cts/
cbc_cs3.rs

1use crate::{Decrypt, Encrypt, Error, cbc_dec, cbc_enc, xor};
2use cipher::{
3    Block, BlockCipherDecBackend, BlockCipherDecClosure, BlockCipherDecrypt, BlockCipherEncBackend,
4    BlockCipherEncClosure, BlockCipherEncrypt, BlockSizeUser, InnerIvInit, IvSizeUser,
5    array::{Array, ArraySize},
6    common::InnerUser,
7    inout::InOutBuf,
8    typenum::Unsigned,
9};
10
11/// The CBC-CS-3 ciphertext stealing mode.
12#[derive(Debug)]
13pub struct CbcCs3<C: BlockSizeUser> {
14    cipher: C,
15    iv: Block<C>,
16}
17
18impl<C: BlockSizeUser> InnerUser for CbcCs3<C> {
19    type Inner = C;
20}
21
22impl<C: BlockSizeUser> IvSizeUser for CbcCs3<C> {
23    type IvSize = C::BlockSize;
24}
25
26impl<C: BlockSizeUser> InnerIvInit for CbcCs3<C> {
27    fn inner_iv_init(cipher: Self::Inner, iv: &cipher::Iv<Self>) -> Self {
28        Self {
29            cipher,
30            iv: iv.clone(),
31        }
32    }
33}
34
35impl<C: BlockCipherEncrypt> Encrypt for CbcCs3<C> {
36    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
37        if buf.len() < C::BlockSize::USIZE {
38            return Err(Error);
39        }
40        let Self { cipher, iv } = self;
41        cipher.encrypt_with_backend(Closure { iv, buf });
42        Ok(())
43    }
44}
45
46impl<C: BlockCipherDecrypt> Decrypt for CbcCs3<C> {
47    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
48        if buf.len() < C::BlockSize::USIZE {
49            return Err(Error);
50        }
51        let Self { cipher, iv } = self;
52        cipher.decrypt_with_backend(Closure { iv, buf });
53        Ok(())
54    }
55}
56
57struct Closure<'a, BS: ArraySize> {
58    iv: Array<u8, BS>,
59    buf: InOutBuf<'a, 'a, u8>,
60}
61
62impl<BS: ArraySize> BlockSizeUser for Closure<'_, BS> {
63    type BlockSize = BS;
64}
65
66impl<BS: ArraySize> BlockCipherEncClosure for Closure<'_, BS> {
67    fn call<B: BlockCipherEncBackend<BlockSize = BS>>(self, cipher: &B) {
68        let Self { mut iv, mut buf } = self;
69        let (mut blocks, mut tail) = buf.reborrow().into_chunks();
70
71        cbc_enc(cipher, &mut iv, blocks.reborrow());
72
73        if tail.is_empty() && blocks.len() > 1 {
74            let blocks = blocks.get_out();
75            let (last, rest) = blocks.split_last_mut().unwrap();
76            let (penultimate, _) = rest.split_last_mut().unwrap();
77            core::mem::swap(penultimate, last);
78        } else {
79            let mut block = Block::<B>::default();
80            block[..tail.len()].copy_from_slice(tail.get_in());
81            xor(&mut block, &iv);
82            cipher.encrypt_block_inplace(&mut block);
83
84            let penult_block = blocks.get_out().last_mut().unwrap();
85            let val = core::mem::replace(penult_block, block);
86
87            let tail_val = &val[..tail.len()];
88            tail.get_out().copy_from_slice(tail_val);
89        }
90    }
91}
92
93impl<BS: ArraySize> BlockCipherDecClosure for Closure<'_, BS> {
94    fn call<B: BlockCipherDecBackend<BlockSize = BS>>(self, cipher: &B) {
95        let Self { mut iv, buf } = self;
96
97        let bs = B::BlockSize::USIZE;
98        let blocks_len = buf.len().div_ceil(bs);
99        let main_blocks = blocks_len.saturating_sub(2);
100
101        let (blocks, mut tail) = buf.split_at(bs * main_blocks);
102        let (blocks, rem) = blocks.into_chunks();
103        debug_assert_eq!(rem.len(), 0);
104
105        cbc_dec(cipher, &mut iv, blocks);
106
107        let n = tail.len() - bs;
108        let mut block1: Block<B> = tail.get_in()[..bs].try_into().unwrap();
109        cipher.decrypt_block_inplace(&mut block1);
110
111        let mut block2 = Block::<B>::default();
112        block2[..n].copy_from_slice(&tail.get_in()[bs..]);
113        block2[n..].copy_from_slice(&block1[n..]);
114        xor(&mut block1, &block2);
115
116        cipher.decrypt_block_inplace(&mut block2);
117        xor(&mut block2, &iv);
118
119        let (l, r) = tail.get_out().split_at_mut(bs);
120        l.copy_from_slice(&block2);
121        r.copy_from_slice(&block1[..n]);
122    }
123}
cts/cbc_cs3.rs

cts/
cbc_cs3.rs
