arcfour.c

   1 /*
   2  * File:                arcfour.c
   3  * Author:      Daniel Otte
   4  * Date:        07.06.2006
   5  * License: GPL
   6  * Description: Implementation of the ARCFOUR (RC4 compatible) stream cipher algorithm.
   7  *
   8  */
   9
  10 #include <stdint.h>
  11 #include "arcfour.h"
  12
  13 /*
  14  * length is length of key in bytes!
  15  */
  16
  17 void arcfour_init(arcfour_ctx_t *c, uint8_t *key, uint8_t length){
  18         uint8_t t;
  19         unsigned x,y=0;
  20         for(x=0; x<= 255; ++x)
  21                 c->s[x]=x;
  22
  23         for(x=0; x<= 255; ++x){
  24                 y += c->s[x] + key[x % length];
  25                 y &= 0xff;
  26                 t = c->s[y];
  27                 c->s[y] = c->s[x];
  28                 c->s[x] = t;
  29         };
  30
  31         c->i = c->j = 0;
  32 }
  33
  34 uint8_t arcfour_gen(arcfour_ctx_t *c){
  35         uint8_t t;
  36         c->i++;
  37         c->j += c->s[c->i];
  38         t = c->s[c->j];
  39         c->s[c->j] = c->s[c->i];
  40         c->s[c->i] = t;
  41         return c->s[(c->s[c->j] + c->s[c->i]) & 0xff];
  42 }
  43