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

   1 /* -*-c-*-
   2  *
   3  * Probabistic signature scheme
   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 <string.h>
  31
  32 #include <mLib/alloc.h>
  33 #include <mLib/bits.h>
  34 #include <mLib/dstr.h>
  35
  36 #include "gcipher.h"
  37 #include "ghash.h"
  38 #include "grand.h"
  39 #include "rsa.h"
  40
  41 /*----- Magic statics -----------------------------------------------------*/
  42
  43 static const octet z8[8] = { 0 };
  44
  45 /*----- Main code ---------------------------------------------------------*/
  46
  47 /* --- @pss_encode@ --- *
  48  *
  49  * Arguments:   @mp *d@ = where to put the answer
  50  *              @const void *m@ = pointer to the message hash
  51  *              @size_t msz@ = the size of the message hash
  52  *              @octet *b@ = scratch buffer
  53  *              @size_t sz@ = sizeo of the buffer (large enough)
  54  *              @unsigned long nbits@ = size in bits of @n@
  55  *              @void *p@ = pointer to the PSS parameters
  56  *
  57  * Returns:     Encoded message representative, or null on error.
  58  *
  59  * Use:         Implements the operation @EMSA-PSS-ENCODE@, as defined in
  60  *              PKCS#1 v. 2.1 (RFC3447).
  61  */
  62
  63 mp *pss_encode(mp *d, const void *m, size_t msz, octet *b, size_t sz,
  64                unsigned long nbits, void *p)
  65 {
  66   pss *pp = p;
  67   octet *s, *r;
  68   ghash *h;
  69   gcipher *c;
  70   unsigned mask;
  71   size_t pssz, hsz = pp->ch->hashsz;
  72
  73   /* --- Check the message length --- */
  74
  75   nbits--;
  76   sz = (nbits + 7)/8;
  77   mask = (1 << nbits%8) - 1;
  78   if (!mask) mask = 0xff;
  79   if (hsz + pp->ssz + 2 > sz)
  80     return (0);
  81
  82   /* --- Generate a random salt --- */
  83
  84   pssz = sz - pp->ssz - hsz - 2;
  85   memset(b, 0, pssz);
  86   b[pssz] = 0x01;
  87   s = b + pssz + 1;
  88   r = s + pp->ssz;
  89   GR_FILL(pp->r, s, pp->ssz);
  90
  91   /* --- Compute the salted hash --- */
  92
  93   h = GH_INIT(pp->ch);
  94   GH_HASH(h, z8, 8);
  95   GH_HASH(h, m, msz);
  96   GH_HASH(h, s, pp->ssz);
  97   GH_DONE(h, r);
  98   r[hsz] = 0xbc;
  99
 100   /* --- Do the masking --- */
 101
 102   c = GC_INIT(pp->cc, r, hsz);
 103   GC_ENCRYPT(c, b, b, pssz + pp->ssz + 1);
 104   GC_DESTROY(c);
 105   b[0] &= mask;
 106   return (mp_loadb(d, b, sz));
 107 }
 108
 109 /* --- @pss_decode@ --- *
 110  *
 111  * Arguments:   @mp *s@ = the message representative
 112  *              @const void *m@ = the original message
 113  *              @size_t msz@ = the message size
 114  *              @octet *b@ = a scratch buffer
 115  *              @size_t sz@ = size of the buffer (large enough)
 116  *              @unsigned long nbits@ = number of bits in @n@
 117  *              @void *p@ = pointer to PKCS1 parameters
 118  *
 119  * Returns:     The length of the output string if successful, negative on
 120  *              failure.
 121  *
 122  * Use:         Implements the operation @EMSA_PSS_VERIFY@, as defined in
 123  *              PCSK#1 v. 2.1 (RFC3447).
 124  */
 125
 126 int pss_decode(mp *mi, const void *m, size_t msz, octet *b, size_t sz,
 127                unsigned long nbits, void *p)
 128 {
 129   pss *pp = p;
 130   octet *s, *r;
 131   ghash *h;
 132   gcipher *c;
 133   unsigned mask;
 134   size_t pssz, hsz = pp->ch->hashsz, i;
 135   int rc;
 136
 137   /* --- Check the message length --- */
 138
 139   nbits--;
 140   sz = (nbits + 7)/8;
 141   if (mp_octets(mi) > sz)
 142     return (-1);
 143   mask = (1 << nbits%8) - 1;
 144   if (!mask) mask = 0xff;
 145   if (hsz + pp->ssz + 2 > sz)
 146     return (-1);
 147   mp_storeb(mi, b, sz);
 148
 149   /* --- Split up the buffer --- */
 150
 151   pssz = sz - hsz - pp->ssz - 2;
 152   s = b + pssz + 1;
 153   r = s + pp->ssz;
 154   if (r[hsz] != 0xbc)
 155     return (-1);
 156
 157   /* --- Decode the seed --- */
 158
 159   if (b[0] & ~mask)
 160     return (-1);
 161   c = GC_INIT(pp->cc, r, hsz);
 162   GC_DECRYPT(c, b, b, pssz + pp->ssz + 1);
 163   GC_DESTROY(c);
 164   b[0] &= mask;
 165   for (i = 0; i < pssz; i++)
 166     if (b[i]) return (-1);
 167   if (b[pssz] != 0x01)
 168     return (-1);
 169
 170   /* --- Hash the message --- */
 171
 172   h = GH_INIT(pp->ch);
 173   GH_HASH(h, z8, 8);
 174   GH_HASH(h, m, msz);
 175   GH_HASH(h, s, pp->ssz);
 176   s = GH_DONE(h, 0);
 177   rc = !memcmp(s, r, hsz);
 178   GH_DESTROY(h);
 179   if (!rc) return (-1);
 180
 181   /* --- Done --- */
 182
 183   return (0);
 184 }
 185
 186 /*----- That's all, folks -------------------------------------------------*/