twofish_generic.c

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/*
 * Twofish for CryptoAPI
 *
 * Originally Twofish for GPG
 * By Matthew Skala <[email protected]>, July 26, 1998
 * 256-bit key length added March 20, 1999
 * Some modifications to reduce the text size by Werner Koch, April, 1998
 * Ported to the kerneli patch by Marc Mutz <[email protected]>
 * Ported to CryptoAPI by Colin Slater <[email protected]>
 *
 * The original author has disclaimed all copyright interest in this
 * code and thus put it in the public domain. The subsequent authors 
 * have put this under the GNU General Public License.
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
 * USA
 *
 * This code is a "clean room" implementation, written from the paper
 * _Twofish: A 128-Bit Block Cipher_ by Bruce Schneier, John Kelsey,
 * Doug Whiting, David Wagner, Chris Hall, and Niels Ferguson, available
 * through http://www.counterpane.com/twofish.html
 *
 * For background information on multiplication in finite fields, used for
 * the matrix operations in the key schedule, see the book _Contemporary
 * Abstract Algebra_ by Joseph A. Gallian, especially chapter 22 in the
 * Third Edition.
 */

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

/* Macros to compute the g() function in the encryption and decryption
 * rounds.  G1 is the straight g() function; G2 includes the 8-bit
 * rotation for the high 32-bit word. */

#define G1(a) \
     (ctx->s[0][(a) & 0xFF]) ^ (ctx->s[1][((a) >> 8) & 0xFF]) \
   ^ (ctx->s[2][((a) >> 16) & 0xFF]) ^ (ctx->s[3][(a) >> 24])

#define G2(b) \
     (ctx->s[1][(b) & 0xFF]) ^ (ctx->s[2][((b) >> 8) & 0xFF]) \
   ^ (ctx->s[3][((b) >> 16) & 0xFF]) ^ (ctx->s[0][(b) >> 24])

/* Encryption and decryption Feistel rounds.  Each one calls the two g()
 * macros, does the PHT, and performs the XOR and the appropriate bit
 * rotations.  The parameters are the round number (used to select subkeys),
 * and the four 32-bit chunks of the text. */

#define ENCROUND(n, a, b, c, d) \
   x = G1 (a); y = G2 (b); \
   x += y; y += x + ctx->k[2 * (n) + 1]; \
   (c) ^= x + ctx->k[2 * (n)]; \
   (c) = ror32((c), 1); \
   (d) = rol32((d), 1) ^ y

#define DECROUND(n, a, b, c, d) \
   x = G1 (a); y = G2 (b); \
   x += y; y += x; \
   (d) ^= y + ctx->k[2 * (n) + 1]; \
   (d) = ror32((d), 1); \
   (c) = rol32((c), 1); \
   (c) ^= (x + ctx->k[2 * (n)])

/* Encryption and decryption cycles; each one is simply two Feistel rounds
 * with the 32-bit chunks re-ordered to simulate the "swap" */

#define ENCCYCLE(n) \
   ENCROUND (2 * (n), a, b, c, d); \
   ENCROUND (2 * (n) + 1, c, d, a, b)

#define DECCYCLE(n) \
   DECROUND (2 * (n) + 1, c, d, a, b); \
   DECROUND (2 * (n), a, b, c, d)

/* Macros to convert the input and output bytes into 32-bit words,
 * and simultaneously perform the whitening step.  INPACK packs word
 * number n into the variable named by x, using whitening subkey number m.
 * OUTUNPACK unpacks word number n from the variable named by x, using
 * whitening subkey number m. */

#define INPACK(n, x, m) \
   x = le32_to_cpu(src[n]) ^ ctx->w[m]

#define OUTUNPACK(n, x, m) \
   x ^= ctx->w[m]; \
   dst[n] = cpu_to_le32(x)



/* Encrypt one block.  in and out may be the same. */
static void twofish_encrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
{
    struct twofish_ctx *ctx = crypto_tfm_ctx(tfm);
    const __le32 *src = (const __le32 *)in;
    __le32 *dst = (__le32 *)out;

    /* The four 32-bit chunks of the text. */
    u32 a, b, c, d;
    
    /* Temporaries used by the round function. */
    u32 x, y;

    /* Input whitening and packing. */
    INPACK (0, a, 0);
    INPACK (1, b, 1);
    INPACK (2, c, 2);
    INPACK (3, d, 3);
    
    /* Encryption Feistel cycles. */
    ENCCYCLE (0);
    ENCCYCLE (1);
    ENCCYCLE (2);
    ENCCYCLE (3);
    ENCCYCLE (4);
    ENCCYCLE (5);
    ENCCYCLE (6);
    ENCCYCLE (7);
    
    /* Output whitening and unpacking. */
    OUTUNPACK (0, c, 4);
    OUTUNPACK (1, d, 5);
    OUTUNPACK (2, a, 6);
    OUTUNPACK (3, b, 7);
    
}

/* Decrypt one block.  in and out may be the same. */
static void twofish_decrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
{
    struct twofish_ctx *ctx = crypto_tfm_ctx(tfm);
    const __le32 *src = (const __le32 *)in;
    __le32 *dst = (__le32 *)out;
  
    /* The four 32-bit chunks of the text. */
    u32 a, b, c, d;
    
    /* Temporaries used by the round function. */
    u32 x, y;
    
    /* Input whitening and packing. */
    INPACK (0, c, 4);
    INPACK (1, d, 5);
    INPACK (2, a, 6);
    INPACK (3, b, 7);
    
    /* Encryption Feistel cycles. */
    DECCYCLE (7);
    DECCYCLE (6);
    DECCYCLE (5);
    DECCYCLE (4);
    DECCYCLE (3);
    DECCYCLE (2);
    DECCYCLE (1);
    DECCYCLE (0);

    /* Output whitening and unpacking. */
    OUTUNPACK (0, a, 0);
    OUTUNPACK (1, b, 1);
    OUTUNPACK (2, c, 2);
    OUTUNPACK (3, d, 3);

}

static struct crypto_alg alg = {
    .cra_name           =   "twofish",
    .cra_driver_name    =   "twofish-generic",
    .cra_priority       =   100,
    .cra_flags          =   CRYPTO_ALG_TYPE_CIPHER,
    .cra_blocksize      =   TF_BLOCK_SIZE,
    .cra_ctxsize        =   sizeof(struct twofish_ctx),
    .cra_alignmask      =   3,
    .cra_module         =   THIS_MODULE,
    .cra_u              =   { .cipher = {
    .cia_min_keysize    =   TF_MIN_KEY_SIZE,
    .cia_max_keysize    =   TF_MAX_KEY_SIZE,
    .cia_setkey         =   twofish_setkey,
    .cia_encrypt        =   twofish_encrypt,
    .cia_decrypt        =   twofish_decrypt } }
};

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

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

module_init(twofish_mod_init);
module_exit(twofish_mod_fini);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION ("Twofish Cipher Algorithm");
MODULE_ALIAS("twofish");