[u/mdw/catacomb] / keysz.c

/* -*-c-*-
 *
 * $Id: keysz.c,v 1.2 2004/04/08 01:36:15 mdw Exp $
 *
 * General block cipher utilities
 *
 * (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.
 */

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

#include <assert.h>

#include "gcipher.h"

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

/* --- @keysz@ --- *
 *
 * Arguments:	@size_t sz@ = a proposed key size, or zero
 *		@const octet *ksz@ = pointer to key size table
 *
 * Returns:	See below.
 *
 * Use:		Returns a sensible key size.  If @sz@ is nonzero, it is
 *		interpreted as an amount (in bytes) of key material which the
 *		caller has available, and the return value is either the
 *		largest allowable key size less than or equal to the caller's
 *		size, or zero if there is no valid key length small enough.
 *		If @sz@ is zero, the function returns a `recommended' key
 *		size.
 */

size_t keysz(size_t sz, const octet *ksz)
{
  if (sz == 0)
    return (ksz[1]);
  else switch (ksz[0]) {
    case KSZ_ANY:
      return (sz);
    case KSZ_RANGE:
      if (ksz[4])
	sz -= sz % ksz[4];
      if (sz < ksz[2])
	return (0);
      if (ksz[3] && sz > ksz[3])
	return (ksz[3]);
      return (sz);
    case KSZ_SET: {
      unsigned q = 0;
      for (ksz++; *ksz; ksz++) {
	if (sz >= *ksz && q < *ksz)
	  q = *ksz;
      }
      return (q);
    }
  }

  assert(((void)"bad key size table", 0));
  return (0);
}

/*----- That's all, folks -------------------------------------------------*/
Commit	Line	Data
7809fc3d	1	/* --c--
7809fc3d	2	*
b817bfc6	3	* $Id: keysz.c,v 1.2 2004/04/08 01:36:15 mdw Exp $
7809fc3d	4	*
	5	* General block cipher utilities
	6	*
	7	* (c) 2000 Straylight/Edgeware
	8	*/
	9
45c0fd36	10	/----- Licensing notice --------------------------------------------------
7809fc3d	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.
45c0fd36	18	*
7809fc3d	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.
45c0fd36	23	*
7809fc3d	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
7809fc3d	30	/----- Header files ------------------------------------------------------/
	31
	32	#include <assert.h>
	33
	34	#include "gcipher.h"
	35
	36	/----- Main code ---------------------------------------------------------/
	37
	38	/* --- @keysz@ --- *
	39	*
	40	* Arguments: @size_t sz@ = a proposed key size, or zero
	41	* @const octet *ksz@ = pointer to key size table
	42	*
	43	* Returns: See below.
	44	*
	45	* Use: Returns a sensible key size. If @sz@ is nonzero, it is
	46	* interpreted as an amount (in bytes) of key material which the
	47	* caller has available, and the return value is either the
	48	* largest allowable key size less than or equal to the caller's
	49	* size, or zero if there is no valid key length small enough.
	50	* If @sz@ is zero, the function returns a `recommended' key
	51	* size.
	52	*/
	53
	54	size_t keysz(size_t sz, const octet *ksz)
	55	{
	56	if (sz == 0)
	57	return (ksz[1]);
	58	else switch (ksz[0]) {
	59	case KSZ_ANY:
	60	return (sz);
	61	case KSZ_RANGE:
	62	if (ksz[4])
	63	sz -= sz % ksz[4];
	64	if (sz < ksz[2])
	65	return (0);
	66	if (ksz[3] && sz > ksz[3])
	67	return (ksz[3]);
	68	return (sz);
	69	case KSZ_SET: {
	70	unsigned q = 0;
	71	for (ksz++; *ksz; ksz++) {
	72	if (sz >= ksz && q < ksz)
	73	q = *ksz;
	74	}
	75	return (q);
	76	}
	77	}
	78
	79	assert(((void)"bad key size table", 0));
	80	return (0);
	81	}
	82
	83	/----- That's all, folks -------------------------------------------------/