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 /*
  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
  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
 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
 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
 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
 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
 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_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
 236 static int __init salsa20_generic_mod_init(void)
 237 {
 238         return crypto_register_alg(&alg);
 239 }
 240
 241 static void __exit salsa20_generic_mod_fini(void)
 242 {
 243         crypto_unregister_alg(&alg);
 244 }
 245
 246 module_init(salsa20_generic_mod_init);
 247 module_exit(salsa20_generic_mod_fini);
 248
 249 MODULE_LICENSE("GPL");
 250 MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
 251 MODULE_ALIAS("salsa20");