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

   1 /* -*-c-*-
   2  *
   3  * Key size management
   4  *
   5  * (c) 2007 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 #ifndef CATACOMB_KEYSZ_H
  29 #define CATACOMB_KEYSZ_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #include <stddef.h>
  38
  39 #include <mLib/bits.h>
  40
  41 /*----- Data structures ---------------------------------------------------*/
  42
  43 /* --- Key size type constants --- *
  44  *
  45  * A key size limitation is an array of bytes.  The first byte describes the
  46  * kind of limitation on the key size %$k$%; the rest are argument bytes
  47  * %$a_i$%, for %$i \ge 0$%.  In all cases, %$a_0$% is the `recommended' key
  48  * size.
  49  *
  50  *   * @KSZ_ANY@ means there is no restriction.
  51  *
  52  *   * @KSZ_RANGE@ requires that %$k \ge a_1$%, %$k \equiv 0 \pmod{a_3}$%,
  53  *     and, if %$a_2 \ne 0$%, %$k \le a_2$%.
  54  *
  55  *   * @KSZ_SET@ requires that %$k \in {\,a_i\,}$%.
  56  */
  57
  58 enum {
  59   KSZ_ANY,                              /* Allows any key at all */
  60   KSZ_RANGE,                            /* Allows keys within a range */
  61   KSZ_SET                               /* Allows specific sizes of keys */
  62 };
  63
  64 /*----- Key sizes for symmetric algorithms --------------------------------*/
  65
  66 /* --- @keysz@ --- *
  67  *
  68  * Arguments:   @size_t sz@ = a proposed key size, or zero
  69  *              @const octet *ksz@ = pointer to key size table
  70  *
  71  * Returns:     See below.
  72  *
  73  * Use:         Returns a sensible key size.  If @sz@ is nonzero, it is
  74  *              interpreted as an amount (in bytes) of key material which the
  75  *              caller has available, and the return value is either the
  76  *              largest allowable key size less than or equal to the caller's
  77  *              size, or zero if there is no valid key length small enough.
  78  *              If @sz@ is zero, the function returns a `recommended' key
  79  *              size.
  80  */
  81
  82 extern size_t keysz(size_t /*sz*/, const octet */*ksz*/);
  83
  84 #define KSZ_CHECK(pre, sz) (keysz((sz), pre##_keysz) == (sz))
  85 #define KSZ_ASSERT(pre, sz)                                             \
  86   assert(((void)"Bad key size for " #pre, KSZ_CHECK(pre, sz)))
  87
  88 /*----- That's all, folks -------------------------------------------------*/
  89
  90 #ifdef __cplusplus
  91   }
  92 #endif
  93
  94 #endif