1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Common values and helper functions for the ChaCha and XChaCha stream ciphers.
4 *
5 * XChaCha extends ChaCha's nonce to 192 bits, while provably retaining ChaCha's
6 * security. Here they share the same key size, tfm context, and setkey
7 * function; only their IV size and encrypt/decrypt function differ.
8 *
9 * The ChaCha paper specifies 20, 12, and 8-round variants. In general, it is
10 * recommended to use the 20-round variant ChaCha20. However, the other
11 * variants can be needed in some performance-sensitive scenarios. The generic
12 * ChaCha code currently allows only the 20 and 12-round variants.
13 */
14
15#ifndef _CRYPTO_CHACHA_H
16#define _CRYPTO_CHACHA_H
17
18#include <linux/unaligned.h>
19#include <linux/string.h>
20#include <linux/types.h>
21
22/* 32-bit stream position, then 96-bit nonce (RFC7539 convention) */
23#define CHACHA_IV_SIZE 16
24
25#define CHACHA_KEY_SIZE 32
26#define CHACHA_BLOCK_SIZE 64
27#define CHACHAPOLY_IV_SIZE 12
28
29#define CHACHA_KEY_WORDS 8
30#define CHACHA_STATE_WORDS 16
31#define HCHACHA_OUT_WORDS 8
32
33/* 192-bit nonce, then 64-bit stream position */
34#define XCHACHA_IV_SIZE 32
35
36struct chacha_state {
37 u32 x[CHACHA_STATE_WORDS];
38};
39
40void chacha_block_generic(struct chacha_state *state,
41 u8 out[at_least CHACHA_BLOCK_SIZE], int nrounds);
42static inline void chacha20_block(struct chacha_state *state,
43 u8 out[at_least CHACHA_BLOCK_SIZE])
44{
45 chacha_block_generic(state, out, nrounds: 20);
46}
47
48void hchacha_block_generic(const struct chacha_state *state,
49 u32 out[at_least HCHACHA_OUT_WORDS], int nrounds);
50
51void hchacha_block(const struct chacha_state *state,
52 u32 out[at_least HCHACHA_OUT_WORDS], int nrounds);
53
54enum chacha_constants { /* expand 32-byte k */
55 CHACHA_CONSTANT_EXPA = 0x61707865U,
56 CHACHA_CONSTANT_ND_3 = 0x3320646eU,
57 CHACHA_CONSTANT_2_BY = 0x79622d32U,
58 CHACHA_CONSTANT_TE_K = 0x6b206574U
59};
60
61static inline void chacha_init_consts(struct chacha_state *state)
62{
63 state->x[0] = CHACHA_CONSTANT_EXPA;
64 state->x[1] = CHACHA_CONSTANT_ND_3;
65 state->x[2] = CHACHA_CONSTANT_2_BY;
66 state->x[3] = CHACHA_CONSTANT_TE_K;
67}
68
69static inline void chacha_init(struct chacha_state *state,
70 const u32 key[at_least CHACHA_KEY_WORDS],
71 const u8 iv[at_least CHACHA_IV_SIZE])
72{
73 chacha_init_consts(state);
74 state->x[4] = key[0];
75 state->x[5] = key[1];
76 state->x[6] = key[2];
77 state->x[7] = key[3];
78 state->x[8] = key[4];
79 state->x[9] = key[5];
80 state->x[10] = key[6];
81 state->x[11] = key[7];
82 state->x[12] = get_unaligned_le32(p: iv + 0);
83 state->x[13] = get_unaligned_le32(p: iv + 4);
84 state->x[14] = get_unaligned_le32(p: iv + 8);
85 state->x[15] = get_unaligned_le32(p: iv + 12);
86}
87
88void chacha_crypt(struct chacha_state *state, u8 *dst, const u8 *src,
89 unsigned int bytes, int nrounds);
90
91static inline void chacha20_crypt(struct chacha_state *state,
92 u8 *dst, const u8 *src, unsigned int bytes)
93{
94 chacha_crypt(state, dst, src, bytes, nrounds: 20);
95}
96
97static inline void chacha_zeroize_state(struct chacha_state *state)
98{
99 memzero_explicit(s: state, count: sizeof(*state));
100}
101
102#endif /* _CRYPTO_CHACHA_H */
103

source code of linux/include/crypto/chacha.h