1.添加引用

using System.Security.Cryptography;
using System.IO;

2.添加默认密匙向量

//默认密钥向量
private static byte[] Keys = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

3.添加加密解密类

/// <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 static string EncryptDES(string encryptString, string encryptKey)
{
    try
    {
    byte[] rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));//转换为字节
    byte[] rgbIV = Keys;
    byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptString);
    DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider();//实例化数据加密标准
    MemoryStream mStream = new MemoryStream();//实例化内存流
    //将数据流链接到加密转换的流
    CryptoStream cStream = new CryptoStream(mStream, dCSP.CreateEncryptor(rgbKey, rgbIV),CryptoStreamMode.Write);
    cStream.Write(inputByteArray, 0, inputByteArray.Length);
    cStream.FlushFinalBlock();
    return Convert.ToBase64String(mStream.ToArray());
    }
    catch
    {
        return encryptString;
    }
}

/// <summary>
/// DES解密字符串
/// </summary>
/// <param name="decryptString">待解密的字符串</param>
/// <param name="decryptKey">解密密钥,要求为8位,和加密密钥相同</param>
/// <returns>解密成功返回解密后的字符串，失败返源串</returns>
public static string DecryptDES(string decryptString, string decryptKey)
{
    try
    {
    byte[] rgbKey = Encoding.UTF8.GetBytes(decryptKey);
    byte[] rgbIV = Keys;
    byte[] inputByteArray = Convert.FromBase64String(decryptString);
    DESCryptoServiceProvider DCSP = new DESCryptoServiceProvider();
    MemoryStream mStream = new MemoryStream();
    CryptoStream cStream = new CryptoStream(mStream, DCSP.CreateDecryptor(rgbKey, rgbIV),CryptoStreamMode.Write);
    cStream.Write(inputByteArray, 0, inputByteArray.Length);
    cStream.FlushFinalBlock();
    return Encoding.UTF8.GetString(mStream.ToArray());
    }
    catch
    {
        return decryptString;
    }
}

4.调用方法（在文章结尾，有相关类，编译后直接调用即可）

//返回加密后的字符串EncryptStr
string EncryptStr = EncryptDESString.EncryptDES("This is a Test", "password");  
MessageBox.Show(EncryptStr);
//解密字符串EncryptStr
string DecryptStr = EncryptDESString.DecryptDES(EncryptStr, "password");
MessageBox.Show(EncryptStr);

加密后：

解密后：

本文出自 “世界都一样” 博客，请务必保留此出处http://970076933.blog.51cto.com/9767314/1885616

C#DES加密解密字符串