SQL Server 2008中的代碼安全（六）對(duì)稱密鑰加密

更新時(shí)間：2011年06月16日 23:17:23 作者：

證書(shū)和非對(duì)稱密鑰使用數(shù)據(jù)庫(kù)級(jí)的內(nèi)部公鑰加密數(shù)據(jù)，并且使用數(shù)據(jù)庫(kù)級(jí)內(nèi)部私鑰解密數(shù)據(jù)。而對(duì)稱密鑰相對(duì)簡(jiǎn)單，它們包含一個(gè)同時(shí)用來(lái)加密和解密的密鑰。困此，使用對(duì)稱密鑰加密數(shù)據(jù)更快，并且用在大數(shù)據(jù)時(shí)更加合適。盡管復(fù)雜度是考慮使用它的因素，但它仍然是一個(gè)很好的加密數(shù)據(jù)的選擇。

我們看一組例子：

示例一、創(chuàng)建對(duì)稱密鑰

對(duì)稱密鑰的特性是：在數(shù)據(jù)庫(kù)會(huì)話中使用它對(duì)數(shù)據(jù)進(jìn)行加密和解密前必須首先打開(kāi)。

創(chuàng)建對(duì)稱密鑰使用如下命令:CREATE SYMMETRIC KEY 創(chuàng)建對(duì)稱密鑰。（http://msdn.microsoft.com/en-us/library/ms188357.aspx）

復(fù)制代碼代碼如下:

 
use DB_Encrypt_Demo 
go 

-- 創(chuàng)建一個(gè)用于加密對(duì)稱密鑰的非對(duì)稱密鑰 
CREATE ASYMMETRIC KEY symDemoKey --名稱 
WITH ALGORITHM = RSA_512 --加密算法 
ENCRYPTION BY PASSWORD = 'TestSYM456!'--密碼 

-- 創(chuàng)建一個(gè)對(duì)稱密鑰 
CREATE SYMMETRIC KEY sym_Demo 
WITH ALGORITHM = TRIPLE_DES 
ENCRYPTION BY ASYMMETRIC KEY symDemoKey 

示例二、查看當(dāng)前數(shù)據(jù)庫(kù)中的對(duì)稱密鑰

使用目錄視圖sys.symmetric_keys(http://msdn.microsoft.com/en-us/library/ms189446.aspx)來(lái)查看。

復(fù)制代碼代碼如下:

 
--查看當(dāng)前數(shù)據(jù)庫(kù)中的非對(duì)稱密鑰 
use DB_Encrypt_Demo 
go 
SELECT name, algorithm_desc FROM sys.symmetric_keys 
----結(jié)果返回 
/* 
name algorithm_desc 
sym_Demo TRIPLE_DES 
*/ 

示例三、修改非對(duì)稱密鑰的加密方式

你可以使用ALTER SYMMETRIC KEY（http://technet.microsoft.com/en-us/library/ms189440.aspx）命令修改對(duì)稱密鑰的加密方式。但執(zhí)行前必須使用OPEN SYMMETRIC KEY(http://msdn.microsoft.com/en-us/library/ms190499.aspx)命令打開(kāi)它。

復(fù)制代碼代碼如下:

 
use DB_Encrypt_Demo 
go 

--先用私鑰密碼打開(kāi)對(duì)稱密鑰 
OPEN SYMMETRIC KEY sym_Demo 
DECRYPTION BY ASYMMETRIC KEY symDemoKey 
WITH PASSWORD = 'TestSYM456!' 

--打開(kāi)之后，先增加密碼加密，取代原密鑰 
ALTER SYMMETRIC KEY sym_Demo 
ADD ENCRYPTION BY PASSWORD = 'newnew!456' 
--再刪除非對(duì)稱密鑰加密 
ALTER SYMMETRIC KEY sym_Demo 
DROP ENCRYPTION BY ASYMMETRIC KEY symDemoKey 
--完成操作后，關(guān)閉對(duì)稱密鑰 
CLOSE SYMMETRIC KEY sym_Demo 

示例四、使用對(duì)稱密鑰對(duì)數(shù)據(jù)進(jìn)行加密和解密。

1、為了使用對(duì)稱密鑰對(duì)數(shù)據(jù)進(jìn)行加密，必須首先打開(kāi)它，然后使用函數(shù)EncryptByKey 加密數(shù)據(jù)。(http://msdn.microsoft.com/zh-cn/library/ms174361.aspx)

2、使用DecryptByKey來(lái)解密使用對(duì)稱密鑰加密的數(shù)據(jù)。注意DecryptByKey不像甩EncryptByKey，無(wú)須使用對(duì)稱密鑰GUID。因此，為了解密，必須打開(kāi)正確的對(duì)稱密鑰會(huì)話，否則會(huì)顯示null。

下面是一個(gè)例子：

復(fù)制代碼代碼如下:

 
/****************************3w@live.cn***********************/ 
USE DB_Encrypt_Demo 
GO 
--創(chuàng)建測(cè)試數(shù)據(jù)表，用于對(duì)稱加密 
CREATE TABLE dbo.PWDQuestion 
(CustomerID int NOT NULL PRIMARY KEY, 
PasswordHintQuestion nvarchar(300) NOT NULL, 
PasswordHintAnswer varbinary(200) NOT NULL) 
GO 
--插入加密數(shù)據(jù) 
OPEN SYMMETRIC KEY sym_Demo 
DECRYPTION BY PASSWORD = 'newnew!456' 
INSERT dbo.PWDQuestion 
(CustomerID, PasswordHintQuestion, PasswordHintAnswer) 
VALUES 
(12, '您出生的醫(yī)院名稱？', 
EncryptByKey(Key_GUID('sym_Demo '), '杭州市一')) 
CLOSE SYMMETRIC KEY sym_Demo 

查看未加密的數(shù)據(jù)：

復(fù)制代碼代碼如下:

 
--解密數(shù)據(jù) 
OPEN SYMMETRIC KEY sym_Demo 
DECRYPTION BY PASSWORD = 'newnew!456' 
SELECT CustomerID,PasswordHintQuestion, 
CAST(DecryptByKey(PasswordHintAnswer) as varchar(200)) PasswordHintAnswer 
FROM dbo.PWDQuestion 
WHERE CustomerID = 12 
--打開(kāi)后切記關(guān)閉?。?！3w@live.cn 
CLOSE SYMMETRIC KEY sym_Demo 

邀月工作室

復(fù)制代碼代碼如下:

 
--不打開(kāi)直接讀取 
SELECT CustomerID,PasswordHintQuestion, 
CAST(DecryptByKey(PasswordHintAnswer) as varchar(200)) PasswordHintAnswer 
FROM dbo.PWDQuestion 
WHERE CustomerID = 12 

至此，好像已經(jīng)大功告成了，別，千萬(wàn)別高興得太早！

這里有個(gè)問(wèn)題，如果惡意用戶不知道CustomerID＝13的PasswordHintAnswer列的真實(shí)值，但知道CustomerID＝14的PasswordHintAnswer列的真實(shí)值,則完全可以通過(guò)惡意替換PasswordHintAnswer列而繞過(guò)加密！！3w@live.cn此時(shí)，我們索性連CustomerID列作為驗(yàn)證列也一起加密，以絕后患 !

注意：加密的驗(yàn)證列也可以由另一個(gè)相關(guān)表的列作為參數(shù)傳入。

看一個(gè)完整的例子：

復(fù)制代碼代碼如下:

 
truncate table dbo.PWDQuestion 
go 

--添加兩個(gè)未加密的行 
INSERT dbo.PWDQuestion 
(CustomerID, PasswordHintQuestion, PasswordHintAnswer) 
select 13, '您出生的醫(yī)院名稱？',cast('浙江婦保院' as varbinary) 
union all 
select 14, '您出生的醫(yī)院名稱？',cast('浙江婦保二院' as varbinary) 


--打開(kāi)對(duì)稱密鑰,連CustomerID列一起加密 
OPEN SYMMETRIC KEY sym_Demo 
DECRYPTION BY PASSWORD = 'newnew!456' 
UPDATE dbo.PWDQuestion 
SET PasswordHintAnswer = 
EncryptByKey(Key_GUID('sym_Demo'), 
PasswordHintAnswer,1,--1表示使用驗(yàn)證器值 
CAST(CustomerID as varbinary)) 
WHERE CustomerID in (13,14) 
--打開(kāi)后切記關(guān)閉?。?！3w@live.cn 
CLOSE SYMMETRIC KEY sym_Demo 


--此時(shí)必須這樣查看原數(shù)據(jù) 
OPEN SYMMETRIC KEY sym_Demo 
DECRYPTION BY PASSWORD = 'newnew!456' 
SELECT CustomerID,PasswordHintQuestion, 
CAST(DecryptByKey(PasswordHintAnswer, 1,--1表示使用驗(yàn)證器值 
CAST(CustomerID as varbinary)) as varchar(200)) PasswordHintAnswer 
FROM dbo.PWDQuestion 
WHERE CustomerID = 13 
--打開(kāi)后切記關(guān)閉?。。?w@live.cn 
CLOSE SYMMETRIC KEY sym_Demo 

惡意替換開(kāi)始：

復(fù)制代碼代碼如下:

 
/********************************************************** 
--我們用剛才的CustomerID = 13的PasswordHintAnswer列值 
--替換CustomerID = 14的PasswordHintAnswer列值， 
--再用剛才讀取14的方法讀取真實(shí)值 
**********************************************************/ 

update dbo.PWDQuestion set PasswordHintAnswer= 
(select PasswordHintAnswer from dbo.PWDQuestion where CustomerID = 14) 
where CustomerID = 13 

此時(shí)，我們?cè)俨榭矗?

復(fù)制代碼代碼如下:

 
OPEN SYMMETRIC KEY sym_Demo 
DECRYPTION BY PASSWORD = 'newnew!456' 
SELECT CustomerID,PasswordHintQuestion, 
CAST(DecryptByKey(PasswordHintAnswer, 1,--1表示使用驗(yàn)證器值 
CAST(CustomerID as varbinary)) as varchar(200)) PasswordHintAnswer, 
PasswordHintAnswer as binaryValue 
FROM dbo.PWDQuestion 
WHERE CustomerID in(13,14) 
--打開(kāi)后切記關(guān)閉！??！3w@live.cn 
CLOSE SYMMETRIC KEY sym_Demo 

邀月工作室