1/*
2 * Salsa20: Salsa20 stream cipher algorithm
3 *
4 * Copyright (c) 2007 Tan Swee Heng <thesweeheng@gmail.com>
5 *
6 * Derived from:
7 * - salsa20.c: Public domain C code by Daniel J. Bernstein <djb@cr.yp.to>
8 *
9 * Salsa20 is a stream cipher candidate in eSTREAM, the ECRYPT Stream
10 * Cipher Project. It is designed by Daniel J. Bernstein <djb@cr.yp.to>.
11 * More information about eSTREAM and Salsa20 can be found here:
12 * http://www.ecrypt.eu.org/stream/
13 * http://cr.yp.to/snuffle.html
14 *
15 * This program is free software; you can redistribute it and/or modify it
16 * under the terms of the GNU General Public License as published by the Free
17 * Software Foundation; either version 2 of the License, or (at your option)
18 * any later version.
19 *
20 */
21
22#include <asm/unaligned.h>
23#include <crypto/internal/skcipher.h>
24#include <linux/module.h>
25
26#define SALSA20_IV_SIZE 8
27#define SALSA20_MIN_KEY_SIZE 16
28#define SALSA20_MAX_KEY_SIZE 32
29#define SALSA20_BLOCK_SIZE 64
30
31struct salsa20_ctx {
32 u32 initial_state[16];
33};
34
35static void salsa20_block(u32 *state, __le32 *stream)
36{
37 u32 x[16];
38 int i;
39
40 memcpy(x, state, sizeof(x));
41
42 for (i = 0; i < 20; i += 2) {
43 x[ 4] ^= rol32((x[ 0] + x[12]), 7);
44 x[ 8] ^= rol32((x[ 4] + x[ 0]), 9);
45 x[12] ^= rol32((x[ 8] + x[ 4]), 13);
46 x[ 0] ^= rol32((x[12] + x[ 8]), 18);
47 x[ 9] ^= rol32((x[ 5] + x[ 1]), 7);
48 x[13] ^= rol32((x[ 9] + x[ 5]), 9);
49 x[ 1] ^= rol32((x[13] + x[ 9]), 13);
50 x[ 5] ^= rol32((x[ 1] + x[13]), 18);
51 x[14] ^= rol32((x[10] + x[ 6]), 7);
52 x[ 2] ^= rol32((x[14] + x[10]), 9);
53 x[ 6] ^= rol32((x[ 2] + x[14]), 13);
54 x[10] ^= rol32((x[ 6] + x[ 2]), 18);
55 x[ 3] ^= rol32((x[15] + x[11]), 7);
56 x[ 7] ^= rol32((x[ 3] + x[15]), 9);
57 x[11] ^= rol32((x[ 7] + x[ 3]), 13);
58 x[15] ^= rol32((x[11] + x[ 7]), 18);
59 x[ 1] ^= rol32((x[ 0] + x[ 3]), 7);
60 x[ 2] ^= rol32((x[ 1] + x[ 0]), 9);
61 x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
62 x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
63 x[ 6] ^= rol32((x[ 5] + x[ 4]), 7);
64 x[ 7] ^= rol32((x[ 6] + x[ 5]), 9);
65 x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
66 x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
67 x[11] ^= rol32((x[10] + x[ 9]), 7);
68 x[ 8] ^= rol32((x[11] + x[10]), 9);
69 x[ 9] ^= rol32((x[ 8] + x[11]), 13);
70 x[10] ^= rol32((x[ 9] + x[ 8]), 18);
71 x[12] ^= rol32((x[15] + x[14]), 7);
72 x[13] ^= rol32((x[12] + x[15]), 9);
73 x[14] ^= rol32((x[13] + x[12]), 13);
74 x[15] ^= rol32((x[14] + x[13]), 18);
75 }
76
77 for (i = 0; i < 16; i++)
78 stream[i] = cpu_to_le32(x[i] + state[i]);
79
80 if (++state[8] == 0)
81 state[9]++;
82}
83
84static void salsa20_docrypt(u32 *state, u8 *dst, const u8 *src,
85 unsigned int bytes)
86{
87 __le32 stream[SALSA20_BLOCK_SIZE / sizeof(__le32)];
88
89 if (dst != src)
90 memcpy(dst, src, bytes);
91
92 while (bytes >= SALSA20_BLOCK_SIZE) {
93 salsa20_block(state, stream);
94 crypto_xor(dst, (const u8 *)stream, SALSA20_BLOCK_SIZE);
95 bytes -= SALSA20_BLOCK_SIZE;
96 dst += SALSA20_BLOCK_SIZE;
97 }
98 if (bytes) {
99 salsa20_block(state, stream);
100 crypto_xor(dst, (const u8 *)stream, bytes);
101 }
102}
103
104static void salsa20_init(u32 *state, const struct salsa20_ctx *ctx,
105 const u8 *iv)
106{
107 memcpy(state, ctx->initial_state, sizeof(ctx->initial_state));
108 state[6] = get_unaligned_le32(iv + 0);
109 state[7] = get_unaligned_le32(iv + 4);
110}
111
112static int salsa20_setkey(struct crypto_skcipher *tfm, const u8 *key,
113 unsigned int keysize)
114{
115 static const char sigma[16] = "expand 32-byte k";
116 static const char tau[16] = "expand 16-byte k";
117 struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
118 const char *constants;
119
120 if (keysize != SALSA20_MIN_KEY_SIZE &&
121 keysize != SALSA20_MAX_KEY_SIZE)
122 return -EINVAL;
123
124 ctx->initial_state[1] = get_unaligned_le32(key + 0);
125 ctx->initial_state[2] = get_unaligned_le32(key + 4);
126 ctx->initial_state[3] = get_unaligned_le32(key + 8);
127 ctx->initial_state[4] = get_unaligned_le32(key + 12);
128 if (keysize == 32) { /* recommended */
129 key += 16;
130 constants = sigma;
131 } else { /* keysize == 16 */
132 constants = tau;
133 }
134 ctx->initial_state[11] = get_unaligned_le32(key + 0);
135 ctx->initial_state[12] = get_unaligned_le32(key + 4);
136 ctx->initial_state[13] = get_unaligned_le32(key + 8);
137 ctx->initial_state[14] = get_unaligned_le32(key + 12);
138 ctx->initial_state[0] = get_unaligned_le32(constants + 0);
139 ctx->initial_state[5] = get_unaligned_le32(constants + 4);
140 ctx->initial_state[10] = get_unaligned_le32(constants + 8);
141 ctx->initial_state[15] = get_unaligned_le32(constants + 12);
142
143 /* space for the nonce; it will be overridden for each request */
144 ctx->initial_state[6] = 0;
145 ctx->initial_state[7] = 0;
146
147 /* initial block number */
148 ctx->initial_state[8] = 0;
149 ctx->initial_state[9] = 0;
150
151 return 0;
152}
153
154static int salsa20_crypt(struct skcipher_request *req)
155{
156 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
157 const struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
158 struct skcipher_walk walk;
159 u32 state[16];
160 int err;
161
162 err = skcipher_walk_virt(&walk, req, false);
163
164 salsa20_init(state, ctx, walk.iv);
165
166 while (walk.nbytes > 0) {
167 unsigned int nbytes = walk.nbytes;
168
169 if (nbytes < walk.total)
170 nbytes = round_down(nbytes, walk.stride);
171
172 salsa20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
173 nbytes);
174 err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
175 }
176
177 return err;
178}
179
180static struct skcipher_alg alg = {
181 .base.cra_name = "salsa20",
182 .base.cra_driver_name = "salsa20-generic",
183 .base.cra_priority = 100,
184 .base.cra_blocksize = 1,
185 .base.cra_ctxsize = sizeof(struct salsa20_ctx),
186 .base.cra_module = THIS_MODULE,
187
188 .min_keysize = SALSA20_MIN_KEY_SIZE,
189 .max_keysize = SALSA20_MAX_KEY_SIZE,
190 .ivsize = SALSA20_IV_SIZE,
191 .chunksize = SALSA20_BLOCK_SIZE,
192 .setkey = salsa20_setkey,
193 .encrypt = salsa20_crypt,
194 .decrypt = salsa20_crypt,
195};
196
197static int __init salsa20_generic_mod_init(void)
198{
199 return crypto_register_skcipher(&alg);
200}
201
202static void __exit salsa20_generic_mod_fini(void)
203{
204 crypto_unregister_skcipher(&alg);
205}
206
207module_init(salsa20_generic_mod_init);
208module_exit(salsa20_generic_mod_fini);
209
210MODULE_LICENSE("GPL");
211MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
212MODULE_ALIAS_CRYPTO("salsa20");
213MODULE_ALIAS_CRYPTO("salsa20-generic");
214