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