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 <crypto/salsa20.h>
  25#include <linux/module.h>
  26
  27static void salsa20_block(u32 *state, __le32 *stream)
  28{
  29        u32 x[16];
  30        int i;
  31
  32        memcpy(x, state, sizeof(x));
  33
  34        for (i = 0; i < 20; i += 2) {
  35                x[ 4] ^= rol32((x[ 0] + x[12]),  7);
  36                x[ 8] ^= rol32((x[ 4] + x[ 0]),  9);
  37                x[12] ^= rol32((x[ 8] + x[ 4]), 13);
  38                x[ 0] ^= rol32((x[12] + x[ 8]), 18);
  39                x[ 9] ^= rol32((x[ 5] + x[ 1]),  7);
  40                x[13] ^= rol32((x[ 9] + x[ 5]),  9);
  41                x[ 1] ^= rol32((x[13] + x[ 9]), 13);
  42                x[ 5] ^= rol32((x[ 1] + x[13]), 18);
  43                x[14] ^= rol32((x[10] + x[ 6]),  7);
  44                x[ 2] ^= rol32((x[14] + x[10]),  9);
  45                x[ 6] ^= rol32((x[ 2] + x[14]), 13);
  46                x[10] ^= rol32((x[ 6] + x[ 2]), 18);
  47                x[ 3] ^= rol32((x[15] + x[11]),  7);
  48                x[ 7] ^= rol32((x[ 3] + x[15]),  9);
  49                x[11] ^= rol32((x[ 7] + x[ 3]), 13);
  50                x[15] ^= rol32((x[11] + x[ 7]), 18);
  51                x[ 1] ^= rol32((x[ 0] + x[ 3]),  7);
  52                x[ 2] ^= rol32((x[ 1] + x[ 0]),  9);
  53                x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
  54                x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
  55                x[ 6] ^= rol32((x[ 5] + x[ 4]),  7);
  56                x[ 7] ^= rol32((x[ 6] + x[ 5]),  9);
  57                x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
  58                x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
  59                x[11] ^= rol32((x[10] + x[ 9]),  7);
  60                x[ 8] ^= rol32((x[11] + x[10]),  9);
  61                x[ 9] ^= rol32((x[ 8] + x[11]), 13);
  62                x[10] ^= rol32((x[ 9] + x[ 8]), 18);
  63                x[12] ^= rol32((x[15] + x[14]),  7);
  64                x[13] ^= rol32((x[12] + x[15]),  9);
  65                x[14] ^= rol32((x[13] + x[12]), 13);
  66                x[15] ^= rol32((x[14] + x[13]), 18);
  67        }
  68
  69        for (i = 0; i < 16; i++)
  70                stream[i] = cpu_to_le32(x[i] + state[i]);
  71
  72        if (++state[8] == 0)
  73                state[9]++;
  74}
  75
  76static void salsa20_docrypt(u32 *state, u8 *dst, const u8 *src,
  77                            unsigned int bytes)
  78{
  79        __le32 stream[SALSA20_BLOCK_SIZE / sizeof(__le32)];
  80
  81        if (dst != src)
  82                memcpy(dst, src, bytes);
  83
  84        while (bytes >= SALSA20_BLOCK_SIZE) {
  85                salsa20_block(state, stream);
  86                crypto_xor(dst, (const u8 *)stream, SALSA20_BLOCK_SIZE);
  87                bytes -= SALSA20_BLOCK_SIZE;
  88                dst += SALSA20_BLOCK_SIZE;
  89        }
  90        if (bytes) {
  91                salsa20_block(state, stream);
  92                crypto_xor(dst, (const u8 *)stream, bytes);
  93        }
  94}
  95
  96void crypto_salsa20_init(u32 *state, const struct salsa20_ctx *ctx,
  97                         const u8 *iv)
  98{
  99        memcpy(state, ctx->initial_state, sizeof(ctx->initial_state));
 100        state[6] = get_unaligned_le32(iv + 0);
 101        state[7] = get_unaligned_le32(iv + 4);
 102}
 103EXPORT_SYMBOL_GPL(crypto_salsa20_init);
 104
 105int crypto_salsa20_setkey(struct crypto_skcipher *tfm, const u8 *key,
 106                          unsigned int keysize)
 107{
 108        static const char sigma[16] = "expand 32-byte k";
 109        static const char tau[16] = "expand 16-byte k";
 110        struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
 111        const char *constants;
 112
 113        if (keysize != SALSA20_MIN_KEY_SIZE &&
 114            keysize != SALSA20_MAX_KEY_SIZE)
 115                return -EINVAL;
 116
 117        ctx->initial_state[1] = get_unaligned_le32(key + 0);
 118        ctx->initial_state[2] = get_unaligned_le32(key + 4);
 119        ctx->initial_state[3] = get_unaligned_le32(key + 8);
 120        ctx->initial_state[4] = get_unaligned_le32(key + 12);
 121        if (keysize == 32) { /* recommended */
 122                key += 16;
 123                constants = sigma;
 124        } else { /* keysize == 16 */
 125                constants = tau;
 126        }
 127        ctx->initial_state[11] = get_unaligned_le32(key + 0);
 128        ctx->initial_state[12] = get_unaligned_le32(key + 4);
 129        ctx->initial_state[13] = get_unaligned_le32(key + 8);
 130        ctx->initial_state[14] = get_unaligned_le32(key + 12);
 131        ctx->initial_state[0]  = get_unaligned_le32(constants + 0);
 132        ctx->initial_state[5]  = get_unaligned_le32(constants + 4);
 133        ctx->initial_state[10] = get_unaligned_le32(constants + 8);
 134        ctx->initial_state[15] = get_unaligned_le32(constants + 12);
 135
 136        /* space for the nonce; it will be overridden for each request */
 137        ctx->initial_state[6] = 0;
 138        ctx->initial_state[7] = 0;
 139
 140        /* initial block number */
 141        ctx->initial_state[8] = 0;
 142        ctx->initial_state[9] = 0;
 143
 144        return 0;
 145}
 146EXPORT_SYMBOL_GPL(crypto_salsa20_setkey);
 147
 148static int salsa20_crypt(struct skcipher_request *req)
 149{
 150        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 151        const struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
 152        struct skcipher_walk walk;
 153        u32 state[16];
 154        int err;
 155
 156        err = skcipher_walk_virt(&walk, req, true);
 157
 158        crypto_salsa20_init(state, ctx, walk.iv);
 159
 160        while (walk.nbytes > 0) {
 161                unsigned int nbytes = walk.nbytes;
 162
 163                if (nbytes < walk.total)
 164                        nbytes = round_down(nbytes, walk.stride);
 165
 166                salsa20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
 167                                nbytes);
 168                err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
 169        }
 170
 171        return err;
 172}
 173
 174static struct skcipher_alg alg = {
 175        .base.cra_name          = "salsa20",
 176        .base.cra_driver_name   = "salsa20-generic",
 177        .base.cra_priority      = 100,
 178        .base.cra_blocksize     = 1,
 179        .base.cra_ctxsize       = sizeof(struct salsa20_ctx),
 180        .base.cra_module        = THIS_MODULE,
 181
 182        .min_keysize            = SALSA20_MIN_KEY_SIZE,
 183        .max_keysize            = SALSA20_MAX_KEY_SIZE,
 184        .ivsize                 = SALSA20_IV_SIZE,
 185        .chunksize              = SALSA20_BLOCK_SIZE,
 186        .setkey                 = crypto_salsa20_setkey,
 187        .encrypt                = salsa20_crypt,
 188        .decrypt                = salsa20_crypt,
 189};
 190
 191static int __init salsa20_generic_mod_init(void)
 192{
 193        return crypto_register_skcipher(&alg);
 194}
 195
 196static void __exit salsa20_generic_mod_fini(void)
 197{
 198        crypto_unregister_skcipher(&alg);
 199}
 200
 201module_init(salsa20_generic_mod_init);
 202module_exit(salsa20_generic_mod_fini);
 203
 204MODULE_LICENSE("GPL");
 205MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
 206MODULE_ALIAS_CRYPTO("salsa20");
 207MODULE_ALIAS_CRYPTO("salsa20-generic");
 208