code: function ARC4init(key) {
    var i, j, t;
    for(i = 0; i < 256; ++i)
      this.S[i] = i;
    j = 0;
    for(i = 0; i < 256; ++i) {
      j = (j + this.S[i] + key[i % key.length]) & 255;
      t = this.S[i];
      this.S[i] = this.S[j];
      this.S[j] = t;
    }
    this.i = 0;
    this.j = 0;
  }
docs: Initialize arcfour context from key, an array of ints, each from [0..255]