用ASP.NET加密Cookie数据(1) 一、.NET的密码系统概要 简单地说，加密就是将原始字符（字节）串转变为完全不同的字符串的处理过程，达到原始字符无法破译的目的。这个处理过程是用另一个字符串（称为“密钥”），采取复杂的、混合的算法，“捣进”原始字符串。有时还使用一个称为“初始向量”的字符串，在密钥捣进之前先打乱目标字符串，预防目标字符串中较明显的内容被识破。加密的功效取决于所用密钥的大小，密钥越长，保密性越强。典型的密钥长度有64位、128位、192位、256位和512位。攻击者唯一的方法是创建一个程序尝试每一个可能的密钥组合，但64位密钥也有72,057,594,037,927,936种组合。 目前有两种加密方法：对称加密（或称私有密钥）和非对称加密（或称公共密钥）。对称加密技术的数据交换两边（即加密方和解密方）必须使用一个保密的私有密钥。非对称加密技术中，解密方向加密方要求一个公共密钥，加密方在建立一个公共密钥给解密方后，用公共密钥创建唯一的私有密钥。加密方用私有密钥加密送出的信息，对方用公共密钥解密。保护HTTP传输安全的SSL就是使用非对称技术。 我们对Cookie数据的加密采取对称加密法。.NET构架从基本的SymmetricAlgorithm类扩展出来四种算法： ·System.Security.Cryptography.DES ·System.Security.Cryptography.TripleDES ·System.Security.Cryptography.RC2 ·System.Security.Cryptography.Rijndael 下面将示范DES和TripleDES算法。DES的密钥大小限制在64位，但用于Cookie的加密是有效的。TripleDES完成了三次加密，并有一个较大的密钥位数，所以它更安全。使用那一种算法不仅要考虑加密强度，还要考虑Cookie的大小。因为加密后的Cookie数据将变大，并且，密钥越大，加密后的数据就越大，然而Cookie数据的大小限制在4KB，这是一个必须考虑的问题。再者，加密的数据越多或算法越复杂，就会占有更多的服务器资源，进而减慢整个站点的访问速度。 二、创建一个简单的加密应用类 .NET的所有加密和解密通过CryptoStream类别来处理，它衍生自System.IO.Stream，将字符串作为以资料流为基础的模型，供加密转换之用。下面是一个简单的加密应用类的代码： Imports System.Diagnostics Imports System.Security.Cryptography Imports System.Text ? Imports System.IO ? Public Class CryptoUtil '随机选8个字节既为密钥也为初始向量 Private Shared KEY_6?) As Byte = {42, 16, 93, 156, 78, 4, 218, 32} Private Shared IV_64() As Byte = {55, 103, 246, 79, 36, 99, 16? 3} '对TripleDES，采取24字节或192位的密钥和初始向量 Private Shared KeY_192() As Byte = {42, 16, 93, 156, 78, 4, 218, 32, _ 15, 167, 44, 80, 26, 250, 155, 112, _ 2, 94, 11, 204, 119, 35, 184, 197} Private Shared IV_192() As Byte = {55, 103, 246, 79, 36, 99, 167, 3, _ 42, 5, 62, 83, 184, 7, 209, 13, _ 145, 23, 200, 58, 173, 10, 121, 222} '标准的DES加密 Public Shared Function Encrypt(ByVal value As String) 羢 String If value <> "" Uhen Dim cryptoProvid錼 羢 DESCryptoServiceProvider = _ - New DESCryptoServiceProvider() Dim ms As MemoryStream = New MemoryStream() Dim cs As CryptoStream = _ New CryptoStream(ms, cryptoProvider.CreateEncryptor(KEY_64, IV_64), _ CryptoStreamMode.Write) Dim sw As StreamWriter = New StreamWriter(cs) sw.Write(value) sw.Flush() cs.FlushFinalBlock() ms.Flush() '再转换为一个字符串 Return Convert.ToBase64String(ms.GetBuffer(), 0, ms.Length) End If End Function
Public Shared Function Decrypt(ByVal value As String) As String If value <> "" Then Dim cryptoProvider As DESCryptoServiceProvider = _ New DESCryptoServiceProvider() '从字符串转换为字节组 Dim buffer As Byte() = Convert.FromBase64String(value) Dim ms As MemoryStream = New MemoryStream(buffer) Dim cs As CryptoStream = _ New CryptoStream(ms, cryptoProvider.CreateDecryptor(KEY_64, IV_64), _ CryptoStreamMode.Read) Dim sr As StreamReader = New StreamReader(cs) Return sr.ReadToEnd() End If End Function 'TRIPLE DES加密 Public Shared Function EncryptTripleDES(ByVal value As String) As String If value <> "" Then Dim cryptoProvider As TripleDESCryptoServiceProvider = _ New TripleDESCryptoServiceProvider() Dim ms As MemoryStream = New MemoryStream() Dim cs As CryptoStream = _ New CryptoStream(ms, cryptoProvider.CreateEncryptor(KEY_192, IV_192), _ CryptoStreamMode.Write) Dim sw As StreamWriter = New StreamWriter(cs) sw.Write(value) sw.Flush() cs.FlushFinalBlock() ms.Flush() '再转换为一个字符串 Return Convert.ToBase64String(ms.GetBuffer(), 0, ms.Length) End If End Function 'TRIPLE DES解密 Public Shared Function DecryptTripleDES(ByVal value As String) As String If value <> "" Then Dim cryptoProvider As TripleDESCryptoServiceProvider = _ New TripleDESCryptoServiceProvider() '从字符串转换为字节组 Dim buffer As Byte() = Convert.FromBase64String(value) Dim ms As MemoryStream = New MemoryStream(buffer) Dim cs As CryptoStream = _ New CryptoStream(ms, cryptoProvider.CreateDecryptor(KEY_192, IV_192), _ CryptoStreamMode.Read) Dim sr As StreamReader = New StreamReader(cs) Return sr.ReadToEnd() End If End Function End Class 上面我们将一组字节初始化为密钥，并且使用的是数字常量，如果你在实际应用中也这样做，这些字节一定要在0和255之间，这是一个字节允许的范围值。 三、创建一个Cookie的应用类 下面我们就创建一个简单的类，来设置和获取Cookies。 Public Class CookieUtil '设置COOKIE ***************************************************** 'SetTripleDESEncryptedCookie （只针对密钥和Cookie数据） Public Shared Sub SetTripleDESEncryptedCookie(ByVal key As String, _ ByVal value As String) key = CryptoUtil.EncryptTripleDES(key) value = CryptoUtil.EncryptTripleDES(value) SetCookie(key, value) End Sub 'SetTripleDESEncryptedCookie （增加了Cookie数据的有效期参数） Public Shared Sub SetTripleDESEncryptedCookie(ByVal key As String, _ ByVal value As String, ByVal expires As Date) key = CryptoUtil.EncryptTripleDES(key) value = CryptoUtil.EncryptTripleDES(value) SetCookie(key, value, expires) End Sub 'SetEncryptedCookie（只针对密钥和Cookie数据） Public Shared Sub SetEncryptedCookie(ByVal key As String, _ ByVal value As String) key = CryptoUtil.Encrypt(key) value = CryptoUtil.Encrypt(value) SetCookie(key, value) End Sub 'SetEncryptedCookie （增加了Cookie数据的有效期参数） Public Shared Sub SetEncryptedCookie(ByVal key As String, _ ByVal value As String, ByVal expires As Date) key = CryptoUtil.Encrypt(key) value = CryptoUtil.Encrypt(value) SetCookie(key, value, expires) End Sub 'SetCookie （只针对密钥和Cookie数据） Public Shared Sub SetCookie(ByVal key As String, ByVal value As String) '编码部分 key = HttpContext.Current.Server.UrlEncode(key) value = HttpContext.Current.Server.UrlEncode(value) Dim cookie As HttpCookie cookie = New HttpCookie(key, value) SetCookie(cookie) End Sub 'SetCookie（增加了Cookie数据的有效期参数） Public Shared Sub SetCookie(ByVal key As String, _ ByVal value As String, ByVal expires As Date) '编码部分 key = HttpContext.Current.Server.UrlEncode(key) value = HttpContext.Current.Server.UrlEncode(value) Dim cookie As HttpCookie cookie = New HttpCookie(key, value) cookie.Expires = expires SetCookie(cookie) End Sub 'SetCookie （只针对HttpCookie） Public Shared Sub SetCookie(ByVal cookie As HttpCookie) HttpContext.Current.Response.Cookies.Set(cookie) End Sub '获取COOKIE ***************************************************** Public Shared Function GetTripleDESEncryptedCookieValue(ByVal key As String) _ As String '只对密钥加密 key = CryptoUtil.EncryptTripleDES(key) '获取Cookie值 Dim value As String value = GetCookieValue(key) '解密Cookie值 value = CryptoUtil.DecryptTripleDES(value) Return value End Function Public Shared Function GetEncryptedCookieValue(ByVal key As String) As String '只对密钥加密 key = CryptoUtil.Encrypt(key) '获取Cookie值 Dim value As String value = GetCookieValue(key) '解密Cookie值 value = CryptoUtil.Decrypt(value) Return value End Function Public Shared Function GetCookie(ByVal key As String) As HttpCookie '编码密钥 key = HttpContext.Current.Server.UrlEncode(key) Return HttpContext.Current.Request.Cookies.Get(key) End Function Public Shared Function GetCookieValue(ByVal key As String) As String Try '编码在GetCookie里完成 '获取Cookie值 Dim value As String value = GetCookie(key).Value '解码所存储的值 value = HttpContext.Current.Server.UrlDecode(value) Return value Catch End Try End Function End Class 上面的设置功能中，有些功能附加提供了Cookie有效期这个参数。不设置该参数，Cookie将只为浏览器会话才保存在内存中。为了设置永久的Cookie，就需要设置有效期参数。 上面我们对密钥和Cookies值进行了编码与解码，其原因是Cookies与URLs有同样的限制，字符“=”和“；”是保留的，不能使用。这在保存加密后的数据时尤其重要，因为加密算法将添加“=”，按所分配块的大小来填满该数据块。 好了，你会保护Cookies数据了吧？
