code: func NewCast5BlockCrypt(key []byte) (BlockCrypt, error) {
  	c := new(cast5BlockCrypt)
  	block, err := cast5.NewCipher(key)
  	if err != nil {
  		return nil, err
  	}
  	c.block = block
  	return c, nil
  }
docs: // NewCast5BlockCrypt https://en.wikipedia.org/wiki/CAST-128