SQL Server中加密是层级的，每一个上层为下提供保护。如图：

实例：
/**
SMK(Service Master Key)在SQL Server安装时生成,由Windows DPAPI(Data Protection API)提供保护
**/

/**创建数据库级别DMK(Database Master Key),受SMK保护**/
create master key encryption by password=N'Passw0rd'
go

/**数据库内的加密对象受DMK保护
支持的对称加密算法:DES | TRIPLE_DES | TRIPLE_DES_3KEY | RC2 | RC4 | RC4_128| DESX | AES_128 | AES_192 | AES_256
非对称加密算法：RSA_512 | RSA_1024 | RSA_2048
注意避免使用RC,DESX类算法,2014之后会删除此功能
**/

--1.创建非对称密钥.

create asymmetric key asyc_key_enc 
with algorithm=RSA_1024 
encryption by password=N'Pass@word' 
go

--2.创建对称密钥.

create symmetric key symc_key_enc 
with algorithm=Triple_DES 
encryption by password=N'Pass@word' 
go

--3.创建证书.证书也可被其它方式保护

create certificate cert_ENC 
with subject='certificate for ENC',expiry_date='20990101' 
go
 

--4.对称密钥可由以上三种方式提供加密保护

--4.1 由非对称密钥加密

create symmetric key symc_key_enc_byAsyc 
with algorithm=AES_128 
encryption by asymmetric key asyc_key_enc 
go
 

--4.2 由对称密钥加密

open symmetric key symc_key_enc 
decryption by password=N'
Pass@word'; 
create symmetric key symc_key_enc_bySymc 
with algorithm = DES 
encryption by symmetric key symc_key_enc 
go

--4.3 由证书加密

create symmetric key symc_key_enc_byCert 
with algorithm =AES_128 
encryption by certificate cert_ENC 
go

/**列级数据加密和解密.MSSQL提供以下4对加密/解密函数对列数据加密
EncryptByCert() 和DecryptByCert()—利用证书对数据进行加密和解密
EncryptByAsymKey() and DecryptByAsymKey()—利用非对称密钥对数据进行加密和解密
EncryptByKey() and DecryptByKey()—利用对称密钥对数据进行加密和解密
EncryptByPassphrase() and DecryptByPassphrase()—利用密码字段产生对称密钥对数据进行加密和解密
注意:被加密和解密的数据,必需是varbinary类型
**/

--以ENCRYPTBYKEY为例，其它的大同小异

--对***号IDN进行加密和解密

create table tb(IDN int,Name varchar(20)); 
insert into tb 
values (1234567,'BigBrother'),(090807001,'SpiderMan'),(3366557,'SuperMan') 
go

--新增列Ency_IDN存储加密数据,使用之前由非对称密钥加密的对称密钥symc_key_enc_byAsyc来加密数据

alter table tb add Ency_IDN varbinary(128); 
go 
open symmetric key symc_key_enc_byAsyc 
decryption by asymmetric key asyc_key_enc 
with password=N'
Pass@word'; 
update tb 
set Ency_IDN=ENCRYPTBYKEY(KEY_GUID('symc_key_enc_byAsyc'),CONVERT(Varbinary,IDN));--加密前要转成varbinary 
close symmetric key symc_key_enc_byAsyc --显式关闭对称密钥 
go
 

--解密被加密的列数据

open symmetric key symc_key_enc_byAsyc 
decryption by asymmetric key asyc_key_enc 
with password=N'
Pass@word'; 
select IDN,Ency_IDN,convert(int,DECRYPTBYKEY(Ency_IDN))as Decr_IDN 
from tb; 
close symmetric key symc_key_enc_byAsyc --显式关闭对称密钥 
go
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