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
31 struct salsa20_ctx {
32 u32 initial_state[16];
33 };
34
salsa20_block(u32 * state,__le32 * stream)35 static 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
salsa20_docrypt(u32 * state,u8 * dst,const u8 * src,unsigned int bytes)84 static 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 while (bytes >= SALSA20_BLOCK_SIZE) {
90 salsa20_block(state, stream);
91 crypto_xor_cpy(dst, src, (const u8 *)stream,
92 SALSA20_BLOCK_SIZE);
93 bytes -= SALSA20_BLOCK_SIZE;
94 dst += SALSA20_BLOCK_SIZE;
95 src += SALSA20_BLOCK_SIZE;
96 }
97 if (bytes) {
98 salsa20_block(state, stream);
99 crypto_xor_cpy(dst, src, (const u8 *)stream, bytes);
100 }
101 }
102
salsa20_init(u32 * state,const struct salsa20_ctx * ctx,const u8 * iv)103 static void salsa20_init(u32 *state, const struct salsa20_ctx *ctx,
104 const u8 *iv)
105 {
106 memcpy(state, ctx->initial_state, sizeof(ctx->initial_state));
107 state[6] = get_unaligned_le32(iv + 0);
108 state[7] = get_unaligned_le32(iv + 4);
109 }
110
salsa20_setkey(struct crypto_skcipher * tfm,const u8 * key,unsigned int keysize)111 static int salsa20_setkey(struct crypto_skcipher *tfm, const u8 *key,
112 unsigned int keysize)
113 {
114 static const char sigma[16] = "expand 32-byte k";
115 static const char tau[16] = "expand 16-byte k";
116 struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
117 const char *constants;
118
119 if (keysize != SALSA20_MIN_KEY_SIZE &&
120 keysize != SALSA20_MAX_KEY_SIZE)
121 return -EINVAL;
122
123 ctx->initial_state[1] = get_unaligned_le32(key + 0);
124 ctx->initial_state[2] = get_unaligned_le32(key + 4);
125 ctx->initial_state[3] = get_unaligned_le32(key + 8);
126 ctx->initial_state[4] = get_unaligned_le32(key + 12);
127 if (keysize == 32) { /* recommended */
128 key += 16;
129 constants = sigma;
130 } else { /* keysize == 16 */
131 constants = tau;
132 }
133 ctx->initial_state[11] = get_unaligned_le32(key + 0);
134 ctx->initial_state[12] = get_unaligned_le32(key + 4);
135 ctx->initial_state[13] = get_unaligned_le32(key + 8);
136 ctx->initial_state[14] = get_unaligned_le32(key + 12);
137 ctx->initial_state[0] = get_unaligned_le32(constants + 0);
138 ctx->initial_state[5] = get_unaligned_le32(constants + 4);
139 ctx->initial_state[10] = get_unaligned_le32(constants + 8);
140 ctx->initial_state[15] = get_unaligned_le32(constants + 12);
141
142 /* space for the nonce; it will be overridden for each request */
143 ctx->initial_state[6] = 0;
144 ctx->initial_state[7] = 0;
145
146 /* initial block number */
147 ctx->initial_state[8] = 0;
148 ctx->initial_state[9] = 0;
149
150 return 0;
151 }
152
salsa20_crypt(struct skcipher_request * req)153 static int salsa20_crypt(struct skcipher_request *req)
154 {
155 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
156 const struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
157 struct skcipher_walk walk;
158 u32 state[16];
159 int err;
160
161 err = skcipher_walk_virt(&walk, req, false);
162
163 salsa20_init(state, ctx, req->iv);
164
165 while (walk.nbytes > 0) {
166 unsigned int nbytes = walk.nbytes;
167
168 if (nbytes < walk.total)
169 nbytes = round_down(nbytes, walk.stride);
170
171 salsa20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
172 nbytes);
173 err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
174 }
175
176 return err;
177 }
178
179 static struct skcipher_alg alg = {
180 .base.cra_name = "salsa20",
181 .base.cra_driver_name = "salsa20-generic",
182 .base.cra_priority = 100,
183 .base.cra_blocksize = 1,
184 .base.cra_ctxsize = sizeof(struct salsa20_ctx),
185 .base.cra_module = THIS_MODULE,
186
187 .min_keysize = SALSA20_MIN_KEY_SIZE,
188 .max_keysize = SALSA20_MAX_KEY_SIZE,
189 .ivsize = SALSA20_IV_SIZE,
190 .chunksize = SALSA20_BLOCK_SIZE,
191 .setkey = salsa20_setkey,
192 .encrypt = salsa20_crypt,
193 .decrypt = salsa20_crypt,
194 };
195
salsa20_generic_mod_init(void)196 static int __init salsa20_generic_mod_init(void)
197 {
198 return crypto_register_skcipher(&alg);
199 }
200
salsa20_generic_mod_fini(void)201 static void __exit salsa20_generic_mod_fini(void)
202 {
203 crypto_unregister_skcipher(&alg);
204 }
205
206 subsys_initcall(salsa20_generic_mod_init);
207 module_exit(salsa20_generic_mod_fini);
208
209 MODULE_LICENSE("GPL");
210 MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
211 MODULE_ALIAS_CRYPTO("salsa20");
212 MODULE_ALIAS_CRYPTO("salsa20-generic");
213