Root/crypto/salsa20_generic.c

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 <linux/init.h>
23#include <linux/module.h>
24#include <linux/errno.h>
25#include <linux/crypto.h>
26#include <linux/types.h>
27#include <linux/bitops.h>
28#include <crypto/algapi.h>
29#include <asm/byteorder.h>
30
31#define SALSA20_IV_SIZE 8U
32#define SALSA20_MIN_KEY_SIZE 16U
33#define SALSA20_MAX_KEY_SIZE 32U
34
35/*
36 * Start of code taken from D. J. Bernstein's reference implementation.
37 * With some modifications and optimizations made to suit our needs.
38 */
39
40/*
41salsa20-ref.c version 20051118
42D. J. Bernstein
43Public domain.
44*/
45
46#define U32TO8_LITTLE(p, v) \
47    { (p)[0] = (v >> 0) & 0xff; (p)[1] = (v >> 8) & 0xff; \
48      (p)[2] = (v >> 16) & 0xff; (p)[3] = (v >> 24) & 0xff; }
49#define U8TO32_LITTLE(p) \
50    (((u32)((p)[0]) ) | ((u32)((p)[1]) << 8) | \
51     ((u32)((p)[2]) << 16) | ((u32)((p)[3]) << 24) )
52
53struct salsa20_ctx
54{
55    u32 input[16];
56};
57
58static void salsa20_wordtobyte(u8 output[64], const u32 input[16])
59{
60    u32 x[16];
61    int i;
62
63    memcpy(x, input, sizeof(x));
64    for (i = 20; i > 0; i -= 2) {
65        x[ 4] ^= rol32((x[ 0] + x[12]), 7);
66        x[ 8] ^= rol32((x[ 4] + x[ 0]), 9);
67        x[12] ^= rol32((x[ 8] + x[ 4]), 13);
68        x[ 0] ^= rol32((x[12] + x[ 8]), 18);
69        x[ 9] ^= rol32((x[ 5] + x[ 1]), 7);
70        x[13] ^= rol32((x[ 9] + x[ 5]), 9);
71        x[ 1] ^= rol32((x[13] + x[ 9]), 13);
72        x[ 5] ^= rol32((x[ 1] + x[13]), 18);
73        x[14] ^= rol32((x[10] + x[ 6]), 7);
74        x[ 2] ^= rol32((x[14] + x[10]), 9);
75        x[ 6] ^= rol32((x[ 2] + x[14]), 13);
76        x[10] ^= rol32((x[ 6] + x[ 2]), 18);
77        x[ 3] ^= rol32((x[15] + x[11]), 7);
78        x[ 7] ^= rol32((x[ 3] + x[15]), 9);
79        x[11] ^= rol32((x[ 7] + x[ 3]), 13);
80        x[15] ^= rol32((x[11] + x[ 7]), 18);
81        x[ 1] ^= rol32((x[ 0] + x[ 3]), 7);
82        x[ 2] ^= rol32((x[ 1] + x[ 0]), 9);
83        x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
84        x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
85        x[ 6] ^= rol32((x[ 5] + x[ 4]), 7);
86        x[ 7] ^= rol32((x[ 6] + x[ 5]), 9);
87        x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
88        x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
89        x[11] ^= rol32((x[10] + x[ 9]), 7);
90        x[ 8] ^= rol32((x[11] + x[10]), 9);
91        x[ 9] ^= rol32((x[ 8] + x[11]), 13);
92        x[10] ^= rol32((x[ 9] + x[ 8]), 18);
93        x[12] ^= rol32((x[15] + x[14]), 7);
94        x[13] ^= rol32((x[12] + x[15]), 9);
95        x[14] ^= rol32((x[13] + x[12]), 13);
96        x[15] ^= rol32((x[14] + x[13]), 18);
97    }
98    for (i = 0; i < 16; ++i)
99        x[i] += input[i];
100    for (i = 0; i < 16; ++i)
101        U32TO8_LITTLE(output + 4 * i,x[i]);
102}
103
104static const char sigma[16] = "expand 32-byte k";
105static const char tau[16] = "expand 16-byte k";
106
107static void salsa20_keysetup(struct salsa20_ctx *ctx, const u8 *k, u32 kbytes)
108{
109    const char *constants;
110
111    ctx->input[1] = U8TO32_LITTLE(k + 0);
112    ctx->input[2] = U8TO32_LITTLE(k + 4);
113    ctx->input[3] = U8TO32_LITTLE(k + 8);
114    ctx->input[4] = U8TO32_LITTLE(k + 12);
115    if (kbytes == 32) { /* recommended */
116        k += 16;
117        constants = sigma;
118    } else { /* kbytes == 16 */
119        constants = tau;
120    }
121    ctx->input[11] = U8TO32_LITTLE(k + 0);
122    ctx->input[12] = U8TO32_LITTLE(k + 4);
123    ctx->input[13] = U8TO32_LITTLE(k + 8);
124    ctx->input[14] = U8TO32_LITTLE(k + 12);
125    ctx->input[0] = U8TO32_LITTLE(constants + 0);
126    ctx->input[5] = U8TO32_LITTLE(constants + 4);
127    ctx->input[10] = U8TO32_LITTLE(constants + 8);
128    ctx->input[15] = U8TO32_LITTLE(constants + 12);
129}
130
131static void salsa20_ivsetup(struct salsa20_ctx *ctx, const u8 *iv)
132{
133    ctx->input[6] = U8TO32_LITTLE(iv + 0);
134    ctx->input[7] = U8TO32_LITTLE(iv + 4);
135    ctx->input[8] = 0;
136    ctx->input[9] = 0;
137}
138
139static void salsa20_encrypt_bytes(struct salsa20_ctx *ctx, u8 *dst,
140                  const u8 *src, unsigned int bytes)
141{
142    u8 buf[64];
143
144    if (dst != src)
145        memcpy(dst, src, bytes);
146
147    while (bytes) {
148        salsa20_wordtobyte(buf, ctx->input);
149
150        ctx->input[8]++;
151        if (!ctx->input[8])
152            ctx->input[9]++;
153
154        if (bytes <= 64) {
155            crypto_xor(dst, buf, bytes);
156            return;
157        }
158
159        crypto_xor(dst, buf, 64);
160        bytes -= 64;
161        dst += 64;
162    }
163}
164
165/*
166 * End of code taken from D. J. Bernstein's reference implementation.
167 */
168
169static int setkey(struct crypto_tfm *tfm, const u8 *key,
170          unsigned int keysize)
171{
172    struct salsa20_ctx *ctx = crypto_tfm_ctx(tfm);
173    salsa20_keysetup(ctx, key, keysize);
174    return 0;
175}
176
177static int encrypt(struct blkcipher_desc *desc,
178           struct scatterlist *dst, struct scatterlist *src,
179           unsigned int nbytes)
180{
181    struct blkcipher_walk walk;
182    struct crypto_blkcipher *tfm = desc->tfm;
183    struct salsa20_ctx *ctx = crypto_blkcipher_ctx(tfm);
184    int err;
185
186    blkcipher_walk_init(&walk, dst, src, nbytes);
187    err = blkcipher_walk_virt_block(desc, &walk, 64);
188
189    salsa20_ivsetup(ctx, walk.iv);
190
191    if (likely(walk.nbytes == nbytes))
192    {
193        salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
194                      walk.src.virt.addr, nbytes);
195        return blkcipher_walk_done(desc, &walk, 0);
196    }
197
198    while (walk.nbytes >= 64) {
199        salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
200                      walk.src.virt.addr,
201                      walk.nbytes - (walk.nbytes % 64));
202        err = blkcipher_walk_done(desc, &walk, walk.nbytes % 64);
203    }
204
205    if (walk.nbytes) {
206        salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
207                      walk.src.virt.addr, walk.nbytes);
208        err = blkcipher_walk_done(desc, &walk, 0);
209    }
210
211    return err;
212}
213
214static struct crypto_alg alg = {
215    .cra_name = "salsa20",
216    .cra_driver_name = "salsa20-generic",
217    .cra_priority = 100,
218    .cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER,
219    .cra_type = &crypto_blkcipher_type,
220    .cra_blocksize = 1,
221    .cra_ctxsize = sizeof(struct salsa20_ctx),
222    .cra_alignmask = 3,
223    .cra_module = THIS_MODULE,
224    .cra_u = {
225        .blkcipher = {
226            .setkey = setkey,
227            .encrypt = encrypt,
228            .decrypt = encrypt,
229            .min_keysize = SALSA20_MIN_KEY_SIZE,
230            .max_keysize = SALSA20_MAX_KEY_SIZE,
231            .ivsize = SALSA20_IV_SIZE,
232        }
233    }
234};
235
236static int __init salsa20_generic_mod_init(void)
237{
238    return crypto_register_alg(&alg);
239}
240
241static void __exit salsa20_generic_mod_fini(void)
242{
243    crypto_unregister_alg(&alg);
244}
245
246module_init(salsa20_generic_mod_init);
247module_exit(salsa20_generic_mod_fini);
248
249MODULE_LICENSE("GPL");
250MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
251MODULE_ALIAS("salsa20");
252

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