git.distorted.org.uk Git - u/mdw/catacomb/blob - symm/rc4.h

   1 /* -*-c-*-
   2  *
   3  * The alleged RC4 stream cipher
   4  *
   5  * (c) 1999 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 /*----- Notes on RC4 ------------------------------------------------------*
  29  *
  30  * RC4 is a stream cipher desgigned by Ron Rivest.  For a while RC4 was a
  31  * trade secret of RSA Data Security, Inc., but somehow source code for a
  32  * cipher which interworks with RC4 was posted to the Cypherpunks mailing
  33  * list.
  34  */
  35
  36 #ifndef CATACOMB_RC4_H
  37 #define CATACOMB_RC4_H
  38
  39 #ifdef __cplusplus
  40   extern "C" {
  41 #endif
  42
  43 /*----- Header files ------------------------------------------------------*/
  44
  45 #include <assert.h>
  46
  47 #include <mLib/bits.h>
  48
  49 #ifndef CATACOMB_GCIPHER_H
  50 #  include "gcipher.h"
  51 #endif
  52
  53 #ifndef CATACOMB_GRAND_H
  54 #  include "grand.h"
  55 #endif
  56
  57 /*----- Data structures ---------------------------------------------------*/
  58
  59 typedef struct rc4_ctx {
  60   unsigned i, j;                        /* Indices into the @S@ table */
  61   unsigned f;                           /* Flags word */
  62   octet s[256];                         /* The ever-changing @S@ table */
  63 } rc4_ctx;
  64
  65 #define RC4F_OPEN 1u
  66
  67 /*----- Macros ------------------------------------------------------------*/
  68
  69 /* --- @RC4_OPEN@ --- *
  70  *
  71  * Arguments:   @ctx@ = pointer to an RC4 context
  72  *              @guts@ = code to perform within the RC4 context
  73  *
  74  * Use:         Performs some code within an RC4 context.  Some of the
  75  *              parameters are extracted from the context and held in local
  76  *              variables for speed.  Multiple calls to @RC4_BYTE@ may be
  77  *              made within the open context.  A context must only be
  78  *              opened once at a time.
  79  */
  80
  81 #define RC4_OPEN(ctx, guts) do {                                        \
  82   unsigned _rc4_i = (ctx)->i;                                           \
  83   unsigned _rc4_j = (ctx)->j;                                           \
  84   octet *_rc4_s = (ctx)->s;                                             \
  85                                                                         \
  86   assert(((void)"RC4 context may only be opened once at a time",        \
  87           ((ctx)->f & RC4F_OPEN) == 0));                                \
  88   (ctx)->f |= RC4F_OPEN;                                                \
  89                                                                         \
  90   guts                                                                  \
  91                                                                         \
  92   (ctx)->f &= ~RC4F_OPEN;                                               \
  93   (ctx)->i = _rc4_i;                                                    \
  94   (ctx)->j = _rc4_j;                                                    \
  95 } while (0)
  96
  97 /* --- @RC4_BYTE@ --- *
  98  *
  99  * Arguments:   @x@ = output variable to set
 100  *
 101  * Use:         Extracts an octet from the lexically innermost open RC4
 102  *              context and places it in the variable @x@.
 103  */
 104
 105 #define RC4_BYTE(x) do {                                                \
 106   unsigned _si, _sj;                                                    \
 107   _rc4_i = (_rc4_i + 1) & 0xff;                                         \
 108   _si = _rc4_s[_rc4_i];                                                 \
 109   _rc4_j = (_rc4_j + _si) & 0xff;                                       \
 110   _sj = _rc4_s[_rc4_j];                                                 \
 111   _rc4_s[_rc4_i] = _sj;                                                 \
 112   _rc4_s[_rc4_j] = _si;                                                 \
 113   (x) = _rc4_s[(_si + _sj) & 0xff];                                     \
 114 } while (0)
 115
 116 /*----- Functions provided ------------------------------------------------*/
 117
 118 /* --- @rc4_addkey@ --- *
 119  *
 120  * Arguments:   @rc4_ctx *ctx@ = pointer to context to key
 121  *              @const void *k@ = pointer to key data to use
 122  *              @size_t sz@ = size of the key data
 123  *
 124  * Returns:     ---
 125  *
 126  * Use:         Mixes key data with an RC4 context.  The RC4 context is not
 127  *              reset before mixing.  This may be used to mix new key
 128  *              material with an existing RC4 context.
 129  */
 130
 131 extern void rc4_addkey(rc4_ctx */*ctx*/, const void */*k*/, size_t /*sz*/);
 132
 133 /* --- @rc4_init@ --- *
 134  *
 135  * Arguments:   @rc4_ctx *ctx@ = pointer to context to initialize
 136  *              @const void *k@ = pointer to key data to use
 137  *              @size_t sz@ = size of the key data
 138  *
 139  * Returns:     ---
 140  *
 141  * Use:         Initializes an RC4 context ready for use.
 142  */
 143
 144 extern void rc4_init(rc4_ctx */*ctx*/, const void */*k*/, size_t /*sz*/);
 145
 146 /* --- @rc4_encrypt@ --- *
 147  *
 148  * Arguments:   @rc4_ctx *ctx@ = pointer to context to use
 149  *              @const void *src@ = pointer to the source block
 150  *              @void *dest@ = pointer to the destination block
 151  *              @size_t sz@ = size of the block
 152  *
 153  * Returns:     ---
 154  *
 155  * Use:         Encrypts or decrypts a block of data.  The destination may
 156  *              be null to just grind the generator around for a while.  It's
 157  *              recommended that you say `@rc4_encrypt(&ctx, 0, 0, 1024)@'
 158  *              after initializing a new context, to prevent keystream
 159  *              guessing attacks.  The source may be null to just extract a
 160  *              big lump of data from the generator.
 161  */
 162
 163 extern void rc4_encrypt(rc4_ctx */*ctx*/,
 164                         const void */*src*/, void */*dest*/,
 165                         size_t /*sz*/);
 166
 167 /*----- Generic cipher interface ------------------------------------------*/
 168
 169 #define RC4_KEYSZ 16
 170 extern const octet rc4_keysz[];
 171
 172 extern const gccipher rc4;
 173
 174 /*----- Generic random number generator interface -------------------------*/
 175
 176 /* --- @rc4_rand@ --- *
 177  *
 178  * Arguments:   @const void *k@ = pointer to key material
 179  *              @size_t sz@ = size of key material
 180  *
 181  * Returns:     Pointer to generic random number generator interface.
 182  *
 183  * Use:         Creates a random number interface wrapper around an
 184  *              OFB-mode block cipher.
 185  */
 186
 187 extern grand *rc4_rand(const void */*k*/, size_t /*sz*/);
 188
 189 /*----- That's all, folks -------------------------------------------------*/
 190
 191 #ifdef __cplusplus
 192   }
 193 #endif
 194
 195 #endif