git.distorted.org.uk Git - u/mdw/catacomb/blob - square-mktab.c

   1 /* -*-c-*-
   2  *
   3  * $Id: square-mktab.c,v 1.3 2004/04/08 01:36:15 mdw Exp $
   4  *
   5  * Build precomputed tables for the Square block cipher
   6  *
   7  * (c) 2000 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Header files ------------------------------------------------------*/
  31
  32 #include <assert.h>
  33 #include <stdio.h>
  34 #include <stdlib.h>
  35
  36 #include <mLib/bits.h>
  37
  38 /*----- Magic variables ---------------------------------------------------*/
  39
  40 static octet s[256], si[256];
  41 static uint32 t[4][256], ti[4][256];
  42 static uint32 u[4][256];
  43 static octet rc[32];
  44
  45 /*----- Main code ---------------------------------------------------------*/
  46
  47 /* --- @mul@ --- *
  48  *
  49  * Arguments:   @unsigned x, y@ = polynomials over %$\gf{2^8}$%
  50  *              @unsigned m@ = modulus
  51  *
  52  * Returns:     The product of two polynomials.
  53  *
  54  * Use:         Computes a product of polynomials, quite slowly.
  55  */
  56
  57 static unsigned mul(unsigned x, unsigned y, unsigned m)
  58 {
  59   unsigned a = 0;
  60   unsigned i;
  61
  62   for (i = 0; i < 8; i++) {
  63     if (y & 1)
  64       a ^= x;
  65     y >>= 1;
  66     x <<= 1;
  67     if (x & 0x100)
  68       x ^= m;
  69   }
  70
  71   return (a);
  72 }
  73
  74 /* --- @sbox@ --- *
  75  *
  76  * Build the S-box.
  77  *
  78  * This is built from inversion in the multiplicative group of
  79  * %$\gf{2^8}[x]/(p(x))$%, where %$p(x) = x^8+x^7+x^6+x^5+x^4+x^2+1$%,
  80  * followed by an affine transformation treating inputs as vectors over
  81  * %$\gf{2}$%.  The result is a horrible function.
  82  *
  83  * The inversion is done slightly sneakily, by building log and antilog
  84  * tables.  Let %$a$% be an element of the finite field.  If the inverse of
  85  * %$a$% is %$a^{-1}$%, then %$\log a a^{-1} = 0$%.  Hence
  86  * %$\log a = -\log a^{-1}$%.  This saves fiddling about with Euclidean
  87  * algorithm.
  88  */
  89
  90 #define S_MOD 0x1f5
  91
  92 static void sbox(void)
  93 {
  94   octet log[256], alog[256];
  95   unsigned x;
  96   unsigned i;
  97   unsigned g;
  98
  99   /* --- Find a suitable generator, and build log tables --- */
 100
 101   log[0] = 0;
 102   for (g = 2; g < 256; g++) {
 103     x = 1;
 104     for (i = 0; i < 256; i++) {
 105       log[x] = i;
 106       alog[i] = x;
 107       x = mul(x, g, S_MOD);
 108       if (x == 1 && i != 254)
 109         goto again;
 110     }
 111     goto done;
 112   again:;
 113   }
 114   fprintf(stderr, "couldn't find generator\n");
 115   exit(EXIT_FAILURE);
 116 done:;
 117
 118   /* --- Now grind through and do the affine transform --- *
 119    *
 120    * The matrix multiply is an AND and a parity op.  The add is an XOR.
 121    */
 122
 123   for (i = 0; i < 256; i++) {
 124     unsigned j;
 125     octet m[] = { 0xd6, 0x7b, 0x3d, 0x1f, 0x0f, 0x05, 0x03, 0x01 };
 126     unsigned v = i ? alog[255 - log[i]] : 0;
 127
 128     assert(i == 0 || mul(i, v, S_MOD) == 1);
 129
 130     x = 0;
 131     for (j = 0; j < 8; j++) {
 132       unsigned r;
 133       r = v & m[j];
 134       r = (r >> 4) ^ r;
 135       r = (r >> 2) ^ r;
 136       r = (r >> 1) ^ r;
 137       x = (x << 1) | (r & 1);
 138     }
 139     x ^= 0xb1;
 140     s[i] = x;
 141     si[x] = i;
 142   }
 143 }
 144
 145 /* --- @tbox@ --- *
 146  *
 147  * Construct the t tables for doing the round function efficiently.
 148  */
 149
 150 static void tbox(void)
 151 {
 152   unsigned i;
 153
 154   for (i = 0; i < 256; i++) {
 155     uint32 a, b, c, d;
 156     uint32 w;
 157
 158     /* --- Build a forwards t-box entry --- */
 159
 160     a = s[i];
 161     b = a << 1; if (b & 0x100) b ^= S_MOD;
 162     c = a ^ b;
 163     w = (b << 0) | (a << 8) | (a << 16) | (c << 24);
 164     t[0][i] = w;
 165     t[1][i] = ROL32(w, 8);
 166     t[2][i] = ROL32(w, 16);
 167     t[3][i] = ROL32(w, 24);
 168
 169     /* --- Build a backwards t-box entry --- */
 170
 171     a = mul(si[i], 0x0e, S_MOD);
 172     b = mul(si[i], 0x09, S_MOD);
 173     c = mul(si[i], 0x0d, S_MOD);
 174     d = mul(si[i], 0x0b, S_MOD);
 175     w = (a << 0) | (b << 8) | (c << 16) | (d << 24);
 176     ti[0][i] = w;
 177     ti[1][i] = ROL32(w, 8);
 178     ti[2][i] = ROL32(w, 16);
 179     ti[3][i] = ROL32(w, 24);
 180   }
 181 }
 182
 183 /* --- @ubox@ --- *
 184  *
 185  * Construct the tables for performing the key schedule.
 186  */
 187
 188 static void ubox(void)
 189 {
 190   unsigned i;
 191
 192   for (i = 0; i < 256; i++) {
 193     uint32 a, b, c;
 194     uint32 w;
 195     a = i;
 196     b = a << 1; if (b & 0x100) b ^= S_MOD;
 197     c = a ^ b;
 198     w = (b << 0) | (a << 8) | (a << 16) | (c << 24);
 199     u[0][i] = w;
 200     u[1][i] = ROL32(w, 8);
 201     u[2][i] = ROL32(w, 16);
 202     u[3][i] = ROL32(w, 24);
 203   }
 204 }
 205
 206 /* --- Round constants --- */
 207
 208 void rcon(void)
 209 {
 210   unsigned r = 1;
 211   int i;
 212
 213   for (i = 0; i < sizeof(rc); i++) {
 214     rc[i] = r;
 215     r <<= 1;
 216     if (r & 0x100)
 217       r ^= S_MOD;
 218   }
 219 }
 220
 221 /* --- @main@ --- */
 222
 223 int main(void)
 224 {
 225   int i, j;
 226
 227   puts("\
 228 /* -*-c-*-\n\
 229  *\n\
 230  * Square tables [generated]\n\
 231  */\n\
 232 \n\
 233 #ifndef CATACOMB_SQUARE_TAB_H\n\
 234 #define CATACOMB_SQUARE_TAB_H\n\
 235 ");
 236
 237   /* --- Write out the S-box --- */
 238
 239   sbox();
 240   fputs("\
 241 /* --- The byte substitution and its inverse --- */\n\
 242 \n\
 243 #define SQUARE_S {                                                      \\\n\
 244   ", stdout);
 245   for (i = 0; i < 256; i++) {
 246     printf("0x%02x", s[i]);
 247     if (i == 255)
 248       fputs("                   \\\n}\n\n", stdout);
 249     else if (i % 8 == 7)
 250       fputs(",                  \\\n  ", stdout);
 251     else
 252       fputs(", ", stdout);
 253   }
 254
 255   fputs("\
 256 #define SQUARE_SI {                                                     \\\n\
 257   ", stdout);
 258   for (i = 0; i < 256; i++) {
 259     printf("0x%02x", si[i]);
 260     if (i == 255)
 261       fputs("                   \\\n}\n\n", stdout);
 262     else if (i % 8 == 7)
 263       fputs(",                  \\\n  ", stdout);
 264     else
 265       fputs(", ", stdout);
 266   }
 267
 268   /* --- Write out the big t tables --- */
 269
 270   tbox();
 271   fputs("\
 272 /* --- The big round tables --- */\n\
 273 \n\
 274 #define SQUARE_T {                                                      \\\n\
 275   { ", stdout);
 276   for (j = 0; j < 4; j++) {
 277     for (i = 0; i < 256; i++) {
 278       printf("0x%08x", t[j][i]);
 279       if (i == 255) {
 280         if (j == 3)
 281           fputs(" }                     \\\n}\n\n", stdout);
 282         else
 283           fputs(" },                    \\\n\
 284                                                                         \\\n\
 285   { ", stdout);
 286       } else if (i % 4 == 3)
 287         fputs(",                        \\\n    ", stdout);
 288       else
 289         fputs(", ", stdout);
 290     }
 291   }
 292
 293   fputs("\
 294 #define SQUARE_TI {                                                     \\\n\
 295   { ", stdout);
 296   for (j = 0; j < 4; j++) {
 297     for (i = 0; i < 256; i++) {
 298       printf("0x%08x", ti[j][i]);
 299       if (i == 255) {
 300         if (j == 3)
 301           fputs(" }                     \\\n}\n\n", stdout);
 302         else
 303           fputs(" },                    \\\n\
 304                                                                         \\\n\
 305   { ", stdout);
 306       } else if (i % 4 == 3)
 307         fputs(",                        \\\n    ", stdout);
 308       else
 309         fputs(", ", stdout);
 310     }
 311   }
 312
 313   /* --- Write out the big u tables --- */
 314
 315   ubox();
 316   fputs("\
 317 /* --- The key schedule tables --- */\n\
 318 \n\
 319 #define SQUARE_U {                                                      \\\n\
 320   { ", stdout);
 321   for (j = 0; j < 4; j++) {
 322     for (i = 0; i < 256; i++) {
 323       printf("0x%08x", u[j][i]);
 324       if (i == 255) {
 325         if (j == 3)
 326           fputs(" }                     \\\n}\n\n", stdout);
 327         else
 328           fputs(" },                    \\\n\
 329                                                                         \\\n\
 330   { ", stdout);
 331       } else if (i % 4 == 3)
 332         fputs(",                        \\\n    ", stdout);
 333       else
 334         fputs(", ", stdout);
 335     }
 336   }
 337
 338   /* --- Round constants --- */
 339
 340   rcon();
 341   fputs("\
 342 /* --- The round constants --- */\n\
 343 \n\
 344 #define SQUARE_RCON {                                                   \\\n\
 345   ", stdout);
 346   for (i = 0; i < sizeof(rc); i++) {
 347     printf("0x%02x", rc[i]);
 348     if (i == sizeof(rc) - 1)
 349       fputs("                   \\\n}\n\n", stdout);
 350     else if (i % 8 == 7)
 351       fputs(",                  \\\n  ", stdout);
 352     else
 353       fputs(", ", stdout);
 354   }
 355
 356   /* --- Done --- */
 357
 358   puts("#endif");
 359
 360   if (fclose(stdout)) {
 361     fprintf(stderr, "error writing data\n");
 362     exit(EXIT_FAILURE);
 363   }
 364
 365   return (0);
 366 }
 367
 368 /*----- That's all, folks -------------------------------------------------*/