code: func NewSimpleXORBlockCrypt(key []byte) (BlockCrypt, error) {
  	c := new(simpleXORBlockCrypt)
  	c.xortbl = pbkdf2.Key(key, []byte(saltxor), 32, mtuLimit, sha1.New)
  	return c, nil
  }
docs: // NewSimpleXORBlockCrypt simple xor with key expanding