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// Copyright 2023 The rust-ggstd authors. All rights reserved.
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//! Cipher block chaining (CBC) mode.
//!
//! CBC provides confidentiality by xoring (chaining) each plaintext block
//! with the previous ciphertext block before applying the block cipher.
//!
//! See NIST SP 800-38A, pp 10-11
use crate::compat;
use crate::crypto::cipher::{Block, BlockMode};
use crate::crypto::subtle;
/// CBCEncrypter implements encryption in cipher block chaining
/// mode, using the given Block.
pub struct CBCEncrypter<'a, B: Block> {
b: &'a B,
block_size: usize,
iv: Vec<u8>,
tmp: Vec<u8>,
}
impl<'a, B: Block> CBCEncrypter<'a, B> {
/// new returns a BlockMode which encrypts in cipher block chaining
/// mode, using the given Block. The length of iv must be the same as the
/// Block's block size.
pub fn new(b: &'a B, iv: &[u8]) -> Self {
let blocksize = b.block_size();
if iv.len() != blocksize {
panic!("cipher.NewCBCEncrypter: IV length must equal block size");
}
Self {
b,
block_size: blocksize,
iv: iv.to_vec(),
tmp: vec![0; blocksize],
}
}
pub fn set_iv(&mut self, iv: &[u8]) {
if iv.len() != self.iv.len() {
panic!("cipher: incorrect length IV");
}
compat::copy(&mut self.iv, iv);
}
}
impl<'a, B: Block> BlockMode for CBCEncrypter<'a, B> {
fn block_size(&self) -> usize {
self.block_size
}
fn crypt_blocks(&mut self, dst: &mut [u8], src: &[u8]) {
let block_size = self.block_size;
if src.len() % block_size != 0 {
panic!("crypto/cipher: input not full blocks");
}
if dst.len() < src.len() {
panic!("crypto/cipher: output smaller than input");
}
if src.is_empty() {
return;
}
let tmp = &mut self.tmp;
// The first block is special because it uses the saved iv.
subtle::xor_bytes(tmp, &src[..block_size], &self.iv);
self.b.encrypt(&mut dst[..block_size], tmp);
// The rest is encrypted using the previous block as IV
let mut offset = block_size;
let mut iv_offset = 0;
while offset < src.len() {
subtle::xor_bytes(
tmp,
&src[offset..offset + block_size],
&dst[iv_offset..iv_offset + block_size],
);
self.b.encrypt(&mut dst[offset..offset + block_size], tmp);
offset += block_size;
iv_offset += block_size;
}
// save the last encrypted block as the IV for the next encryption
compat::copy(&mut self.iv, &dst[iv_offset..iv_offset + block_size]);
}
fn crypt_blocks_inplace(&mut self, data: &mut [u8]) {
let block_size = self.block_size;
if data.len() % block_size != 0 {
panic!("crypto/cipher: input not full blocks");
}
if data.is_empty() {
return;
}
let tmp = &mut self.tmp;
// The first block is special because it uses the saved iv.
subtle::xor_bytes(tmp, &data[..block_size], &self.iv);
self.b.encrypt(&mut data[..block_size], tmp);
// The rest is encrypted using the previous block as IV
let mut prev = 0;
let mut start = block_size;
let mut end = start + block_size;
while start < data.len() {
subtle::xor_bytes(tmp, &data[start..end], &data[prev..start]);
self.b.encrypt(&mut data[start..end], tmp);
(prev, start, end) = (start, end, end + block_size);
}
// save the last encrypted block as the IV for the next encryption
compat::copy(&mut self.iv, &data[data.len() - block_size..]);
}
}
/// CBCDecrypter implements decryption in cipher block chaining
/// mode, using the given Block.
pub struct CBCDecrypter<'a, B: Block> {
b: &'a B,
block_size: usize,
iv: Vec<u8>,
tmp: Vec<u8>,
tmp_next_iv: Vec<u8>,
}
impl<'a, B: Block> CBCDecrypter<'a, B> {
/// new returns a BlockMode which decrypts in cipher block chaining
/// mode, using the given Block. The length of iv must be the same as the
/// Block's block size and must match the iv used to encrypt the data.
pub fn new(b: &'a B, iv: &[u8]) -> Self {
let blocksize = b.block_size();
if iv.len() != blocksize {
panic!("cipher.NewCBCDecrypter: IV length must equal block size");
}
Self {
b,
block_size: blocksize,
iv: iv.to_vec(),
tmp: vec![0; blocksize],
tmp_next_iv: vec![0; blocksize],
}
}
pub fn set_iv(&mut self, iv: &[u8]) {
if iv.len() != self.iv.len() {
panic!("cipher: incorrect length IV");
}
compat::copy(&mut self.iv, iv);
}
}
impl<'a, B: Block> BlockMode for CBCDecrypter<'a, B> {
fn block_size(&self) -> usize {
self.block_size
}
fn crypt_blocks(&mut self, dst: &mut [u8], src: &[u8]) {
let block_size = self.block_size;
if src.len() % block_size != 0 {
panic!("crypto/cipher: input not full blocks");
}
if dst.len() < src.len() {
panic!("crypto/cipher: output smaller than input");
}
if src.is_empty() {
return;
}
let tmp = &mut self.tmp;
// For each block, we need to xor the decrypted data with the previous block's ciphertext (the iv).
// The first block is special because it uses the saved iv.
self.b.decrypt(tmp, &src[..block_size]);
subtle::xor_bytes(&mut dst[..block_size], tmp, &self.iv);
// The rest is encrypted using the previous block as IV
let mut prev = 0;
let mut start = block_size;
let mut end = start + block_size;
while start < src.len() {
self.b.decrypt(tmp, &src[start..end]);
subtle::xor_bytes(&mut dst[start..end], tmp, &src[prev..start]);
(prev, start, end) = (start, end, end + block_size);
}
// save the last source block as the IV for the next decryption
compat::copy(&mut self.iv, &src[src.len() - block_size..]);
}
fn crypt_blocks_inplace(&mut self, data: &mut [u8]) {
let block_size = self.block_size;
if data.len() % block_size != 0 {
panic!("crypto/cipher: input not full blocks");
}
if data.is_empty() {
return;
}
let tmp = &mut self.tmp;
// For each block, we need to xor the decrypted data with the previous block's ciphertext (the iv).
// To avoid making a copy each time, we loop over the blocks BACKWARDS.
let mut end = data.len();
let mut start = end - block_size;
let mut prev = start - block_size;
// Copy the last block of ciphertext in preparation as the new iv.
compat::copy(&mut self.tmp_next_iv, &data[start..end]);
// Loop over all but the first block.
while start > 0 {
self.b.decrypt(tmp, &data[start..end]);
// we need:
// - data[start..end] as writable
// - data[prev..start] as readable
subtle::xor_bytes(
unsafe { std::slice::from_raw_parts_mut(data.as_mut_ptr().add(start), block_size) },
unsafe { std::slice::from_raw_parts(data.as_ptr().add(prev), block_size) },
tmp,
);
(end, start, prev) = (start, prev, prev.wrapping_sub(block_size));
}
// The first block is special because it uses the saved iv.
self.b.decrypt(tmp, &data[..block_size]);
subtle::xor_bytes(&mut data[..block_size], tmp, &self.iv);
// Set the new iv to the first block we copied earlier.
compat::copy(&mut self.iv, &self.tmp_next_iv);
}
}