方法一：
    //须添加对System.Web的引用
    using System.Web.Security;
     
    …
     
    ///

    /// SHA1加密字符串     ///

    /// 源字符串
    /// 加密后的字符串
    public string SHA1(string source)
    {
        return FormsAuthentication.HashPasswordForStoringInConfigFile(source, "SHA1");
    }
 
 
    ///

    /// MD5加密字符串     ///

    /// 源字符串
    /// 加密后的字符串
    public string MD5(string source)
    {
        return FormsAuthentication.HashPasswordForStoringInConfigFile(source, "MD5");;
    }

方法五：
    using System.IO;
    using System.Security.Cryptography;
    using System.Text;
     
    …
     
    //默认密钥向量
    private static byte[] Keys = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
    ///

    /// DES加密字符串     ///

    /// 待加密的字符串
    /// 加密密钥,要求为8位
    /// 加密成功返回加密后的字符串，失败返回源串
    public static string EncryptDES(string encryptString, string encryptKey)
    {
        try
        {
            byte[] rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));
            byte[] rgbIV = Keys;
            byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptString);
            DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider();
            MemoryStream mStream = new MemoryStream();
            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;
        }
    }
     
    ///

    /// DES解密字符串     ///

    /// 待解密的字符串
    /// 解密密钥,要求为8位,和加密密钥相同
    /// 解密成功返回解密后的字符串，失败返源串
    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;
        }
    }

方法六(文件加密)：
    using System.IO;
    using System.Security.Cryptography;
    using System.Text;
     
    …
     
    //加密文件
    private static void EncryptData(String inName, String outName, byte[] desKey, byte[] desIV)
    {
        //Create the file streams to handle the input and output files.
        FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
        FileStream fout = new FileStream(outName, FileMode.OpenOrCreate, FileAccess.Write);
        fout.SetLength(0);
     
        //Create variables to help with read and write.
        byte[] bin = new byte[100]; //This is intermediate storage for the encryption.
        long rdlen = 0;              //This is the total number of bytes written.
        long totlen = fin.Length;    //This is the total length of the input file.
        int len;                     //This is the number of bytes to be written at a time.
     
        DES des = new DESCryptoServiceProvider();
        CryptoStream encStream = new CryptoStream(fout, des.CreateEncryptor(desKey, desIV), CryptoStreamMode.Write);
     
        //Read from the input file, then encrypt and write to the output file.
        while (rdlen < totlen)
        {
            len = fin.Read(bin, 0, 100);
            encStream.Write(bin, 0, len);
            rdlen = rdlen + len;
        }
     
        encStream.Close();
        fout.Close();
        fin.Close();
    }
     
    //解密文件
    private static void DecryptData(String inName, String outName, byte[] desKey, byte[] desIV)
    {
        //Create the file streams to handle the input and output files.
        FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
        FileStream fout = new FileStream(outName, FileMode.OpenOrCreate, FileAccess.Write);
        fout.SetLength(0);
     
        //Create variables to help with read and write.
        byte[] bin = new byte[100]; //This is intermediate storage for the encryption.
        long rdlen = 0;              //This is the total number of bytes written.
        long totlen = fin.Length;    //This is the total length of the input file.
        int len;                     //This is the number of bytes to be written at a time.
     
        DES des = new DESCryptoServiceProvider();
        CryptoStream encStream = new CryptoStream(fout, des.CreateDecryptor(desKey, desIV), CryptoStreamMode.Write);
     
        //Read from the input file, then encrypt and write to the output file.
        while (rdlen < totlen)
        {
            len = fin.Read(bin, 0, 100);
            encStream.Write(bin, 0, len);
            rdlen = rdlen + len;
        }
     
        encStream.Close();
        fout.Close();
        fin.Close();
 
}

原文地址：http://www.cnblogs.com/zengxiangzhan/archive/2010/01/30/1659687.html