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1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * The "hash function" used as the core of the ChaCha stream cipher (RFC7539)
4 *
5 * Copyright (C) 2015 Martin Willi
6 */
7
8#include <linux/kernel.h>
9#include <linux/export.h>
10#include <linux/bitops.h>
11#include <linux/cryptohash.h>
12#include <asm/unaligned.h>
13#include <crypto/chacha.h>
14
15static void chacha_permute(u32 *x, int nrounds)
16{
17 int i;
18
19 /* whitelist the allowed round counts */
20 WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
21
22 for (i = 0; i < nrounds; i += 2) {
23 x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 16);
24 x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 16);
25 x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 16);
26 x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 16);
27
28 x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 12);
29 x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 12);
30 x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 12);
31 x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 12);
32
33 x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 8);
34 x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 8);
35 x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 8);
36 x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 8);
37
38 x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 7);
39 x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 7);
40 x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 7);
41 x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 7);
42
43 x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 16);
44 x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 16);
45 x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 16);
46 x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 16);
47
48 x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 12);
49 x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 12);
50 x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 12);
51 x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 12);
52
53 x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 8);
54 x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 8);
55 x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 8);
56 x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 8);
57
58 x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 7);
59 x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 7);
60 x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 7);
61 x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 7);
62 }
63}
64
65/**
66 * chacha_block - generate one keystream block and increment block counter
67 * @state: input state matrix (16 32-bit words)
68 * @stream: output keystream block (64 bytes)
69 * @nrounds: number of rounds (20 or 12; 20 is recommended)
70 *
71 * This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
72 * The caller has already converted the endianness of the input. This function
73 * also handles incrementing the block counter in the input matrix.
74 */
75void chacha_block(u32 *state, u8 *stream, int nrounds)
76{
77 u32 x[16];
78 int i;
79
80 memcpy(x, state, 64);
81
82 chacha_permute(x, nrounds);
83
84 for (i = 0; i < ARRAY_SIZE(x); i++)
85 put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
86
87 state[12]++;
88}
89EXPORT_SYMBOL(chacha_block);
90
91/**
92 * hchacha_block - abbreviated ChaCha core, for XChaCha
93 * @in: input state matrix (16 32-bit words)
94 * @out: output (8 32-bit words)
95 * @nrounds: number of rounds (20 or 12; 20 is recommended)
96 *
97 * HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step
98 * towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). HChaCha
99 * skips the final addition of the initial state, and outputs only certain words
100 * of the state. It should not be used for streaming directly.
101 */
102void hchacha_block(const u32 *in, u32 *out, int nrounds)
103{
104 u32 x[16];
105
106 memcpy(x, in, 64);
107
108 chacha_permute(x, nrounds);
109
110 memcpy(&out[0], &x[0], 16);
111 memcpy(&out[4], &x[12], 16);
112}
113EXPORT_SYMBOL(hchacha_block);