C#:实现DES加密算法
/// <summary>
/// DES加密字符串
/// </summary>
/// <param name="encryptString">待加密的字符串</param>
/// <param name="encryptKey">加密密钥,要求为8位</param>
/// <returns>加密成功返回加密后的字符串,失败返回源串</returns>
public string EncryptDES(