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Linux/crypto/salsa20_generic.c

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  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 
 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 
 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         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 
104 static 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 
112 static 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 
154 static 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, true);
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 
180 static 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 
197 static int __init salsa20_generic_mod_init(void)
198 {
199         return crypto_register_skcipher(&alg);
200 }
201 
202 static void __exit salsa20_generic_mod_fini(void)
203 {
204         crypto_unregister_skcipher(&alg);
205 }
206 
207 module_init(salsa20_generic_mod_init);
208 module_exit(salsa20_generic_mod_fini);
209 
210 MODULE_LICENSE("GPL");
211 MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
212 MODULE_ALIAS_CRYPTO("salsa20");
213 MODULE_ALIAS_CRYPTO("salsa20-generic");
214 

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