FreeBSD/Linux Kernel Cross Reference
sys/crypto/twofish.c

     /*
      * Twofish for CryptoAPI
      *
      * Originally Twofish for GPG
      * By Matthew Skala <mskala@ansuz.sooke.bc.ca>, 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 <Marc@Mutz.com>
      * Ported to CryptoAPI by Colin Slater <hoho@tacomeat.net>
     *
     * 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_list           =   LIST_HEAD_INIT(alg.cra_list),
           .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");

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