git.distorted.org.uk Git - u/mdw/catacomb/blob - rand/dsarand.c

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