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

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