Pollard's rho algorithm for computing discrete logs.

[u/mdw/catacomb] / oaep.c

/* -*-c-*-
 *
 * $Id: oaep.c,v 1.1 2000/07/01 11:18:30 mdw Exp $
 *
 * Optimal asymmetric encryption packing
 *
 * (c) 2000 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * 
 * Catacomb is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: oaep.c,v $
 * Revision 1.1  2000/07/01 11:18:30  mdw
 * Support for Optimal Asymmetric Encryption Padding.
 *
 */

/*----- Header files ------------------------------------------------------*/

#include <string.h>

#include <mLib/alloc.h>
#include <mLib/bits.h>
#include <mLib/dstr.h>

#include "gcipher.h"
#include "ghash.h"
#include "grand.h"
#include "oaep.h"

/*----- Main code ---------------------------------------------------------*/

/* --- @oaep_encode@ --- *
 *
 * Arguments:	@const void *msg@ = pointer to message data
 *		@size_t msz@ = size of message data
 *		@void *buf@ = pointer to output buffer
 *		@size_t sz@ = size of the output buffer
 *		@void *p@ = pointer to OAEP parameter block
 *
 * Returns:	Zero if all went well, negative on failure.
 *
 * Use:		Implements the operation @EME-OAEP-ENCODE@, as defined in
 *		PKCS#1 v. 2.0 (RFC2437).
 */

int oaep_encode(const void *msg, size_t msz, void *buf, size_t sz, void *p)
{
  oaep *o = p;
  size_t hsz = o->ch->hashsz;
  ghash *h = o->ch->init();
  octet *q, *mq, *qq;
  octet *pp;
  gcipher *c;
  size_t n;

  /* --- Ensure that everything is sensibly sized --- */

  if (2 * hsz + 2 + msz > sz)
    return (-1);

  /* --- Make the `seed' value --- */

  q = buf;
  *q++ = 0; sz--;
  mq = q + hsz;
  qq = q + sz;
  o->r->ops->fill(o->r, q, hsz);

  /* --- Fill in the rest of the buffer --- */

  h->ops->hash(h, o->ep, o->epsz);
  h->ops->done(h, mq);
  h->ops->destroy(h);
  pp = mq + hsz;
  n = sz - 2 * hsz - msz - 1;
  memset(pp, 0, n);
  pp += n;
  *pp++ = 1;
  memcpy(pp, msg, msz);

  /* --- Do the packing --- */

  n = sz - hsz;
  c = o->cc->init(q, hsz);
  c->ops->encrypt(c, mq, mq, n);
  c->ops->destroy(c);

  c = o->cc->init(mq, n);
  c->ops->encrypt(c, q, q, hsz);
  c->ops->destroy(c);

  /* --- Done --- */

  return (0);
}

/* --- @oaep_decode@ --- *
 *
 * Arguments:	@const void *buf@ = pointer to encoded buffer
 *		@size_t sz@ = size of the encoded buffer
 *		@dstr *d@ = pointer to destination string
 *		@void *p@ = pointer to OAEP parameter block
 *
 * Returns:	The length of the output string if successful, negative on
 *		failure.
 *
 * Use:		Implements the operation @EME-OAEP-DECODE@, as defined in
 *		PKCS#1 v. 2.0 (RFC2437).
 */

int oaep_decode(const void *buf, size_t sz, dstr *d, void *p)
{
  oaep *o = p;
  gcipher *c;
  ghash *h;
  octet *q, *mq, *qq;
  octet *pp;
  size_t n;
  size_t hsz = o->ch->hashsz;
  int rc = -1;

  /* --- Ensure that the block is large enough --- */

  if (sz < 2 * hsz)
    return (-1);

  q = x_alloc(d->a, sz);
  memcpy(q, buf, sz);

  /* --- Decrypt the message --- */

  if (*q != 0)
    goto fail;
  q++; sz--;
  mq = q + hsz;
  qq = q + sz;
  n = sz - hsz;
  c = o->cc->init(mq, n);
  c->ops->decrypt(c, q, q, hsz);
  c->ops->destroy(c);

  c = o->cc->init(q, hsz);
  c->ops->decrypt(c, mq, mq, n);
  c->ops->destroy(c);
  q--;

  /* --- Check the hash on the encoding parameters --- */

  h = o->ch->init();
  h->ops->hash(h, o->ep, o->epsz);
  h->ops->done(h, q);
  if (memcmp(q, mq, hsz) != 0)
    goto fail;

  /* --- Now find the start of the actual message --- */

  pp = mq + hsz;
  while (*pp == 0 && pp < qq)
    pp++;
  if (pp >= qq || *pp++ != 1)
    return (-1);
  n = qq - pp;
  dstr_putm(d, pp, n);
  rc = n;

fail:
  x_free(d->a, q);
  return (rc);
}

/*----- That's all, folks -------------------------------------------------*/