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

   1 /* -*-c-*-
   2  *
   3  * $Id: keysz.c,v 1.2 2004/04/08 01:36:15 mdw Exp $
   4  *
   5  * General block cipher utilities
   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 <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 -------------------------------------------------*/