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

   1 /* -*-c-*-
   2  *
   3  * $Id: dsarand.c,v 1.4 2004/04/08 01:36:15 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 /*----- Header files ------------------------------------------------------*/
  31
  32 #include <stdarg.h>
  33 #include <string.h>
  34
  35 #include <mLib/alloc.h>
  36 #include <mLib/bits.h>
  37 #include <mLib/sub.h>
  38
  39 #include "dsarand.h"
  40 #include "grand.h"
  41 #include "sha.h"
  42
  43 /*----- Main code ---------------------------------------------------------*/
  44
  45 /* --- @STEP@ --- *
  46  *
  47  * Arguments:   @dsarand *d@ = pointer to context
  48  *
  49  * Use:         Increments the buffer by one, interpreting it as a big-endian
  50  *              integer.  Carries outside the integer are discarded.
  51  */
  52
  53 #define STEP(d) do {                                                    \
  54   dsarand *_d = (d);                                                    \
  55   octet *_p = _d->p;                                                    \
  56   octet *_q = _p + _d->sz;                                              \
  57   unsigned _c = 1;                                                      \
  58   while (_c && _q > _p) {                                               \
  59     _c += *--_q;                                                        \
  60     *_q = U8(_c);                                                       \
  61     _c >>= 8;                                                           \
  62   }                                                                     \
  63 } while (0)
  64
  65 /* --- @dsarand_init@ --- *
  66  *
  67  * Arguments:   @dsarand *d@ = pointer to context
  68  *              @const void *p@ = pointer to seed buffer
  69  *              @size_t sz@ = size of the buffer
  70  *
  71  * Returns:     ---
  72  *
  73  * Use:         Initializes a DSA random number generator.
  74  */
  75
  76 void dsarand_init(dsarand *d, const void *p, size_t sz)
  77 {
  78   d->p = xmalloc(sz);
  79   d->sz = sz;
  80   d->passes = 1;
  81   if (p)
  82     memcpy(d->p, p, sz);
  83 }
  84
  85 /* --- @dsarand_reseed@ --- *
  86  *
  87  * Arguments:   @dsarand *d@ = pointer to context
  88  *              @const void *p@ = pointer to seed buffer
  89  *              @size_t sz@ = size of the buffer
  90  *
  91  * Returns:     ---
  92  *
  93  * Use:         Initializes a DSA random number generator.
  94  */
  95
  96 void dsarand_reseed(dsarand *d, const void *p, size_t sz)
  97 {
  98   xfree(d->p);
  99   d->p = xmalloc(sz);
 100   d->sz = sz;
 101   d->passes = 1;
 102   if (p)
 103     memcpy(d->p, p, sz);
 104 }
 105
 106 /* --- @dsarand_destroy@ --- *
 107  *
 108  * Arguments:   @dsarand *d@ = pointer to context
 109  *
 110  * Returns:     ---
 111  *
 112  * Use:         Disposes of a DSA random number generation context.
 113  */
 114
 115 void dsarand_destroy(dsarand *d)
 116 {
 117   xfree(d->p);
 118 }
 119
 120 /* --- @dsarand_fill@ --- *
 121  *
 122  * Arguments:   @dsarand *d@ = pointer to context
 123  *              @void *p@ = pointer to output buffer
 124  *              @size_t sz@ = size of output buffer
 125  *
 126  * Returns:     ---
 127  *
 128  * Use:         Fills an output buffer with pseudorandom data.
 129  *
 130  *              Let %$p$% be the numerical value of the input buffer, and let
 131  *              %$b$% be the number of bytes required.  Let
 132  *              %$z = \lceil b / 20 \rceil$% be the number of SHA outputs
 133  *              required.  Then the output of pass %$n$% is
 134  *
 135  *                %$P_n = \sum_{0 \le i < z} 2^{160i} SHA(p + nz + i)$%
 136  *                                                      %${} \bmod 2^{8b}$%
 137  *
 138  *              and the actual result in the output buffer is the XOR of all
 139  *              of the output passes.
 140  *
 141  *              The DSA procedure for choosing @q@ involves two passes with
 142  *              %$z = 1$%; the procedure for choosing @p@ involves one pass
 143  *              with larger %$z$%.  This generalization of the DSA generation
 144  *              procedure is my own invention but it seems relatively sound.
 145  */
 146
 147 void dsarand_fill(dsarand *d, void *p, size_t sz)
 148 {
 149   octet *q = p;
 150   unsigned n = d->passes;
 151
 152   /* --- Write out the first pass --- *
 153    *
 154    * This can write directly to the output buffer, so it's done differently
 155    * from the latter passes.
 156    */
 157
 158   {
 159     size_t o = sz;
 160
 161     while (o) {
 162       sha_ctx h;
 163
 164       /* --- Hash the input buffer --- */
 165
 166       sha_init(&h);
 167       sha_hash(&h, d->p, d->sz);
 168
 169       /* --- If enough space, extract the hash output directly --- */
 170
 171       if (o >= SHA_HASHSZ) {
 172         o -= SHA_HASHSZ;
 173         sha_done(&h, q + o);
 174       }
 175
 176       /* --- Otherwise take the hash result out of line and copy it --- */
 177
 178       else {
 179         octet hash[SHA_HASHSZ];
 180         sha_done(&h, hash);
 181         memcpy(q, hash + (SHA_HASHSZ - o), o);
 182         o = 0;
 183       }
 184
 185       /* --- Step the input buffer --- */
 186
 187       STEP(d);
 188     }
 189
 190     /* --- Another pass has been done --- */
 191
 192     n--;
 193   }
 194
 195   /* --- Write out subsequent passes --- *
 196    *
 197    * The hash output has to be done offline, so this is slightly easier.
 198    */
 199
 200   while (n) {
 201     size_t o = sz;
 202
 203     while (o) {
 204       sha_ctx h;
 205       octet hash[SHA_HASHSZ];
 206       size_t n;
 207       octet *pp, *qq;
 208
 209       /* --- Hash the input buffer --- */
 210
 211       sha_init(&h);
 212       sha_hash(&h, d->p, d->sz);
 213       sha_done(&h, hash);
 214
 215       /* --- Work out how much output is wanted --- */
 216
 217       n = SHA_HASHSZ;
 218       if (n > o)
 219         n = o;
 220       o -= n;
 221
 222       /* --- XOR the data out --- */
 223
 224       for (pp = hash + (SHA_HASHSZ - n), qq = q + o;
 225            pp < hash + SHA_HASHSZ; pp++, qq++)
 226         *qq ^= *pp;
 227
 228       /* --- Step the input buffer --- */
 229
 230       STEP(d);
 231     }
 232
 233     /* --- Another pass is done --- */
 234
 235     n--;
 236   }
 237 }
 238
 239 /*----- Generic pseudorandom-number generator interface -------------------*/
 240
 241 static const grand_ops gops;
 242
 243 typedef struct gctx {
 244   grand r;
 245   dsarand d;
 246 } gctx;
 247
 248 static void gdestroy(grand *r)
 249 {
 250   gctx *g = (gctx *)r;
 251   dsarand_destroy(&g->d);
 252   DESTROY(g);
 253 }
 254
 255 static int gmisc(grand *r, unsigned op, ...)
 256 {
 257   gctx *g = (gctx *)r;
 258   va_list ap;
 259   int rc = 0;
 260   va_start(ap, op);
 261
 262   switch (op) {
 263     case GRAND_CHECK:
 264       switch (va_arg(ap, unsigned)) {
 265         case GRAND_CHECK:
 266         case GRAND_SEEDBLOCK:
 267         case GRAND_SEEDRAND:
 268         case DSARAND_PASSES:
 269         case DSARAND_SEEDSZ:
 270         case DSARAND_GETSEED:
 271           rc = 1;
 272           break;
 273         default:
 274           rc = 0;
 275           break;
 276       }
 277       break;
 278     case GRAND_SEEDBLOCK: {
 279       const void *p = va_arg(ap, const void *);
 280       size_t sz = va_arg(ap, size_t);
 281       dsarand_reseed(&g->d, p, sz);
 282     } break;
 283     case GRAND_SEEDRAND: {
 284       grand *rr = va_arg(ap, grand *);
 285       rr->ops->fill(rr, g->d.p, g->d.sz);
 286     } break;
 287     case DSARAND_PASSES:
 288       g->d.passes = va_arg(ap, unsigned);
 289       break;
 290     case DSARAND_SEEDSZ:
 291       rc = g->d.sz;
 292       break;
 293     case DSARAND_GETSEED:
 294       memcpy(va_arg(ap, void *), g->d.p, g->d.sz);
 295       break;
 296     default:
 297       GRAND_BADOP;
 298       break;
 299   }
 300
 301   va_end(ap);
 302   return (rc);
 303 }
 304
 305 static void gfill(grand *r, void *p, size_t sz)
 306 {
 307   gctx *g = (gctx *)r;
 308   dsarand_fill(&g->d, p, sz);
 309 }
 310
 311 static const grand_ops gops = {
 312   "dsarand",
 313   0, 0,
 314   gmisc, gdestroy,
 315   grand_word, grand_byte, grand_word, grand_range, gfill
 316 };
 317
 318 /* --- @dsarand_create@ --- *
 319  *
 320  * Arguments:   @const void *p@ = pointer to seed buffer
 321  *              @size_t sz@ = size of seed buffer
 322  *
 323  * Returns:     Pointer to a generic generator.
 324  *
 325  * Use:         Constructs a generic generator interface over a Catacomb
 326  *              entropy pool generator.
 327  */
 328
 329 grand *dsarand_create(const void *p, size_t sz)
 330 {
 331   gctx *g = CREATE(gctx);
 332   g->r.ops = &gops;
 333   dsarand_init(&g->d, p, sz);
 334   return (&g->r);
 335 }
 336
 337 /*----- That's all, folks -------------------------------------------------*/