sql server 对称加密例子，很好用

-- 创建对称密钥  
CREATE MASTER KEY ENCRYPTION BY PASSWORD = '输入一个对称密钥';  
  
-- 创建证书  
CREATE CERTIFICATE MyCertificate WITH SUBJECT = '创建一个证书名称';  
  
-- 创建对称密钥的加密密钥  
CREATE SYMMETRIC KEY MySymmetricKey   
    WITH ALGORITHM = AES_128   
    ENCRYPTION BY CERTIFICATE MyCertificate;



	-- 打开对称密钥  
OPEN SYMMETRIC KEY MySymmetricKey   
    DECRYPTION BY CERTIFICATE MyCertificate;  
  
-- 要加密的原始数据  
DECLARE @originalData VARCHAR(100) = 'Hello, World!';  
  
-- 加密数据  
DECLARE @encryptedData VARBINARY(MAX);  
SET @encryptedData = ENCRYPTBYKEY(KEY_GUID('MySymmetricKey'), CAST(@originalData AS VARBINARY(MAX)));  
  
-- 显示加密后的数据  
SELECT @encryptedData AS EncryptedData;  
  
-- 解密数据  
DECLARE @decryptedData VARCHAR(100);  
SET @decryptedData = CAST(DECRYPTBYKEY(@encryptedData) AS VARCHAR(100));  
  
-- 显示解密后的数据  
SELECT @decryptedData AS DecryptedData;  
  
-- 关闭对称密钥  
CLOSE SYMMETRIC KEY MySymmetricKey;