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

   1 /* -*-c-*-
   2  *
   3  * Optimal asymmetric encryption packing
   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 "ct.h"
  37 #include "gcipher.h"
  38 #include "ghash.h"
  39 #include "grand.h"
  40 #include "rsa.h"
  41
  42 /*----- Main code ---------------------------------------------------------*/
  43
  44 /* --- @oaep_encode@ --- *
  45  *
  46  * Arguments:   @mp *d@ = where to put the answer
  47  *              @const void *m@ = pointer to message data
  48  *              @size_t msz@ = size of message data
  49  *              @octet *b@ = spare buffer
  50  *              @size_t sz@ = size of the buffer (big enough)
  51  *              @unsigned long nbits@ = length of bits of @n@
  52  *              @void *p@ = pointer to OAEP parameter block
  53  *
  54  * Returns:     The encoded plaintext, or null on failure.
  55  *
  56  * Use:         Implements the operation @EME-OAEP-ENCODE@, as defined in
  57  *              PKCS#1 v. 2.0 (RFC2437).
  58  */
  59
  60 mp *oaep_encode(mp *d, const void *m, size_t msz, octet *b, size_t sz,
  61                 unsigned long nbits, void *p)
  62 {
  63   oaep *o = p;
  64   size_t hsz = o->ch->hashsz;
  65   ghash *h;
  66   octet *q, *mq;
  67   octet *pp;
  68   gcipher *c;
  69   size_t n;
  70
  71   /* --- Ensure that everything is sensibly sized --- */
  72
  73   if (2 * hsz + 2 + msz > sz)
  74     return (0);
  75
  76   /* --- Make the `seed' value --- */
  77
  78   q = b;
  79   *q++ = 0; sz--;
  80   mq = q + hsz;
  81   GR_FILL(o->r, q, hsz);
  82
  83   /* --- Fill in the rest of the buffer --- */
  84
  85   h = GH_INIT(o->ch);
  86   GH_HASH(h, o->ep, o->epsz);
  87   GH_DONE(h, mq);
  88   GH_DESTROY(h);
  89   pp = mq + hsz;
  90   n = sz - 2 * hsz - msz - 1;
  91   memset(pp, 0, n);
  92   pp += n;
  93   *pp++ = 1;
  94   memcpy(pp, m, msz);
  95
  96   /* --- Do the packing --- */
  97
  98   n = sz - hsz;
  99   c = GC_INIT(o->cc, q, hsz);
 100   GC_ENCRYPT(c, mq, mq, n);
 101   GC_DESTROY(c);
 102
 103   c = GC_INIT(o->cc, mq, n);
 104   GC_ENCRYPT(c, q, q, hsz);
 105   GC_DESTROY(c);
 106
 107   /* --- Done --- */
 108
 109   return (mp_loadb(d, b, sz + 1));
 110 }
 111
 112 /* --- @oaep_decode@ --- *
 113  *
 114  * Arguments:   @mp *m@ = the decrypted message
 115  *              @octet *b@ = pointer to a buffer to work in
 116  *              @size_t sz@ = the size of the buffer (big enough)
 117  *              @unsigned long nbits@ = the number of bits in @n@
 118  *              @void *p@ = pointer to OAEP parameter block
 119  *
 120  * Returns:     The length of the output string if successful, negative on
 121  *              failure.
 122  *
 123  * Use:         Implements the operation @EME-OAEP-DECODE@, as defined in
 124  *              PKCS#1 v. 2.0 (RFC2437).
 125  */
 126
 127 int oaep_decode(mp *m, octet *b, size_t sz, unsigned long nbits, void *p)
 128 {
 129   oaep *o = p;
 130   gcipher *c;
 131   ghash *h;
 132   octet *q, *mq, *qq;
 133   octet *pp;
 134   uint32 goodp = 1;
 135   size_t n;
 136   size_t hsz = o->ch->hashsz;
 137
 138   /* --- Ensure that the block is large enough --- */
 139
 140   if (sz < 2 * hsz)                     /* Doesn't depend on ciphertext */
 141     return (-1);
 142
 143   /* --- Decrypt the message --- */
 144
 145   mp_storeb(m, b, sz);
 146   q = b;
 147   goodp &= ct_inteq(*q, 0);
 148   q++; sz--;
 149   mq = q + hsz;
 150   qq = q + sz;
 151   n = sz - hsz;
 152   c = GC_INIT(o->cc, mq, n);
 153   GC_DECRYPT(c, q, q, hsz);
 154   GC_DESTROY(c);
 155
 156   c = GC_INIT(o->cc, q, hsz);
 157   GC_DECRYPT(c, mq, mq, n);
 158   GC_DESTROY(c);
 159   q--;
 160
 161   /* --- Check the hash on the encoding parameters --- */
 162
 163   h = GH_INIT(o->ch);
 164   GH_HASH(h, o->ep, o->epsz);
 165   GH_DONE(h, q);
 166   GH_DESTROY(h);
 167   goodp &= ct_memeq(q, mq, hsz);
 168
 169   /* --- Now find the start of the actual message --- */
 170
 171   pp = mq + hsz;
 172   while (*pp == 0 && pp < qq)
 173     pp++;
 174   goodp &= ~ct_intle(qq - b, pp - b);
 175   goodp &= ct_inteq(*pp, 1);
 176   pp++;
 177   n = qq - pp;
 178   memmove(q, pp, n);
 179   return (goodp ? n : -1);
 180 }
 181
 182 /*----- That's all, folks -------------------------------------------------*/