salsa20_generic.c

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/*
 * Salsa20: Salsa20 stream cipher algorithm
 *
 * Copyright (c) 2007 Tan Swee Heng <[email protected]>
 *
 * Derived from:
 * - salsa20.c: Public domain C code by Daniel J. Bernstein <[email protected]>
 *
 * Salsa20 is a stream cipher candidate in eSTREAM, the ECRYPT Stream
 * Cipher Project. It is designed by Daniel J. Bernstein <[email protected]>.
 * More information about eSTREAM and Salsa20 can be found here:
 *   http://www.ecrypt.eu.org/stream/
 *   http://cr.yp.to/snuffle.html
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/crypto.h>
#include <linux/types.h>
#include <linux/bitops.h>
#include <crypto/algapi.h>
#include <asm/byteorder.h>

#define SALSA20_IV_SIZE        8U
#define SALSA20_MIN_KEY_SIZE  16U
#define SALSA20_MAX_KEY_SIZE  32U

/*
 * Start of code taken from D. J. Bernstein's reference implementation.
 * With some modifications and optimizations made to suit our needs.
 */

/*
salsa20-ref.c version 20051118
D. J. Bernstein
Public domain.
*/

#define U32TO8_LITTLE(p, v) \
    { (p)[0] = (v >>  0) & 0xff; (p)[1] = (v >>  8) & 0xff; \
      (p)[2] = (v >> 16) & 0xff; (p)[3] = (v >> 24) & 0xff; }
#define U8TO32_LITTLE(p)   \
    (((u32)((p)[0])      ) | ((u32)((p)[1]) <<  8) | \
     ((u32)((p)[2]) << 16) | ((u32)((p)[3]) << 24)   )

struct salsa20_ctx
{
    u32 input[16];
};

static void salsa20_wordtobyte(u8 output[64], const u32 input[16])
{
    u32 x[16];
    int i;

    memcpy(x, input, sizeof(x));
    for (i = 20; i > 0; i -= 2) {
        x[ 4] ^= rol32((x[ 0] + x[12]),  7);
        x[ 8] ^= rol32((x[ 4] + x[ 0]),  9);
        x[12] ^= rol32((x[ 8] + x[ 4]), 13);
        x[ 0] ^= rol32((x[12] + x[ 8]), 18);
        x[ 9] ^= rol32((x[ 5] + x[ 1]),  7);
        x[13] ^= rol32((x[ 9] + x[ 5]),  9);
        x[ 1] ^= rol32((x[13] + x[ 9]), 13);
        x[ 5] ^= rol32((x[ 1] + x[13]), 18);
        x[14] ^= rol32((x[10] + x[ 6]),  7);
        x[ 2] ^= rol32((x[14] + x[10]),  9);
        x[ 6] ^= rol32((x[ 2] + x[14]), 13);
        x[10] ^= rol32((x[ 6] + x[ 2]), 18);
        x[ 3] ^= rol32((x[15] + x[11]),  7);
        x[ 7] ^= rol32((x[ 3] + x[15]),  9);
        x[11] ^= rol32((x[ 7] + x[ 3]), 13);
        x[15] ^= rol32((x[11] + x[ 7]), 18);
        x[ 1] ^= rol32((x[ 0] + x[ 3]),  7);
        x[ 2] ^= rol32((x[ 1] + x[ 0]),  9);
        x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
        x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
        x[ 6] ^= rol32((x[ 5] + x[ 4]),  7);
        x[ 7] ^= rol32((x[ 6] + x[ 5]),  9);
        x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
        x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
        x[11] ^= rol32((x[10] + x[ 9]),  7);
        x[ 8] ^= rol32((x[11] + x[10]),  9);
        x[ 9] ^= rol32((x[ 8] + x[11]), 13);
        x[10] ^= rol32((x[ 9] + x[ 8]), 18);
        x[12] ^= rol32((x[15] + x[14]),  7);
        x[13] ^= rol32((x[12] + x[15]),  9);
        x[14] ^= rol32((x[13] + x[12]), 13);
        x[15] ^= rol32((x[14] + x[13]), 18);
    }
    for (i = 0; i < 16; ++i)
        x[i] += input[i];
    for (i = 0; i < 16; ++i)
        U32TO8_LITTLE(output + 4 * i,x[i]);
}

static const char sigma[16] = "expand 32-byte k";
static const char tau[16] = "expand 16-byte k";

static void salsa20_keysetup(struct salsa20_ctx *ctx, const u8 *k, u32 kbytes)
{
    const char *constants;

    ctx->input[1] = U8TO32_LITTLE(k + 0);
    ctx->input[2] = U8TO32_LITTLE(k + 4);
    ctx->input[3] = U8TO32_LITTLE(k + 8);
    ctx->input[4] = U8TO32_LITTLE(k + 12);
    if (kbytes == 32) { /* recommended */
        k += 16;
        constants = sigma;
    } else { /* kbytes == 16 */
        constants = tau;
    }
    ctx->input[11] = U8TO32_LITTLE(k + 0);
    ctx->input[12] = U8TO32_LITTLE(k + 4);
    ctx->input[13] = U8TO32_LITTLE(k + 8);
    ctx->input[14] = U8TO32_LITTLE(k + 12);
    ctx->input[0] = U8TO32_LITTLE(constants + 0);
    ctx->input[5] = U8TO32_LITTLE(constants + 4);
    ctx->input[10] = U8TO32_LITTLE(constants + 8);
    ctx->input[15] = U8TO32_LITTLE(constants + 12);
}

static void salsa20_ivsetup(struct salsa20_ctx *ctx, const u8 *iv)
{
    ctx->input[6] = U8TO32_LITTLE(iv + 0);
    ctx->input[7] = U8TO32_LITTLE(iv + 4);
    ctx->input[8] = 0;
    ctx->input[9] = 0;
}

static void salsa20_encrypt_bytes(struct salsa20_ctx *ctx, u8 *dst,
                  const u8 *src, unsigned int bytes)
{
    u8 buf[64];

    if (dst != src)
        memcpy(dst, src, bytes);

    while (bytes) {
        salsa20_wordtobyte(buf, ctx->input);

        ctx->input[8]++;
        if (!ctx->input[8])
            ctx->input[9]++;

        if (bytes <= 64) {
            crypto_xor(dst, buf, bytes);
            return;
        }

        crypto_xor(dst, buf, 64);
        bytes -= 64;
        dst += 64;
    }
}

/*
 * End of code taken from D. J. Bernstein's reference implementation.
 */

static int setkey(struct crypto_tfm *tfm, const u8 *key,
          unsigned int keysize)
{
    struct salsa20_ctx *ctx = crypto_tfm_ctx(tfm);
    salsa20_keysetup(ctx, key, keysize);
    return 0;
}

static int encrypt(struct blkcipher_desc *desc,
           struct scatterlist *dst, struct scatterlist *src,
           unsigned int nbytes)
{
    struct blkcipher_walk walk;
    struct crypto_blkcipher *tfm = desc->tfm;
    struct salsa20_ctx *ctx = crypto_blkcipher_ctx(tfm);
    int err;

    blkcipher_walk_init(&walk, dst, src, nbytes);
    err = blkcipher_walk_virt_block(desc, &walk, 64);

    salsa20_ivsetup(ctx, walk.iv);

    if (likely(walk.nbytes == nbytes))
    {
        salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
                      walk.src.virt.addr, nbytes);
        return blkcipher_walk_done(desc, &walk, 0);
    }

    while (walk.nbytes >= 64) {
        salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
                      walk.src.virt.addr,
                      walk.nbytes - (walk.nbytes % 64));
        err = blkcipher_walk_done(desc, &walk, walk.nbytes % 64);
    }

    if (walk.nbytes) {
        salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
                      walk.src.virt.addr, walk.nbytes);
        err = blkcipher_walk_done(desc, &walk, 0);
    }

    return err;
}

static struct crypto_alg alg = {
    .cra_name           =   "salsa20",
    .cra_driver_name    =   "salsa20-generic",
    .cra_priority       =   100,
    .cra_flags          =   CRYPTO_ALG_TYPE_BLKCIPHER,
    .cra_type           =   &crypto_blkcipher_type,
    .cra_blocksize      =   1,
    .cra_ctxsize        =   sizeof(struct salsa20_ctx),
    .cra_alignmask      =   3,
    .cra_module         =   THIS_MODULE,
    .cra_u              =   {
        .blkcipher = {
            .setkey         =   setkey,
            .encrypt        =   encrypt,
            .decrypt        =   encrypt,
            .min_keysize    =   SALSA20_MIN_KEY_SIZE,
            .max_keysize    =   SALSA20_MAX_KEY_SIZE,
            .ivsize         =   SALSA20_IV_SIZE,
        }
    }
};

static int __init salsa20_generic_mod_init(void)
{
    return crypto_register_alg(&alg);
}

static void __exit salsa20_generic_mod_fini(void)
{
    crypto_unregister_alg(&alg);
}

module_init(salsa20_generic_mod_init);
module_exit(salsa20_generic_mod_fini);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
MODULE_ALIAS("salsa20");