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 /*
41 salsa20-ref.c version 20051118
42 D. J. Bernstein
43 Public 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
53 struct salsa20_ctx
54 {
55 u32 input[16];
56 };
57
salsa20_wordtobyte(u8 output[64],const u32 input[16])58 static 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
104 static const char sigma[16] = "expand 32-byte k";
105 static const char tau[16] = "expand 16-byte k";
106
salsa20_keysetup(struct salsa20_ctx * ctx,const u8 * k,u32 kbytes)107 static 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
salsa20_ivsetup(struct salsa20_ctx * ctx,const u8 * iv)131 static 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
salsa20_encrypt_bytes(struct salsa20_ctx * ctx,u8 * dst,const u8 * src,unsigned int bytes)139 static 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
setkey(struct crypto_tfm * tfm,const u8 * key,unsigned int keysize)169 static 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
encrypt(struct blkcipher_desc * desc,struct scatterlist * dst,struct scatterlist * src,unsigned int nbytes)177 static 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
214 static 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_list = LIST_HEAD_INIT(alg.cra_list),
225 .cra_u = {
226 .blkcipher = {
227 .setkey = setkey,
228 .encrypt = encrypt,
229 .decrypt = encrypt,
230 .min_keysize = SALSA20_MIN_KEY_SIZE,
231 .max_keysize = SALSA20_MAX_KEY_SIZE,
232 .ivsize = SALSA20_IV_SIZE,
233 }
234 }
235 };
236
salsa20_generic_mod_init(void)237 static int __init salsa20_generic_mod_init(void)
238 {
239 return crypto_register_alg(&alg);
240 }
241
salsa20_generic_mod_fini(void)242 static void __exit salsa20_generic_mod_fini(void)
243 {
244 crypto_unregister_alg(&alg);
245 }
246
247 module_init(salsa20_generic_mod_init);
248 module_exit(salsa20_generic_mod_fini);
249
250 MODULE_LICENSE("GPL");
251 MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
252 MODULE_ALIAS("salsa20");
253