// Solitaire Cipher algorithm: Bruce Schneier -> http://schneier.com/solitaire.html //
// Implementation by: B-Con (Brad Conte)                                            //
//////////////////////////////////////////////////////////////////////////////////////

#include <stdio.h>
#include <string.h>
#define CARDS 54
#define JOKER_A 53
#define JOKER_B 54

char find_move_joker(char deck[], char joker) {
   char idx=0,temp,joker_index,new_index;
   while (deck[idx] != joker)
      joker_index = ++idx;
   temp = deck[joker_index];
   new_index = (joker_index + 1) % CARDS;
   if (!new_index)
      new_index++;
   deck[joker_index] = deck[new_index];
   deck[new_index] = temp;
   return(new_index);
}   

void three_way_split(char deck[], char hi, char low) {
   char temp[CARDS];
   memcpy(temp,&deck[low+1],CARDS-1-low);
   memcpy(&temp[CARDS-1-low],&deck[hi],low-hi+1);
   memcpy(&temp[CARDS-1-hi+1],deck,hi);
   memcpy(deck,temp,CARDS);
}

void count_cut(char deck[], char count) {
   char temp[CARDS];
   deck[count] == JOKER_B ? (count = JOKER_A) : (count = deck[CARDS-1]);
   memcpy(temp,&deck[count],CARDS-1-count);
   memcpy(&temp[CARDS-1-count],deck,count);

   memcpy(deck,temp,CARDS-1);
}

void init_deck(char deck[], char key[]) {
   unsigned char idx,joker_a,joker_b,len=strlen(key);
   for (idx=0; idx < len; idx++)
      key[idx] >= 'a' && key[idx] <= 'z' ? (key[idx] -= 'a' - 26 - 1) : (key[idx] -= 'A' - 1);
   for (idx=0; idx < CARDS; idx++)
      deck[idx] = idx + 1;
   for (idx=0; idx < len; idx++) {
      joker_a = find_move_joker(deck,JOKER_A);
      joker_b = find_move_joker(deck,JOKER_B);
      joker_b = find_move_joker(deck,JOKER_B);
      joker_a < joker_b ? three_way_split(deck,joker_a,joker_b) : three_way_split(deck,joker_b,joker_a);
      count_cut(deck,deck[CARDS-1]);
      count_cut(deck,key[idx]);
   }   
}

void gen_keystream(char deck[], char keystream[], int len) {
   char temp[CARDS],joker_a,joker_b,new_key;
   int idx;
   for (idx=0; idx < len; idx++) {
      joker_a = find_move_joker(deck,JOKER_A);
      joker_b = find_move_joker(deck,JOKER_B);
      joker_b = find_move_joker(deck,JOKER_B);
      joker_a < joker_b ? three_way_split(deck,joker_a,joker_b) : three_way_split(deck,joker_b,joker_a);
      count_cut(deck,deck[CARDS-1]);
      new_key = deck[deck[0]];
      if (new_key == JOKER_A || new_key == JOKER_B)
         idx--;
      else
         (new_key > 26) ? (keystream[idx] = new_key + ('a' - 26 - 1)) : (keystream[idx] = new_key + ('A' - 1));
   }   
} 

int main() {
   char deck[CARDS],deck_init_key[256],key_len[8],keystream[2048]={0};
   printf("Key: ");
   gets(deck_init_key);
   init_deck(deck,deck_init_key);
   printf("Length of keystream: ");
   gets(key_len);
   gen_keystream(deck,keystream,atoi(key_len));
   printf("Keystream: ");
   puts(keystream);
   getchar();
   return 0;
}