// http://en.wikipedia.org/wiki/RC4_(cipher)
typedef unsigned char ch;
typedef struct {ch s[256]; ch i; ch j;} state;
void mv(ch * out, state * s, int n){
  ch i = s->i, j = s->j; int z;
  for(z = 0; z<n; ++z)
    {ch si = s->s[++i]; j += si; ch sj = s->s[j];
    s->s[i]=sj; s->s[j]=si;
    out[z] = s->s[255&(sj + si)];}
  s->i = i; s->j = j;}

#include <string.h>
void initst(state * st, ch * key)
{{int j=256; while(j--) st->s[j] = j;}
 {int i, j=0, len = strlen((char*)key);
    for(i=0; i<256; ++i) 
     {j = (j + st->s[i] + key[i%len])&255;
     {ch t=st->s[i]; st->s[i]=st->s[j]; st->s[j]=t;}}
    st->i = st->j = 0;}}