code: public static StreamCipher createRC4DropCipher(byte[] key, int drop) {
          checkArgument(key.length >= 5 && key.length <= 256);
          checkArgument(drop > 0);
          RC4Engine rc4Engine = new RC4Engine();
          rc4Engine.init(true, new KeyParameter(key));
          byte[] dropBytes = new byte[drop];
          Arrays.fill(dropBytes, (byte) 0);
          rc4Engine.processBytes(dropBytes, 0, dropBytes.length, dropBytes, 0);
          return rc4Engine;
      }
docs: Creates an RC4-drop cipher
  
  @param key  rc4 key (40..2048 bits)
  @param drop number of bytes to drop
  @return decrypted input stream