plugins/excel/rc4.c

   1 #include "rc4.h"
   2
   3 static void
   4 swap_byte (unsigned char *a, unsigned char *b)
   5 {
   6     unsigned char swapByte;
   7
   8     swapByte = *a;
   9     *a = *b;
  10     *b = swapByte;
  11 }
  12
  13 void
  14 prepare_key (unsigned char *key_data_ptr, int key_data_len, RC4_KEY *key)
  15 {
  16     unsigned char index1;
  17     unsigned char index2;
  18     unsigned char *state;
  19     unsigned int counter;
  20
  21     state = &key->state[0];
  22     for (counter = 0; counter < 256; counter++)
  23         state[counter] = counter;
  24     key->x = 0;
  25     key->y = 0;
  26     index1 = 0;
  27     index2 = 0;
  28     for (counter = 0; counter < 256; counter++)
  29       {
  30           index2 = (key_data_ptr[index1] + state[counter] + index2) % 256;
  31           swap_byte (&state[counter], &state[index2]);
  32
  33           index1 = (index1 + 1) % key_data_len;
  34       }
  35 }
  36
  37 void
  38 rc4 (unsigned char *buffer_ptr, unsigned buffer_len, RC4_KEY *key)
  39 {
  40     unsigned char x;
  41     unsigned char y;
  42     unsigned char *state;
  43     unsigned char xorIndex;
  44     unsigned int counter;
  45
  46     x = key->x;
  47     y = key->y;
  48
  49     state = key->state;
  50     for (counter = 0; counter < buffer_len; counter++)
  51       {
  52           x = (x + 1) % 256;
  53           y = (state[x] + y) % 256;
  54           swap_byte (&state[x], &state[y]);
  55
  56           xorIndex = (state[x] + state[y]) % 256;
  57
  58           buffer_ptr[counter] ^= state[xorIndex];
  59       }
  60     key->x = x;
  61     key->y = y;
  62 }
  63