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CREATE SYMMETRIC KEY key1 WITH ALGORITHM=DES
    ENCRYPTION BY PASSWORD='abc$123'
GO

OPEN SYMMETRIC KEY key1    
    DECRYPTION BY PASSWORD='abc$123'

DECLARE @str NVARCHAR(100),@Encrypted VARBINARY(MAX)
SET @str=N'要加密的字串'    
SELECT @Encrypted=ENCRYPTBYKEY(KEY_GUID('key1'),@str)
SELEcT '加密'=@Encrypted ,'解密'=CAST(DECRYPTBYKEY(@Encrypted) AS NVARCHAR(100))
CLOSE SYMMETRIC KEY key1
GO
DROP SYMMETRIC KEY key1
GO