mdw@git.distorted.org.uk Git - 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   unsigned op = ksz[0]&KSZ_OPMASK;
  55   unsigned wd = (ksz[0]&KSZ_16BIT) ? 2 : 1;
  56   unsigned t, u, v;
  57
  58   ksz++;
  59 #define ARG(i) (wd == 1 ? ksz[i] : LOAD16(ksz + 2*i))
  60   if (sz == 0)
  61     return (ARG(0));
  62   else switch (op) {
  63     case KSZ_ANY: return (sz);
  64     case KSZ_RANGE:
  65       t = ARG(1); u = ARG(2); v = ARG(3);
  66       if (v) sz -= sz%v;
  67       if (sz < t) return (0);
  68       if (u && sz > u) return (u);
  69       return (sz);
  70     case KSZ_SET:
  71       u = 0;
  72       for (;;) {
  73         t = ARG(0); ksz += wd; if (!t) break;
  74         if (sz >= t && u < t) u = t;
  75       }
  76       return (u);
  77   }
  78 #undef ARG
  79
  80   assert(((void)"bad key size table", 0));
  81   return (0);
  82 }
  83
  84 /*----- That's all, folks -------------------------------------------------*/