mdw@git.distorted.org.uk Git - 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  * RC4 has some quite bad biases, and its use for cryptographic purposes is
  36  * no longer recommended.
  37  */
  38
  39 #ifndef CATACOMB_RC4_H
  40 #define CATACOMB_RC4_H
  41
  42 #ifdef __cplusplus
  43   extern "C" {
  44 #endif
  45
  46 /*----- Header files ------------------------------------------------------*/
  47
  48 #include <assert.h>
  49
  50 #include <mLib/bits.h>
  51
  52 #ifndef CATACOMB_GCIPHER_H
  53 #  include "gcipher.h"
  54 #endif
  55
  56 #ifndef CATACOMB_GRAND_H
  57 #  include "grand.h"
  58 #endif
  59
  60 /*----- Data structures ---------------------------------------------------*/
  61
  62 typedef struct rc4_ctx {
  63   unsigned i, j;                        /* Indices into the @S@ table */
  64   unsigned f;                           /* Flags word */
  65   octet s[256];                         /* The ever-changing @S@ table */
  66 } rc4_ctx;
  67
  68 #define RC4F_OPEN 1u
  69
  70 /*----- Macros ------------------------------------------------------------*/
  71
  72 /* --- @RC4_OPEN@ --- *
  73  *
  74  * Arguments:   @ctx@ = pointer to an RC4 context
  75  *              @guts@ = code to perform within the RC4 context
  76  *
  77  * Use:         Performs some code within an RC4 context.  Some of the
  78  *              parameters are extracted from the context and held in local
  79  *              variables for speed.  Multiple calls to @RC4_BYTE@ may be
  80  *              made within the open context.  A context must only be
  81  *              opened once at a time.
  82  */
  83
  84 #define RC4_OPEN(ctx, guts) do {                                        \
  85   unsigned _rc4_i = (ctx)->i;                                           \
  86   unsigned _rc4_j = (ctx)->j;                                           \
  87   octet *_rc4_s = (ctx)->s;                                             \
  88                                                                         \
  89   assert(((void)"RC4 context may only be opened once at a time",        \
  90           ((ctx)->f & RC4F_OPEN) == 0));                                \
  91   (ctx)->f |= RC4F_OPEN;                                                \
  92                                                                         \
  93   guts                                                                  \
  94                                                                         \
  95   (ctx)->f &= ~RC4F_OPEN;                                               \
  96   (ctx)->i = _rc4_i;                                                    \
  97   (ctx)->j = _rc4_j;                                                    \
  98 } while (0)
  99
 100 /* --- @RC4_BYTE@ --- *
 101  *
 102  * Arguments:   @x@ = output variable to set
 103  *
 104  * Use:         Extracts an octet from the lexically innermost open RC4
 105  *              context and places it in the variable @x@.
 106  */
 107
 108 #define RC4_BYTE(x) do {                                                \
 109   unsigned _si, _sj;                                                    \
 110   _rc4_i = (_rc4_i + 1) & 0xff;                                         \
 111   _si = _rc4_s[_rc4_i];                                                 \
 112   _rc4_j = (_rc4_j + _si) & 0xff;                                       \
 113   _sj = _rc4_s[_rc4_j];                                                 \
 114   _rc4_s[_rc4_i] = _sj;                                                 \
 115   _rc4_s[_rc4_j] = _si;                                                 \
 116   (x) = _rc4_s[(_si + _sj) & 0xff];                                     \
 117 } while (0)
 118
 119 /*----- Functions provided ------------------------------------------------*/
 120
 121 /* --- @rc4_addkey@ --- *
 122  *
 123  * Arguments:   @rc4_ctx *ctx@ = pointer to context to key
 124  *              @const void *k@ = pointer to key data to use
 125  *              @size_t sz@ = size of the key data
 126  *
 127  * Returns:     ---
 128  *
 129  * Use:         Mixes key data with an RC4 context.  The RC4 context is not
 130  *              reset before mixing.  This may be used to mix new key
 131  *              material with an existing RC4 context.
 132  */
 133
 134 extern void rc4_addkey(rc4_ctx */*ctx*/, const void */*k*/, size_t /*sz*/);
 135
 136 /* --- @rc4_init@ --- *
 137  *
 138  * Arguments:   @rc4_ctx *ctx@ = pointer to context to initialize
 139  *              @const void *k@ = pointer to key data to use
 140  *              @size_t sz@ = size of the key data
 141  *
 142  * Returns:     ---
 143  *
 144  * Use:         Initializes an RC4 context ready for use.
 145  */
 146
 147 extern void rc4_init(rc4_ctx */*ctx*/, const void */*k*/, size_t /*sz*/);
 148
 149 /* --- @rc4_encrypt@ --- *
 150  *
 151  * Arguments:   @rc4_ctx *ctx@ = pointer to context to use
 152  *              @const void *src@ = pointer to the source block
 153  *              @void *dest@ = pointer to the destination block
 154  *              @size_t sz@ = size of the block
 155  *
 156  * Returns:     ---
 157  *
 158  * Use:         Encrypts or decrypts a block of data.  The destination may
 159  *              be null to just grind the generator around for a while.  It's
 160  *              recommended that you say `@rc4_encrypt(&ctx, 0, 0, 1024)@'
 161  *              after initializing a new context, to prevent keystream
 162  *              guessing attacks.  The source may be null to just extract a
 163  *              big lump of data from the generator.
 164  */
 165
 166 extern void rc4_encrypt(rc4_ctx */*ctx*/,
 167                         const void */*src*/, void */*dest*/,
 168                         size_t /*sz*/);
 169
 170 /*----- Generic cipher interface ------------------------------------------*/
 171
 172 #define RC4_KEYSZ 16
 173 extern const octet rc4_keysz[];
 174
 175 extern const gccipher rc4;
 176
 177 /*----- Generic random number generator interface -------------------------*/
 178
 179 /* --- @rc4_rand@ --- *
 180  *
 181  * Arguments:   @const void *k@ = pointer to key material
 182  *              @size_t sz@ = size of key material
 183  *
 184  * Returns:     Pointer to generic random number generator interface.
 185  *
 186  * Use:         Creates a random number interface wrapper around the RC4
 187  *              stream cipher.
 188  */
 189
 190 extern grand *rc4_rand(const void */*k*/, size_t /*sz*/);
 191
 192 /*----- That's all, folks -------------------------------------------------*/
 193
 194 #ifdef __cplusplus
 195   }
 196 #endif
 197
 198 #endif