Cookie確實(shí)在WEB應(yīng)用方面為訪問(wèn)者和編程者都提供了方便，然而從安全方面考慮是有問(wèn)題的，首先，Cookie數(shù)據(jù)包含在HTTP請(qǐng)求和響應(yīng)的包頭里透明地傳遞，也就是說(shuō)聰明的人是能清清楚楚看到這些數(shù)據(jù)的。其次，Cookie數(shù)據(jù)以Cookie文件格式存儲(chǔ)在瀏覽者計(jì)算機(jī)的cache目錄里，其中就包含有關(guān)網(wǎng)頁(yè)、密碼和其他用戶行為的信息，那么只要進(jìn)入硬盤就能打開(kāi)Cookie文件。圖1是一個(gè)Cookie文件的內(nèi)容：

如果你未曾留意你的機(jī)器里有Cookie文件，可以按下列方法查看：打開(kāi)IE，選擇“工具”菜單里的“Internet選項(xiàng)”，然后在彈出的對(duì)話框里點(diǎn)擊“設(shè)置”按鈕，在設(shè)置對(duì)話框里點(diǎn)擊“查看”鈕，就會(huì)打開(kāi)一個(gè)窗口顯示瀏覽器放在硬盤里的所有緩存數(shù)據(jù)，其中就有大量的Cookie文件。
所以奉勸大家不要將敏感的用戶數(shù)據(jù)存放在Cookie中，要么就通過(guò)加密將這些數(shù)據(jù)保護(hù)起來(lái)。
在以前的ASP版本中沒(méi)有加密的功能，現(xiàn)在.NET構(gòu)架在System.Security.Cryptography命名空間里提供了許多加密類可以利用。
一、.NET的密碼系統(tǒng)概要
簡(jiǎn)單地說(shuō)，加密就是將原始字符（字節(jié)）串轉(zhuǎn)變?yōu)橥耆煌淖址奶幚磉^(guò)程，達(dá)到原始字符無(wú)法破譯的目的。這個(gè)處理過(guò)程是用另一個(gè)字符串（稱為“密鑰”），采取復(fù)雜的、混合的算法，“搗進(jìn)”原始字符串。有時(shí)還使用一個(gè)稱為“初始向量”的字符串，在密鑰搗進(jìn)之前先打亂目標(biāo)字符串，預(yù)防目標(biāo)字符串中較明顯的內(nèi)容被識(shí)破。加密的功效取決于所用密鑰的大小，密鑰越長(zhǎng)，保密性越強(qiáng)。典型的密鑰長(zhǎng)度有64位、128位、192位、256位和512位。攻擊者唯一的方法是創(chuàng)建一個(gè)程序嘗試每一個(gè)可能的密鑰組合，但64位密鑰也有72,057,594,037,927,936種組合。
目前有兩種加密方法：對(duì)稱加密（或稱私有密鑰）和非對(duì)稱加密（或稱公共密鑰）。對(duì)稱加密技術(shù)的數(shù)據(jù)交換兩邊（即加密方和解密方）必須使用一個(gè)保密的私有密鑰。非對(duì)稱加密技術(shù)中，解密方向加密方要求一個(gè)公共密鑰，加密方在建立一個(gè)公共密鑰給解密方后，用公共密鑰創(chuàng)建唯一的私有密鑰。加密方用私有密鑰加密送出的信息，對(duì)方用公共密鑰解密。保護(hù)HTTP傳輸安全的SSL就是使用非對(duì)稱技術(shù)。
我們對(duì)Cookie數(shù)據(jù)的加密采取對(duì)稱加密法。.NET構(gòu)架從基本的SymmetricAlgorithm類擴(kuò)展出來(lái)四種算法：
·System.Security.Cryptography.DES
·System.Security.Cryptography.TripleDES
·System.Security.Cryptography.RC2
·System.Security.Cryptography.Rijndael
下面將示范DES和TripleDES算法。DES的密鑰大小限制在64位，但用于Cookie的加密是有效的。TripleDES完成了三次加密，并有一個(gè)較大的密鑰位數(shù)，所以它更安全。使用那一種算法不僅要考慮加密強(qiáng)度，還要考慮Cookie的大小。因?yàn)榧用芎蟮腃ookie數(shù)據(jù)將變大，并且，密鑰越大，加密后的數(shù)據(jù)就越大，然而Cookie數(shù)據(jù)的大小限制在4KB，這是一個(gè)必須考慮的問(wèn)題。再者，加密的數(shù)據(jù)越多或算法越復(fù)雜，就會(huì)占有更多的服務(wù)器資源，進(jìn)而減慢整個(gè)站點(diǎn)的訪問(wèn)速度。
二、創(chuàng)建一個(gè)簡(jiǎn)單的加密應(yīng)用類
.NET的所有加密和解密通過(guò)CryptoStream類別來(lái)處理，它衍生自System.IO.Stream，將字符串作為以資料流為基礎(chǔ)的模型，供加密轉(zhuǎn)換之用。下面是一個(gè)簡(jiǎn)單的加密應(yīng)用類的代碼：
Imports System.Diagnostics
Imports System.Security.Cryptography
Imports System.Text
Imports System.IO
Public Class CryptoUtil
'隨機(jī)選8個(gè)字節(jié)既為密鑰也為初始向量
Private Shared KEY_64() As Byte = {42, 16, 93, 156, 78, 4, 218, 32}
Private Shared IV_64() As Byte = {55, 103, 246, 79, 36, 99, 167, 3}
'對(duì)TripleDES，采取24字節(jié)或192位的密鑰和初始向量
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}
'標(biāo)準(zhǔn)的DES加密
Public Shared Function Encrypt(ByVal value As String) As String
If value "" Then
Dim cryptoProvider As 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()
'再轉(zhuǎn)換為一個(gè)字符串
Return Convert.ToBase64String(ms.GetBuffer(), 0, ms.Length)
End If
End Function
'標(biāo)準(zhǔn)的DES解密
Public Shared Function Decrypt(ByVal value As String) As String
If value "" Then
Dim cryptoProvider As DESCryptoServiceProvider = _
New DESCryptoServiceProvider()
'從字符串轉(zhuǎn)換為字節(jié)組
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
'標(biāo)準(zhǔn)的DES解密
Public Shared Function Decrypt(ByVal value As String) As String
If value <> "" Then
Dim cryptoProvider As DESCryptoServiceProvider = _
New DESCryptoServiceProvider()
'從字符串轉(zhuǎn)換為字節(jié)組
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()
'再轉(zhuǎn)換為一個(gè)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()
'從字符串轉(zhuǎn)換為字節(jié)組
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
上面我們將一組字節(jié)初始化為密鑰，并且使用的是數(shù)字常量，如果你在實(shí)際應(yīng)用中也這樣做，這些字節(jié)一定要在0和255之間，這是一個(gè)字節(jié)允許的范圍值。
三、創(chuàng)建一個(gè)Cookie的應(yīng)用類
下面我們就創(chuàng)建一個(gè)簡(jiǎn)單的類，來(lái)設(shè)置和獲取Cookies。
Public Class CookieUtil
'設(shè)置COOKIE *****************************************************
'SetTripleDESEncryptedCookie （只針對(duì)密鑰和Cookie數(shù)據(jù)）
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數(shù)據(jù)的有效期參數(shù)）
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（只針對(duì)密鑰和Cookie數(shù)據(jù)）
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數(shù)據(jù)的有效期參數(shù)）
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 （只針對(duì)密鑰和Cookie數(shù)據(jù)）
Public Shared Sub SetCookie(ByVal key As String, ByVal value As String)
'編碼部分
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數(shù)據(jù)的有效期參數(shù)）
Public Shared Sub SetCookie(ByVal key As String, _
ByVal value As String, ByVal expires As Date)
'編碼部分
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 （只針對(duì)HttpCookie）
Public Shared Sub SetCookie(ByVal cookie As HttpCookie)
HttpContext.Current.Response.Cookies.Set(cookie)
End Sub
'獲取COOKIE *****************************************************
Public Shared Function GetTripleDESEncryptedCookieValue(ByVal key As String) _
As String
'只對(duì)密鑰加密
key = CryptoUtil.EncryptTripleDES(key)
'獲取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
'只對(duì)密鑰加密
key = CryptoUtil.Encrypt(key)
'獲取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
'編碼密鑰
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
'編碼在GetCookie里完成
'獲取Cookie值
Dim value As String
value = GetCookie(key).Value
'解碼所存儲(chǔ)的值
value = HttpContext.Current.Server.UrlDecode(value)
Return value
Catch
End Try
End Function
End Class
上面的設(shè)置功能中，有些功能附加提供了Cookie有效期這個(gè)參數(shù)。不設(shè)置該參數(shù)，Cookie將只為瀏覽器會(huì)話才保存在內(nèi)存中。為了設(shè)置永久的Cookie，就需要設(shè)置有效期參數(shù)。
上面我們對(duì)密鑰和Cookies值進(jìn)行了編碼與解碼，其原因是Cookies與URLs有同樣的限制，字符“=”和“；”是保留的，不能使用。這在保存加密后的數(shù)據(jù)時(shí)尤其重要，因?yàn)榧用芩惴▽⑻砑印?”，按所分配塊的大小來(lái)填滿該數(shù)據(jù)塊。
好了，你會(huì)保護(hù)Cookies數(shù)據(jù)了吧？