/// <summary>
 /// 解密
 /// </summary>
 /// <param name="ciphertext ">密文</param>
 /// <returns>解密后的字符串</returns>
 public string Decrypt(string ciphertext) => DESUtil.Decrypt(ciphertext, key, iv);
 /// <summary>
 /// 加密
 /// </summary>
 /// <param name="plaintext">明文</param>
 /// <returns>加密后的字符串</returns>
 public string Encrypt(string plaintext) => DESUtil.Encrypt(plaintext, key, iv);