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

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