path: root/twofish.c

/* twofish.c
 *
 * The twofish block cipher.
 */

/* twofish - An implementation of the twofish cipher.
 * Copyright (C) 1999 Ruud de Rooij <ruud@debian.org>
 *
 * Modifications for lsh, integrated testing
 * Copyright (C) 1999 J.H.M. Dassen (Ray) <jdassen@wi.LeidenUniv.nl>
 *
 * Integrated with the nettle library,
 * Copyright (C) 2001 Niels Möller
 */

/* nettle, low-level cryptographics library
 *
 * The nettle library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 * 
 * The nettle Library 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 Lesser General Public
 * License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with the nettle library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02111-1301, USA.
 */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>
#include <string.h>

#include "twofish.h"

#include "macros.h"

/* Bitwise rotations on 32-bit words.  These are defined as macros that
 * evaluate their argument twice, so do not apply to any expressions with
 * side effects.
 */

#define rol1(x) (((x) << 1) | (((x) & 0x80000000) >> 31))
#define rol8(x) (((x) << 8) | (((x) & 0xFF000000) >> 24))
#define rol9(x) (((x) << 9) | (((x) & 0xFF800000) >> 23))
#define ror1(x) (((x) >> 1) | (((x) & 0x00000001) << 31))

/* ------------------------------------------------------------------------- */

/* The permutations q0 and q1.  These are fixed permutations on 8-bit values.
 * The permutations have been computed using the program twofish-data,
 * which is distributed along with this file.
 */

static const uint8_t q0[256] = {
  0xA9,0x67,0xB3,0xE8,0x04,0xFD,0xA3,0x76,
  0x9A,0x92,0x80,0x78,0xE4,0xDD,0xD1,0x38,
  0x0D,0xC6,0x35,0x98,0x18,0xF7,0xEC,0x6C,
  0x43,0x75,0x37,0x26,0xFA,0x13,0x94,0x48,
  0xF2,0xD0,0x8B,0x30,0x84,0x54,0xDF,0x23,
  0x19,0x5B,0x3D,0x59,0xF3,0xAE,0xA2,0x82,
  0x63,0x01,0x83,0x2E,0xD9,0x51,0x9B,0x7C,
  0xA6,0xEB,0xA5,0xBE,0x16,0x0C,0xE3,0x61,
  0xC0,0x8C,0x3A,0xF5,0x73,0x2C,0x25,0x0B,
  0xBB,0x4E,0x89,0x6B,0x53,0x6A,0xB4,0xF1,
  0xE1,0xE6,0xBD,0x45,0xE2,0xF4,0xB6,0x66,
  0xCC,0x95,0x03,0x56,0xD4,0x1C,0x1E,0xD7,
  0xFB,0xC3,0x8E,0xB5,0xE9,0xCF,0xBF,0xBA,
  0xEA,0x77,0x39,0xAF,0x33,0xC9,0x62,0x71,
  0x81,0x79,0x09,0xAD,0x24,0xCD,0xF9,0xD8,
  0xE5,0xC5,0xB9,0x4D,0x44,0x08,0x86,0xE7,
  0xA1,0x1D,0xAA,0xED,0x06,0x70,0xB2,0xD2,
  0x41,0x7B,0xA0,0x11,0x31,0xC2,0x27,0x90,
  0x20,0xF6,0x60,0xFF,0x96,0x5C,0xB1,0xAB,
  0x9E,0x9C,0x52,0x1B,0x5F,0x93,0x0A,0xEF,
  0x91,0x85,0x49,0xEE,0x2D,0x4F,0x8F,0x3B,
  0x47,0x87,0x6D,0x46,0xD6,0x3E,0x69,0x64,
  0x2A,0xCE,0xCB,0x2F,0xFC,0x97,0x05,0x7A,
  0xAC,0x7F,0xD5,0x1A,0x4B,0x0E,0xA7,0x5A,
  0x28,0x14,0x3F,0x29,0x88,0x3C,0x4C,0x02,
  0xB8,0xDA,0xB0,0x17,0x55,0x1F,0x8A,0x7D,
  0x57,0xC7,0x8D,0x74,0xB7,0xC4,0x9F,0x72,
  0x7E,0x15,0x22,0x12,0x58,0x07,0x99,0x34,
  0x6E,0x50,0xDE,0x68,0x65,0xBC,0xDB,0xF8,
  0xC8,0xA8,0x2B,0x40,0xDC,0xFE,0x32,0xA4,
  0xCA,0x10,0x21,0xF0,0xD3,0x5D,0x0F,0x00,
  0x6F,0x9D,0x36,0x42,0x4A,0x5E,0xC1,0xE0,
};

static const uint8_t q1[256] = {
  0x75,0xF3,0xC6,0xF4,0xDB,0x7B,0xFB,0xC8,
  0x4A,0xD3,0xE6,0x6B,0x45,0x7D,0xE8,0x4B,
  0xD6,0x32,0xD8,0xFD,0x37,0x71,0xF1,0xE1,
  0x30,0x0F,0xF8,0x1B,0x87,0xFA,0x06,0x3F,
  0x5E,0xBA,0xAE,0x5B,0x8A,0x00,0xBC,0x9D,
  0x6D,0xC1,0xB1,0x0E,0x80,0x5D,0xD2,0xD5,
  0xA0,0x84,0x07,0x14,0xB5,0x90,0x2C,0xA3,
  0xB2,0x73,0x4C,0x54,0x92,0x74,0x36,0x51,
  0x38,0xB0,0xBD,0x5A,0xFC,0x60,0x62,0x96,
  0x6C,0x42,0xF7,0x10,0x7C,0x28,0x27,0x8C,
  0x13,0x95,0x9C,0xC7,0x24,0x46,0x3B,0x70,
  0xCA,0xE3,0x85,0xCB,0x11,0xD0,0x93,0xB8,
  0xA6,0x83,0x20,0xFF,0x9F,0x77,0xC3,0xCC,
  0x03,0x6F,0x08,0xBF,0x40,0xE7,0x2B,0xE2,
  0x79,0x0C,0xAA,0x82,0x41,0x3A,0xEA,0xB9,
  0xE4,0x9A,0xA4,0x97,0x7E,0xDA,0x7A,0x17,
  0x66,0x94,0xA1,0x1D,0x3D,0xF0,0xDE,0xB3,
  0x0B,0x72,0xA7,0x1C,0xEF,0xD1,0x53,0x3E,
  0x8F,0x33,0x26,0x5F,0xEC,0x76,0x2A,0x49,
  0x81,0x88,0xEE,0x21,0xC4,0x1A,0xEB,0xD9,
  0xC5,0x39,0x99,0xCD,0xAD,0x31,0x8B,0x01,
  0x18,0x23,0xDD,0x1F,0x4E,0x2D,0xF9,0x48,
  0x4F,0xF2,0x65,0x8E,0x78,0x5C,0x58,0x19,
  0x8D,0xE5,0x98,0x57,0x67,0x7F,0x05,0x64,
  0xAF,0x63,0xB6,0xFE,0xF5,0xB7,0x3C,0xA5,
  0xCE,0xE9,0x68,0x44,0xE0,0x4D,0x43,0x69,
  0x29,0x2E,0xAC,0x15,0x59,0xA8,0x0A,0x9E,
  0x6E,0x47,0xDF,0x34,0x35,0x6A,0xCF,0xDC,
  0x22,0xC9,0xC0,0x9B,0x89,0xD4,0xED,0xAB,
  0x12,0xA2,0x0D,0x52,0xBB,0x02,0x2F,0xA9,
  0xD7,0x61,0x1E,0xB4,0x50,0x04,0xF6,0xC2,
  0x16,0x25,0x86,0x56,0x55,0x09,0xBE,0x91,
};

/* ------------------------------------------------------------------------- */

/* uint8_t gf_multiply(uint8_t p, uint8_t a, uint8_t b)
 *
 * Multiplication in GF(2^8).
 *
 * This function multiplies a times b in the Galois Field GF(2^8) with
 * primitive polynomial p.
 * The representation of the polynomials a, b, and p uses bits with
 * values 2^i to represent the terms x^i.  The polynomial p contains an
 * implicit term x^8.
 *
 * Note that addition and subtraction in GF(2^8) is simply the XOR
 * operation.
 */

static uint8_t
gf_multiply(uint8_t p, uint8_t a, uint8_t b)
{
  uint32_t shift  = b;
  uint8_t result = 0;
  while (a)
    {
      if (a & 1) result ^= shift;
      a = a >> 1;
      shift = shift << 1;
      if (shift & 0x100) shift ^= p;
    }
  return result;
}

/* ------------------------------------------------------------------------- */

/* The matrix RS as specified in section 4.3 the twofish paper. */

static const uint8_t rs_matrix[4][8] = {
    { 0x01, 0xA4, 0x55, 0x87, 0x5A, 0x58, 0xDB, 0x9E },
    { 0xA4, 0x56, 0x82, 0xF3, 0x1E, 0xC6, 0x68, 0xE5 },
    { 0x02, 0xA1, 0xFC, 0xC1, 0x47, 0xAE, 0x3D, 0x19 },
    { 0xA4, 0x55, 0x87, 0x5A, 0x58, 0xDB, 0x9E, 0x03 } };

/* uint32_t compute_s(uint32_t m1, uint32_t m2);
 *
 * Computes the value RS * M, where M is a byte vector composed of the
 * bytes of m1 and m2.  Arithmetic is done in GF(2^8) with primitive
 * polynomial x^8 + x^6 + x^3 + x^2 + 1.
 *
 * This function is used to compute the sub-keys S which are in turn used
 * to generate the S-boxes.
 */

static uint32_t
compute_s(uint32_t m1, uint32_t m2)
{
  uint32_t s = 0;
  int i;
  for (i = 0; i < 4; i++)
    s |=  ((  gf_multiply(0x4D, m1,       rs_matrix[i][0])
	    ^ gf_multiply(0x4D, m1 >> 8,  rs_matrix[i][1])
	    ^ gf_multiply(0x4D, m1 >> 16, rs_matrix[i][2])
	    ^ gf_multiply(0x4D, m1 >> 24, rs_matrix[i][3])
	    ^ gf_multiply(0x4D, m2,       rs_matrix[i][4])
	    ^ gf_multiply(0x4D, m2 >> 8,  rs_matrix[i][5])
	    ^ gf_multiply(0x4D, m2 >> 16, rs_matrix[i][6])
	    ^ gf_multiply(0x4D, m2 >> 24, rs_matrix[i][7])) << (i*8));
  return s;
}

/* ------------------------------------------------------------------------- */

/* This table describes which q S-boxes are used for each byte in each stage
 * of the function h, cf. figure 2 of the twofish paper.
 */

static const uint8_t * const q_table[4][5] =
  { { q1, q1, q0, q0, q1 },
    { q0, q1, q1, q0, q0 },
    { q0, q0, q0, q1, q1 },
    { q1, q0, q1, q1, q0 } };

/* The matrix MDS as specified in section 4.3.2 of the twofish paper. */

static const uint8_t mds_matrix[4][4] = { { 0x01, 0xEF, 0x5B, 0x5B },
				 { 0x5B, 0xEF, 0xEF, 0x01 },
				 { 0xEF, 0x5B, 0x01, 0xEF },
				 { 0xEF, 0x01, 0xEF, 0x5B } };

/* uint32_t h_uint8_t(int k, int i, uint8_t x, uint8_t l0, uint8_t l1, uint8_t l2, uint8_t l3);
 *
 * Perform the h function (section 4.3.2) on one byte.  It consists of
 * repeated applications of the q permutation, followed by a XOR with
 * part of a sub-key.  Finally, the value is multiplied by one column of
 * the MDS matrix.  To obtain the result for a full word, the results of
 * h for the individual bytes are XORed.
 *
 * k is the key size (/ 64 bits), i is the byte number (0 = LSB), x is the
 * actual byte to apply the function to; l0, l1, l2, and l3 are the
 * appropriate bytes from the subkey.  Note that only l0..l(k-1) are used.
 */

static uint32_t
h_byte(int k, int i, uint8_t x, uint8_t l0, uint8_t l1, uint8_t l2, uint8_t l3)
{
  uint8_t y = q_table[i][4][l0 ^
            q_table[i][3][l1 ^
              q_table[i][2][k == 2 ? x : l2 ^
                q_table[i][1][k == 3 ? x : l3 ^ q_table[i][0][x]]]]];

  return ( ((uint32_t)gf_multiply(0x69, mds_matrix[0][i], y))
	   | ((uint32_t)gf_multiply(0x69, mds_matrix[1][i], y) << 8)
	   | ((uint32_t)gf_multiply(0x69, mds_matrix[2][i], y) << 16)
	   | ((uint32_t)gf_multiply(0x69, mds_matrix[3][i], y) << 24) );
}

/* uint32_t h(int k, uint8_t x, uint32_t l0, uint32_t l1, uint32_t l2, uint32_t l3);
 *
 * Perform the function h on a word.  See the description of h_byte() above.
 */

static uint32_t
h(int k, uint8_t x, uint32_t l0, uint32_t l1, uint32_t l2, uint32_t l3)
{
  return (  h_byte(k, 0, x, l0,       l1,       l2,       l3)
	  ^ h_byte(k, 1, x, l0 >> 8,  l1 >> 8,  l2 >> 8,  l3 >> 8)
	  ^ h_byte(k, 2, x, l0 >> 16, l1 >> 16, l2 >> 16, l3 >> 16)
	  ^ h_byte(k, 3, x, l0 >> 24, l1 >> 24, l2 >> 24, l3 >> 24) );
}


/* ------------------------------------------------------------------------- */

/* API */

/* Structure which contains the tables containing the subkeys and the
 * key-dependent s-boxes.
 */


/* Set up internal tables required for twofish encryption and decryption.
 *
 * The key size is specified in bytes.  Key sizes up to 32 bytes are
 * supported.  Larger key sizes are silently truncated.  
 */

void
twofish_set_key(struct twofish_ctx *context,
		size_t keysize, const uint8_t *key)
{
  uint8_t key_copy[32];
  uint32_t m[8], s[4], t;
  int i, j, k;

  /* Extend key as necessary */

  assert(keysize <= 32);

  /* We do a little more copying than necessary, but that doesn't
   * really matter. */
  memset(key_copy, 0, 32);
  memcpy(key_copy, key, keysize);

  for (i = 0; i<8; i++)
    m[i] = LE_READ_UINT32(key_copy + i*4);
  
  if (keysize <= 16)
    k = 2;
  else if (keysize <= 24)
    k = 3;
  else
    k = 4;

  /* Compute sub-keys */

  for (i = 0; i < 20; i++)
    {
      t = h(k, 2*i+1, m[1], m[3], m[5], m[7]);
      t = rol8(t);
      t += (context->keys[2*i] =
	    t + h(k, 2*i, m[0], m[2], m[4], m[6]));
      t = rol9(t);
      context->keys[2*i+1] = t;
    }

  /* Compute key-dependent S-boxes */

  for (i = 0; i < k; i++)
    s[k-1-i] = compute_s(m[2*i], m[2*i+1]);

  for (i = 0; i < 4; i++)
    for (j = 0; j < 256; j++)
      context->s_box[i][j] = h_byte(k, i, j,
				    s[0] >> (i*8),
				    s[1] >> (i*8),
				    s[2] >> (i*8),
				    s[3] >> (i*8));
}

/* Encrypt blocks of 16 bytes of data with the twofish algorithm.
 *
 * Before this function can be used, twofish_set_key() must be used in order to
 * set up various tables required for the encryption algorithm.
 * 
 * This function always encrypts 16 bytes of plaintext to 16 bytes of
 * ciphertext.  The memory areas of the plaintext and the ciphertext can
 * overlap.
 */

void
twofish_encrypt(const struct twofish_ctx *context,
		size_t length,
		uint8_t *ciphertext,
		const uint8_t *plaintext)
{
  const uint32_t * keys        = context->keys;
  const uint32_t (*s_box)[256] = context->s_box;

  assert( !(length % TWOFISH_BLOCK_SIZE) );
  for ( ; length; length -= TWOFISH_BLOCK_SIZE)
    {  
      uint32_t words[4];
      uint32_t r0, r1, r2, r3, t0, t1;
      int i;

      for (i = 0; i<4; i++, plaintext += 4)
	words[i] = LE_READ_UINT32(plaintext);

      r0 = words[0] ^ keys[0];
      r1 = words[1] ^ keys[1];
      r2 = words[2] ^ keys[2];
      r3 = words[3] ^ keys[3];
  
      for (i = 0; i < 8; i++) {
	t1 = (  s_box[1][r1 & 0xFF]
		^ s_box[2][(r1 >> 8) & 0xFF]
		^ s_box[3][(r1 >> 16) & 0xFF]
		^ s_box[0][(r1 >> 24) & 0xFF]);
	t0 = (  s_box[0][r0 & 0xFF]
		^ s_box[1][(r0 >> 8) & 0xFF]
		^ s_box[2][(r0 >> 16) & 0xFF]
		^ s_box[3][(r0 >> 24) & 0xFF]) + t1;
	r3 = (t1 + t0 + keys[4*i+9]) ^ rol1(r3);
	r2 = (t0 + keys[4*i+8]) ^ r2;
	r2 = ror1(r2);

	t1 = (  s_box[1][r3 & 0xFF]
		^ s_box[2][(r3 >> 8) & 0xFF]
		^ s_box[3][(r3 >> 16) & 0xFF]
		^ s_box[0][(r3 >> 24) & 0xFF]);
	t0 = (  s_box[0][r2 & 0xFF]
		^ s_box[1][(r2 >> 8) & 0xFF]
		^ s_box[2][(r2 >> 16) & 0xFF]
		^ s_box[3][(r2 >> 24) & 0xFF]) + t1;
	r1 = (t1 + t0 + keys[4*i+11]) ^ rol1(r1);
	r0 = (t0 + keys[4*i+10]) ^ r0;
	r0 = ror1(r0);
      }

      words[0] = r2 ^ keys[4];
      words[1] = r3 ^ keys[5];
      words[2] = r0 ^ keys[6];
      words[3] = r1 ^ keys[7];

      for (i = 0; i<4; i++, ciphertext += 4)
	LE_WRITE_UINT32(ciphertext, words[i]);
    }
}

/* Decrypt blocks of 16 bytes of data with the twofish algorithm.
 *
 * Before this function can be used, twofish_set_key() must be used in order to
 * set up various tables required for the decryption algorithm.
 * 
 * This function always decrypts 16 bytes of ciphertext to 16 bytes of
 * plaintext.  The memory areas of the plaintext and the ciphertext can
 * overlap.
 */

void
twofish_decrypt(const struct twofish_ctx *context,
		size_t length,
		uint8_t *plaintext,
		const uint8_t *ciphertext)

{
  const uint32_t *keys  = context->keys;
  const uint32_t (*s_box)[256] = context->s_box;

  assert( !(length % TWOFISH_BLOCK_SIZE) );
  for ( ; length; length -= TWOFISH_BLOCK_SIZE)
    {  
      uint32_t words[4];
      uint32_t r0, r1, r2, r3, t0, t1;
      int i;

      for (i = 0; i<4; i++, ciphertext += 4)
	words[i] = LE_READ_UINT32(ciphertext);

      r0 = words[2] ^ keys[6];
      r1 = words[3] ^ keys[7];
      r2 = words[0] ^ keys[4];
      r3 = words[1] ^ keys[5];

      for (i = 0; i < 8; i++) {
	t1 = (  s_box[1][r3 & 0xFF]
		^ s_box[2][(r3 >> 8) & 0xFF]
		^ s_box[3][(r3 >> 16) & 0xFF]
		^ s_box[0][(r3 >> 24) & 0xFF]);
	t0 = (  s_box[0][r2 & 0xFF]
		^ s_box[1][(r2 >> 8) & 0xFF]
		^ s_box[2][(r2 >> 16) & 0xFF]
		^ s_box[3][(r2 >> 24) & 0xFF]) + t1;
	r1 = (t1 + t0 + keys[39-4*i]) ^ r1;
	r1 = ror1(r1);
	r0 = (t0 + keys[38-4*i]) ^ rol1(r0);

	t1 = (  s_box[1][r1 & 0xFF]
		^ s_box[2][(r1 >> 8) & 0xFF]
		^ s_box[3][(r1 >> 16) & 0xFF]
		^ s_box[0][(r1 >> 24) & 0xFF]);
	t0 = (  s_box[0][r0 & 0xFF]
		^ s_box[1][(r0 >> 8) & 0xFF]
		^ s_box[2][(r0 >> 16) & 0xFF]
		^ s_box[3][(r0 >> 24) & 0xFF]) + t1;
	r3 = (t1 + t0 + keys[37-4*i]) ^ r3;
	r3 = ror1(r3);
	r2 = (t0 + keys[36-4*i]) ^ rol1(r2);
      }

      words[0] = r0 ^ keys[0];
      words[1] = r1 ^ keys[1];
      words[2] = r2 ^ keys[2];
      words[3] = r3 ^ keys[3];

      for (i = 0; i<4; i++, plaintext += 4)
	LE_WRITE_UINT32(plaintext, words[i]);
    }
}