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   1 /* -*-c-*-
   2  *
   3  * $Id: dsarand.c,v 1.2 2000/06/17 10:54:00 mdw Exp $
   4  *
   5  * Random number generator for DSA
   6  *
   7  * (c) 1999 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 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: dsarand.c,v $
  33  * Revision 1.2  2000/06/17 10:54:00  mdw
  34  * Typesetting fixes.  Arena support.
  35  *
  36  * Revision 1.1  1999/12/22 15:53:12  mdw
  37  * Random number generator for finding DSA parameters.
  38  *
  39  */
  40
  41 /*----- Header files ------------------------------------------------------*/
  42
  43 #include <stdarg.h>
  44 #include <string.h>
  45
  46 #include <mLib/alloc.h>
  47 #include <mLib/bits.h>
  48 #include <mLib/sub.h>
  49
  50 #include "dsarand.h"
  51 #include "grand.h"
  52 #include "sha.h"
  53
  54 /*----- Main code ---------------------------------------------------------*/
  55
  56 /* --- @STEP@ --- *
  57  *
  58  * Arguments:   @dsarand *d@ = pointer to context
  59  *
  60  * Use:         Increments the buffer by one, interpreting it as a big-endian
  61  *              integer.  Carries outside the integer are discarded.
  62  */
  63
  64 #define STEP(d) do {                                                    \
  65   dsarand *_d = (d);                                                    \
  66   octet *_p = _d->p;                                                    \
  67   octet *_q = _p + _d->sz;                                              \
  68   unsigned _c = 1;                                                      \
  69   while (_c && _q > _p) {                                               \
  70     _c += *--_q;                                                        \
  71     *_q = U8(_c);                                                       \
  72     _c >>= 8;                                                           \
  73   }                                                                     \
  74 } while (0)
  75
  76 /* --- @dsarand_init@ --- *
  77  *
  78  * Arguments:   @dsarand *d@ = pointer to context
  79  *              @const void *p@ = pointer to seed buffer
  80  *              @size_t sz@ = size of the buffer
  81  *
  82  * Returns:     ---
  83  *
  84  * Use:         Initializes a DSA random number generator.
  85  */
  86
  87 void dsarand_init(dsarand *d, const void *p, size_t sz)
  88 {
  89   d->p = xmalloc(sz);
  90   d->sz = sz;
  91   d->passes = 1;
  92   if (p)
  93     memcpy(d->p, p, sz);
  94 }
  95
  96 /* --- @dsarand_reseed@ --- *
  97  *
  98  * Arguments:   @dsarand *d@ = pointer to context
  99  *              @const void *p@ = pointer to seed buffer
 100  *              @size_t sz@ = size of the buffer
 101  *
 102  * Returns:     ---
 103  *
 104  * Use:         Initializes a DSA random number generator.
 105  */
 106
 107 void dsarand_reseed(dsarand *d, const void *p, size_t sz)
 108 {
 109   xfree(d->p);
 110   d->p = xmalloc(sz);
 111   d->sz = sz;
 112   d->passes = 1;
 113   if (p)
 114     memcpy(d->p, p, sz);
 115 }
 116
 117 /* --- @dsarand_destroy@ --- *
 118  *
 119  * Arguments:   @dsarand *d@ = pointer to context
 120  *
 121  * Returns:     ---
 122  *
 123  * Use:         Disposes of a DSA random number generation context.
 124  */
 125
 126 void dsarand_destroy(dsarand *d)
 127 {
 128   xfree(d->p);
 129 }
 130
 131 /* --- @dsarand_fill@ --- *
 132  *
 133  * Arguments:   @dsarand *d@ = pointer to context
 134  *              @void *p@ = pointer to output buffer
 135  *              @size_t sz@ = size of output buffer
 136  *
 137  * Returns:     ---
 138  *
 139  * Use:         Fills an output buffer with pseudorandom data.
 140  *
 141  *              Let %$p$% be the numerical value of the input buffer, and let
 142  *              %$b$% be the number of bytes required.  Let
 143  *              %$z = \lceil b / 20 \rceil$% be the number of SHA outputs
 144  *              required.  Then the output of pass %$n$% is
 145  *
 146  *                %$P_n = \sum_{0 \le i < z} 2^{160i} SHA(p + nz + i)$%
 147  *                                                      %${} \bmod 2^{8b}$%
 148  *
 149  *              and the actual result in the output buffer is the XOR of all
 150  *              of the output passes.
 151  *
 152  *              The DSA procedure for choosing @q@ involves two passes with
 153  *              %$z = 1$%; the procedure for choosing @p@ involves one pass
 154  *              with larger %$z$%.  This generalization of the DSA generation
 155  *              procedure is my own invention but it seems relatively sound.
 156  */
 157
 158 void dsarand_fill(dsarand *d, void *p, size_t sz)
 159 {
 160   octet *q = p;
 161   unsigned n = d->passes;
 162
 163   /* --- Write out the first pass --- *
 164    *
 165    * This can write directly to the output buffer, so it's done differently
 166    * from the latter passes.
 167    */
 168
 169   {
 170     size_t o = sz;
 171
 172     while (o) {
 173       sha_ctx h;
 174
 175       /* --- Hash the input buffer --- */
 176
 177       sha_init(&h);
 178       sha_hash(&h, d->p, d->sz);
 179
 180       /* --- If enough space, extract the hash output directly --- */
 181
 182       if (o >= SHA_HASHSZ) {
 183         o -= SHA_HASHSZ;
 184         sha_done(&h, q + o);
 185       }
 186
 187       /* --- Otherwise take the hash result out of line and copy it --- */
 188
 189       else {
 190         octet hash[SHA_HASHSZ];
 191         sha_done(&h, hash);
 192         memcpy(q, hash + (SHA_HASHSZ - o), o);
 193         o = 0;
 194       }
 195
 196       /* --- Step the input buffer --- */
 197
 198       STEP(d);
 199     }
 200
 201     /* --- Another pass has been done --- */
 202
 203     n--;
 204   }
 205
 206   /* --- Write out subsequent passes --- *
 207    *
 208    * The hash output has to be done offline, so this is slightly easier.
 209    */
 210
 211   while (n) {
 212     size_t o = sz;
 213
 214     while (o) {
 215       sha_ctx h;
 216       octet hash[SHA_HASHSZ];
 217       size_t n;
 218       octet *pp, *qq;
 219
 220       /* --- Hash the input buffer --- */
 221
 222       sha_init(&h);
 223       sha_hash(&h, d->p, d->sz);
 224       sha_done(&h, hash);
 225
 226       /* --- Work out how much output is wanted --- */
 227
 228       n = SHA_HASHSZ;
 229       if (n > o)
 230         n = o;
 231       o -= n;
 232
 233       /* --- XOR the data out --- */
 234
 235       for (pp = hash + (SHA_HASHSZ - n), qq = q + o;
 236            pp < hash + SHA_HASHSZ; pp++, qq++)
 237         *qq ^= *pp;
 238
 239       /* --- Step the input buffer --- */
 240
 241       STEP(d);
 242     }
 243
 244     /* --- Another pass is done --- */
 245
 246     n--;
 247   }
 248 }
 249
 250 /*----- Generic pseudorandom-number generator interface -------------------*/
 251
 252 static const grand_ops gops;
 253
 254 typedef struct gctx {
 255   grand r;
 256   dsarand d;
 257 } gctx;
 258
 259 static void gdestroy(grand *r)
 260 {
 261   gctx *g = (gctx *)r;
 262   dsarand_destroy(&g->d);
 263   DESTROY(g);
 264 }
 265
 266 static int gmisc(grand *r, unsigned op, ...)
 267 {
 268   gctx *g = (gctx *)r;
 269   va_list ap;
 270   int rc = 0;
 271   va_start(ap, op);
 272
 273   switch (op) {
 274     case GRAND_CHECK:
 275       switch (va_arg(ap, unsigned)) {
 276         case GRAND_CHECK:
 277         case GRAND_SEEDBLOCK:
 278         case GRAND_SEEDRAND:
 279         case DSARAND_PASSES:
 280           rc = 1;
 281           break;
 282         default:
 283           rc = 0;
 284           break;
 285       }
 286       break;
 287     case GRAND_SEEDBLOCK: {
 288       const void *p = va_arg(ap, const void *);
 289       size_t sz = va_arg(ap, size_t);
 290       dsarand_reseed(&g->d, p, sz);
 291     } break;
 292     case GRAND_SEEDRAND: {
 293       grand *rr = va_arg(ap, grand *);
 294       rr->ops->fill(rr, g->d.p, g->d.sz);
 295     } break;
 296     case DSARAND_PASSES:
 297       g->d.passes = va_arg(ap, unsigned);
 298       break;
 299     default:
 300       GRAND_BADOP;
 301       break;
 302   }
 303
 304   va_end(ap);
 305   return (rc);
 306 }
 307
 308 static void gfill(grand *r, void *p, size_t sz)
 309 {
 310   gctx *g = (gctx *)r;
 311   dsarand_fill(&g->d, p, sz);
 312 }
 313
 314 static const grand_ops gops = {
 315   "dsarand",
 316   0, 0,
 317   gmisc, gdestroy,
 318   grand_word, grand_byte, grand_word, grand_range, gfill
 319 };
 320
 321 /* --- @dsarand_create@ --- *
 322  *
 323  * Arguments:   @const void *p@ = pointer to seed buffer
 324  *              @size_t sz@ = size of seed buffer
 325  *
 326  * Returns:     Pointer to a generic generator.
 327  *
 328  * Use:         Constructs a generic generator interface over a Catacomb
 329  *              entropy pool generator.
 330  */
 331
 332 grand *dsarand_create(const void *p, size_t sz)
 333 {
 334   gctx *g = CREATE(gctx);
 335   g->r.ops = &gops;
 336   dsarand_init(&g->d, p, sz);
 337   return (&g->r);
 338 }
 339
 340 /*----- That's all, folks -------------------------------------------------*/