首先在web.config | app.config 文件下增加如下代码：

<?xml version="1.0"?><configuration><appSettings><add key="IV" value="SuFjcEmp/TE="/><add key="Key" value="KIPSToILGp6fl+3gXJvMsN4IajizYBBT"/></appSettings></configuration>

IV:加密算法的初始向量。

Key：加密算法的密钥。

接着新建类CryptoHelper,作为加密帮助类。

首先要从配置文件中得到IV 和Key。所以基本代码如下：

public class CryptoHelper{//private readonly string IV = "SuFjcEmp/TE=";private readonly string IV = string.Empty;//private readonly string Key = "KIPSToILGp6fl+3gXJvMsN4IajizYBBT";private readonly string Key = string.Empty;/// <summary>///构造函数/// </summary>public CryptoHelper(){IV = ConfigurationManager.AppSettings["IV"];Key = ConfigurationManager.AppSettings["Key"];}}

注意添加System.Configuration.dll程序集引用。

在获得了IV 和Key 之后，需要获取提供加密服务的Service 类。

在这里，使用的是System.Security.Cryptography; 命名空间下的TripleDESCryptoServiceProvider类。

获取TripleDESCryptoServiceProvider 的方法如下：

/// <summary>/// 获取加密服务类/// </summary>/// <returns></returns>private TripleDESCryptoServiceProvider GetCryptoProvider(){TripleDESCryptoServiceProvider provider = new TripleDESCryptoServiceProvider();provider.IV = Convert.FromBase64String(IV);provider.Key = Convert.FromBase64String(Key);return provider;}

TripleDESCryptoServiceProvider 两个有用的方法

CreateEncryptor:创建对称加密器对象ICryptoTransform.

CreateDecryptor:创建对称解密器对象ICryptoTransform

加密器对象和解密器对象可以被CryptoStream对象使用。来对流进行加密和解密。

cryptoStream 的构造函数如下：

public CryptoStream(Stream stream, ICryptoTransform transform, CryptoStreamMode mode);

使用transform 对象对stream 进行转换。

完整的加密字符串代码如下：

/// <summary>/// 获取加密后的字符串/// </summary>/// <param name="inputValue">输入值.</param>/// <returns></returns>public string GetEncryptedValue(string inputValue){TripleDESCryptoServiceProvider provider = this.GetCryptoProvider();// 创建内存流来保存加密后的流MemoryStream mStream = new MemoryStream();// 创建加密转换流CryptoStream cStream = new CryptoStream(mStream,provider.CreateEncryptor(), CryptoStreamMode.Write);// 使用UTF8编码获取输入字符串的字节。byte[] toEncrypt = new UTF8Encoding().GetBytes(inputValue);// 将字节写到转换流里面去。cStream.Write(toEncrypt, 0, toEncrypt.Length);cStream.FlushFinalBlock();// 在调用转换流的FlushFinalBlock方法后，内部就会进行转换了,此时mStream就是加密后的流了。byte[] ret = mStream.ToArray();// Close the streams.cStream.Close();mStream.Close();//将加密后的字节进行64编码。return Convert.ToBase64String(ret);}

解密方法也类似：

/// <summary>/// 获取解密后的值/// </summary>/// <param name="inputValue">经过加密后的字符串.</param>/// <returns></returns>public string GetDecryptedValue(string inputValue){TripleDESCryptoServiceProvider provider = this.GetCryptoProvider();byte[] inputEquivalent = Convert.FromBase64String(inputValue);// 创建内存流保存解密后的数据MemoryStream msDecrypt = new MemoryStream();// 创建转换流。CryptoStream csDecrypt = new CryptoStream(msDecrypt,provider.CreateDecryptor(),CryptoStreamMode.Write);csDecrypt.Write(inputEquivalent, 0, inputEquivalent.Length);csDecrypt.FlushFinalBlock();csDecrypt.Close();//获取字符串。return new UTF8Encoding().GetString(msDecrypt.ToArray());}

完整的CryptoHelper代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;
using System.IO;
using System.Configuration;namespace WindowsFormsApplication1
{public class CryptoHelper{//private readonly string IV = "SuFjcEmp/TE=";private readonly string IV = string.Empty;//private readonly string Key = "KIPSToILGp6fl+3gXJvMsN4IajizYBBT";private readonly string Key = string.Empty;public CryptoHelper(){IV = ConfigurationManager.AppSettings["IV"];Key = ConfigurationManager.AppSettings["Key"];}/// <summary>/// 获取加密后的字符串/// </summary>/// <param name="inputValue">输入值.</param>/// <returns></returns>public string GetEncryptedValue(string inputValue){TripleDESCryptoServiceProvider provider = this.GetCryptoProvider();// 创建内存流来保存加密后的流MemoryStream mStream = new MemoryStream();// 创建加密转换流CryptoStream cStream = new CryptoStream(mStream,provider.CreateEncryptor(), CryptoStreamMode.Write);// 使用UTF8编码获取输入字符串的字节。byte[] toEncrypt = new UTF8Encoding().GetBytes(inputValue);// 将字节写到转换流里面去。cStream.Write(toEncrypt, 0, toEncrypt.Length);cStream.FlushFinalBlock();// 在调用转换流的FlushFinalBlock方法后，内部就会进行转换了,此时mStream就是加密后的流了。byte[] ret = mStream.ToArray();// Close the streams.cStream.Close();mStream.Close();//将加密后的字节进行64编码。return Convert.ToBase64String(ret);}/// <summary>/// 获取加密服务类/// </summary>/// <returns></returns>private TripleDESCryptoServiceProvider GetCryptoProvider(){TripleDESCryptoServiceProvider provider = new TripleDESCryptoServiceProvider();provider.IV = Convert.FromBase64String(IV);provider.Key = Convert.FromBase64String(Key);return provider;}/// <summary>/// 获取解密后的值/// </summary>/// <param name="inputValue">经过加密后的字符串.</param>/// <returns></returns>public string GetDecryptedValue(string inputValue){TripleDESCryptoServiceProvider provider = this.GetCryptoProvider();byte[] inputEquivalent = Convert.FromBase64String(inputValue);// 创建内存流保存解密后的数据MemoryStream msDecrypt = new MemoryStream();// 创建转换流。CryptoStream csDecrypt = new CryptoStream(msDecrypt,provider.CreateDecryptor(),CryptoStreamMode.Write);csDecrypt.Write(inputEquivalent, 0, inputEquivalent.Length);csDecrypt.FlushFinalBlock();csDecrypt.Close();//获取字符串。return new UTF8Encoding().GetString(msDecrypt.ToArray());}}
}

使用例子：

原文地址：http://blogs.msdn.com/b/nikhiln/archive/2008/05/18/net-2-0-symmetric-encryption-code-sample.aspx