CREATE TABLE TBLUser 
(    
    Name             nvarchar(30),     
    Password         varbinary(1000)
)

CREATE master key  ENCRYPTION BY PASSWORD ='passW@ord'

CREATE CERTIFICATE TestCert with SUBJECT = 'Test Certificate'

CREATE SYMMETRIC KEY TestSymmetric WITH ALGORITHM = AES_256 ENCRYPTION BY CERTIFICATE TestCert 

OPEN SYMMETRIC KEY TestSymmetric DECRYPTION BY CERTIFICATE TestCert;
INSERT INTO TBLUser values('张三', ENCRYPTBYKEY(Key_Guid(N'TestSymmetric'), '123456'));
CLOSE SYMMETRIC KEY TestSymmetric;

SELECT * FROM TBLUser

OPEN SYMMETRIC KEY TestSymmetric DECRYPTION BY CERTIFICATE TestCert;
SELECT Name, CAST(DecryptByKey(password) as varchar(100)) Password FROM TBLUser;
CLOSE SYMMETRIC KEY TestSymmetric;