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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 <crypto/chacha.h>
9#include <linux/bitops.h>
10#include <linux/bug.h>
11#include <linux/export.h>
12#include <linux/kernel.h>
13#include <linux/string.h>
14#include <linux/unaligned.h>
15
16static void chacha_permute(struct chacha_state *state, int nrounds)
17{
18 u32 *x = state->x;
19 int i;
20
21 /* whitelist the allowed round counts */
22 WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
23
24 for (i = 0; i < nrounds; i += 2) {
25 x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 16);
26 x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 16);
27 x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 16);
28 x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 16);
29
30 x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 12);
31 x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 12);
32 x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 12);
33 x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 12);
34
35 x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 8);
36 x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 8);
37 x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 8);
38 x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 8);
39
40 x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 7);
41 x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 7);
42 x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 7);
43 x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 7);
44
45 x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 16);
46 x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 16);
47 x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 16);
48 x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 16);
49
50 x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 12);
51 x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 12);
52 x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 12);
53 x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 12);
54
55 x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 8);
56 x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 8);
57 x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 8);
58 x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 8);
59
60 x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 7);
61 x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 7);
62 x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 7);
63 x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 7);
64 }
65}
66
67/**
68 * chacha_block_generic - generate one keystream block and increment block counter
69 * @state: input state matrix
70 * @out: output keystream block
71 * @nrounds: number of rounds (20 or 12; 20 is recommended)
72 *
73 * This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
74 * The caller has already converted the endianness of the input. This function
75 * also handles incrementing the block counter in the input matrix.
76 */
77void chacha_block_generic(struct chacha_state *state,
78 u8 out[CHACHA_BLOCK_SIZE], int nrounds)
79{
80 struct chacha_state permuted_state = *state;
81 int i;
82
83 chacha_permute(&permuted_state, nrounds);
84
85 for (i = 0; i < ARRAY_SIZE(state->x); i++)
86 put_unaligned_le32(permuted_state.x[i] + state->x[i],
87 &out[i * sizeof(u32)]);
88
89 state->x[12]++;
90
91 chacha_zeroize_state(&permuted_state);
92}
93EXPORT_SYMBOL(chacha_block_generic);
94
95/**
96 * hchacha_block_generic - abbreviated ChaCha core, for XChaCha
97 * @state: input state matrix
98 * @out: the output words
99 * @nrounds: number of rounds (20 or 12; 20 is recommended)
100 *
101 * HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step
102 * towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). HChaCha
103 * skips the final addition of the initial state, and outputs only certain words
104 * of the state. It should not be used for streaming directly.
105 */
106void hchacha_block_generic(const struct chacha_state *state,
107 u32 out[HCHACHA_OUT_WORDS], int nrounds)
108{
109 struct chacha_state permuted_state = *state;
110
111 chacha_permute(&permuted_state, nrounds);
112
113 memcpy(&out[0], &permuted_state.x[0], 16);
114 memcpy(&out[4], &permuted_state.x[12], 16);
115
116 chacha_zeroize_state(&permuted_state);
117}
118EXPORT_SYMBOL(hchacha_block_generic);