C#来一段DES加解密代码

在C#中，你可以使用System.Security.Cryptography命名空间下的`DESCryptoServiceProvider`类来进行DES（Data Encryption Standard）加密和解密操作。这里是一个简单的示例：

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

// 加密函数
public static string DES_encrypt(string plainText, string key)
{
    DESCryptoServiceProvider des = new DESCryptoServiceProvider();
    byte[] salt = des.GenerateSalt(8); // DES盐值长度通常为8字节

    using (MemoryStream ms = new MemoryStream())
    {
        using (RijndaelManaged aes = new RijndaelManaged())
        {
            aes.Key = Encoding.ASCII.GetBytes(key);
            aes.IV = salt;
            aes.Mode = CipherMode.CBC; // 使用CBC模式
            ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

            ms.Write(salt, 0, salt.Length);
            using (CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
            {
                using (StreamWriter sw = new StreamWriter(cs))
                {
                    sw.Write(plainText);
                }
            }

            return Convert.ToBase64String(ms.ToArray());
        }
    }
}

// 解密函数
public static string DES_decrypt(string encryptedText, string key)
{
    DESCryptoServiceProvider des = new DESCryptoServiceProvider();
    byte[] encryptedBytes = Convert.FromBase64String(encryptedText);
    byte[] salt = new byte[8];
    Array.Copy(encryptedBytes, salt, 8); // 提取盐值

    using (MemoryStream ms = new MemoryStream())
    {
        ms.Write(salt, 0, salt.Length);
        ms.Write(encryptedBytes, 8, encryptedBytes.Length - 8);

        using (RijndaelManaged aes = new RijndaelManaged())
        {
            aes.Key = Encoding.ASCII.GetBytes(key);
            aes.IV = salt;
            aes.Mode = CipherMode.CBC;

            ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
            using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))
            {
                using (StreamReader sr = new StreamReader(cs))
                {
                    return sr.ReadToEnd();
                }
            }
        }
    }
}

请注意，这个例子中使用的是Rijndael而不是DES，因为DES的安全强度已经不足以满足现代需求。上述代码假设输入的key是ASCII编码的字符串。