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

   1 /* -*-c-*-
   2  *
   3  * $Id: pss.c,v 1.2 2004/04/08 01:36:15 mdw Exp $
   4  *
   5  * Probabistic signature scheme
   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 <string.h>
  33
  34 #include <mLib/alloc.h>
  35 #include <mLib/bits.h>
  36 #include <mLib/dstr.h>
  37
  38 #include "gcipher.h"
  39 #include "ghash.h"
  40 #include "grand.h"
  41 #include "rsa.h"
  42
  43 /*----- Magic statics -----------------------------------------------------*/
  44
  45 static const octet z8[8] = { 0 };
  46
  47 /*----- Main code ---------------------------------------------------------*/
  48
  49 /* --- @pss_encode@ --- *
  50  *
  51  * Arguments:   @mp *d@ = where to put the answer
  52  *              @const void *m@ = pointer to the message hash
  53  *              @size_t msz@ = the size of the message hash
  54  *              @octet *b@ = scratch buffer
  55  *              @size_t sz@ = sizeo of the buffer (large enough)
  56  *              @unsigned long nbits@ = size in bits of @n@
  57  *              @void *p@ = pointer to the PSS parameters
  58  *
  59  * Returns:     Encoded message representative, or null on error.
  60  *
  61  * Use:         Implements the operation @EMSA-PSS-ENCODE@, as defined in
  62  *              PKCS#1 v. 2.1 (RFC3447).
  63  */
  64
  65 mp *pss_encode(mp *d, const void *m, size_t msz, octet *b, size_t sz,
  66                unsigned long nbits, void *p)
  67 {
  68   pss *pp = p;
  69   octet *s, *r;
  70   ghash *h;
  71   gcipher *c;
  72   unsigned mask;
  73   size_t pssz, hsz = pp->ch->hashsz;
  74
  75   /* --- Check the message length --- */
  76
  77   nbits--;
  78   sz = (nbits + 7)/8;
  79   mask = (1 << nbits%8) - 1;
  80   if (!mask) mask = 0xff;
  81   if (hsz + pp->ssz + 2 > sz)
  82     return (0);
  83
  84   /* --- Generate a random salt --- */
  85
  86   pssz = sz - pp->ssz - hsz - 2;
  87   memset(b, 0, pssz);
  88   b[pssz] = 0x01;
  89   s = b + pssz + 1;
  90   r = s + pp->ssz;
  91   GR_FILL(pp->r, s, pp->ssz);
  92
  93   /* --- Compute the salted hash --- */
  94
  95   h = GH_INIT(pp->ch);
  96   GH_HASH(h, z8, 8);
  97   GH_HASH(h, m, msz);
  98   GH_HASH(h, s, pp->ssz);
  99   GH_DONE(h, r);
 100   r[hsz] = 0xbc;
 101
 102   /* --- Do the masking --- */
 103
 104   c = GC_INIT(pp->cc, r, hsz);
 105   GC_ENCRYPT(c, b, b, pssz + pp->ssz + 1);
 106   GC_DESTROY(c);
 107   b[0] &= mask;
 108   return (mp_loadb(d, b, sz));
 109 }
 110
 111 /* --- @pss_decode@ --- *
 112  *
 113  * Arguments:   @mp *s@ = the message representative
 114  *              @const void *m@ = the original message
 115  *              @size_t msz@ = the message size
 116  *              @octet *b@ = a scratch buffer
 117  *              @size_t sz@ = size of the buffer (large enough)
 118  *              @unsigned long nbits@ = number of bits in @n@
 119  *              @void *p@ = pointer to PKCS1 parameters
 120  *
 121  * Returns:     The length of the output string if successful, negative on
 122  *              failure.
 123  *
 124  * Use:         Implements the operation @EMSA_PSS_VERIFY@, as defined in
 125  *              PCSK#1 v. 2.1 (RFC3447).
 126  */
 127
 128 int pss_decode(mp *mi, const void *m, size_t msz, octet *b, size_t sz,
 129                unsigned long nbits, void *p)
 130 {
 131   pss *pp = p;
 132   octet *s, *r;
 133   ghash *h;
 134   gcipher *c;
 135   unsigned mask;
 136   size_t pssz, hsz = pp->ch->hashsz, i;
 137   int rc;
 138
 139   /* --- Check the message length --- */
 140
 141   nbits--;
 142   sz = (nbits + 7)/8;
 143   if (mp_octets(mi) > sz)
 144     return (-1);
 145   mask = (1 << nbits%8) - 1;
 146   if (!mask) mask = 0xff;
 147   if (hsz + pp->ssz + 2 > sz)
 148     return (-1);
 149   mp_storeb(mi, b, sz);
 150
 151   /* --- Split up the buffer --- */
 152
 153   pssz = sz - hsz - pp->ssz - 2;
 154   s = b + pssz + 1;
 155   r = s + pp->ssz;
 156   if (r[hsz] != 0xbc)
 157     return (-1);
 158
 159   /* --- Decode the seed --- */
 160
 161   if (b[0] & ~mask)
 162     return (-1);
 163   c = GC_INIT(pp->cc, r, hsz);
 164   GC_DECRYPT(c, b, b, pssz + pp->ssz + 1);
 165   GC_DESTROY(c);
 166   b[0] &= mask;
 167   for (i = 0; i < pssz; i++)
 168     if (b[i]) return (-1);
 169   if (b[pssz] != 0x01)
 170     return (-1);
 171
 172   /* --- Hash the message --- */
 173
 174   h = GH_INIT(pp->ch);
 175   GH_HASH(h, z8, 8);
 176   GH_HASH(h, m, msz);
 177   GH_HASH(h, s, pp->ssz);
 178   s = GH_DONE(h, 0);
 179   rc = !memcmp(s, r, hsz);
 180   GH_DESTROY(h);
 181   if (!rc) return (-1);
 182
 183   /* --- Done --- */
 184
 185   return (0);
 186 }
 187
 188 /*----- That's all, folks -------------------------------------------------*/