iv).expect("still valid");
assert_eq!(hex::encode(recovered), "b0736294a124482a4159");
pub fn aes_256_cbc_decrypt(
ctext: &[u8],
key: &[u8; AES_256_KEY_SIZE],
iv: &[u8; AES_NONCE_SIZE],
) -> Result<Vec<u8>, DecryptionError> {
if ctext.is_empty() || ctext.len() % 16 != 0 {
return Err(DecryptionError(
"ciphertext length must be a non-zero multiple of 16",
));
}

let mode = Cbc::<Aes256, Pkcs7>::new_from_slices(key.as_ref(), iv.as_ref())
.expect("key and iv were fixed length");
mode.decrypt_vec(ctext)
.map_err(|_| DecryptionError("failed to decrypt"))
}

#[test]
fn aes_ctr_test() {
let key = hex::decode("603DEB1015CA71BE2B73AEF0857D77811F352C073B6108D72D9810A30914DFF4")
.expect("valid hex");
let ptext = [0u8; 35];

let ctext = aes_256_ctr_encrypt(&ptext, &key).expect("valid key");
assert_eq!(
hex::encode(ctext),
"e568f68194cf76d6174d4cc04310a85491151e5d0b7a1f1bc0d7acd0ae3e51e4170e23"
);
#[cfg(test)]
mod test {
use super::*;

use std::convert::TryInto;

use rand::rngs::OsRng;
use rand::Rng;

#[test]
fn static_test() {
let key: [u8; AES_256_KEY_SIZE] =
hex::decode("4e22eb16d964779994222e82192ce9f747da72dc4abe49dfdeeb71d0ffe3796e")
.expect("valid hex")
.try_into()
.expect("correct array size");
let iv: [u8; AES_NONCE_SIZE] = hex::decode("6f8a557ddc0a140c878063a6d5f31d3d")
.expect("valid hex")
.try_into()
.expect("correct array size");

let ptext = hex::decode("30736294a124482a4159").expect("valid hex");

let ctext = cbc::aes_256_cbc_encrypt(&ptext, &key, &iv);
assert_eq!(
hex::encode(ctext.clone()),
"dd3f573ab4508b9ed0e45e0baf5608f3"
);

let recovered = cbc::aes_256_cbc_decrypt(&ctext, &key, &iv).expect("valid");
assert_eq!(hex::encode(ptext), hex::encode(recovered.clone()));

// padding is invalid:
assert!(cbc::aes_256_cbc_decrypt(&recovered, &key, &iv).is_err());
assert!(
cbc::aes_256_cbc_decrypt(&ctext, &key, array_ref![&ctext, 0, AES_NONCE_SIZE])
.is_err()
);

// bitflip the IV to cause a change in the recovered text
let bad_iv: [u8; AES_NONCE_SIZE] = hex::decode("ef8a557ddc0a140c878063a6d5f31d3d")
.expect("valid hex")
.try_into()
.expect("correct array size");
let recovered = cbc::aes_256_cbc_decrypt(&ctext, &key, &bad_iv).expect("still valid");
assert_eq!(hex::encode(recovered), "b0736294a124482a4159");
}

#[test]
fn random_test() {
let key: [u8; AES_256_KEY_SIZE] = (&mut OsRng).gen();
let iv: [u8; AES_NONCE_SIZE] = (&mut OsRng).gen();
let ptext: [u8; 30] = (&mut OsRng).gen();

let ctext = aes_256_cbc_encrypt(&ptext, &key, &iv);
let decrypted = aes_256_cbc_decrypt(&ctext, &key, &iv).expect("valid decryption");
assert_eq!(ptext.as_ref(), &decrypted);
}
}
}

/// Calculate the [`Hmac`]-[`Sha256`] code over `input` using `key`.
pub fn hmac_sha256(key: &[u8], input: &[u8]) -> [u8; 256 / BITS_PER_BYTE] {
let mut hmac =
Hmac::<Sha256>::new_from_slice(key).expect("HMAC-SHA256 should accept any size key");
hmac.update(input);
hmac.finalize().into_bytes().into()
}
Loading