AES-256 Encryption and Decryption

Try this

CREATE SYMMETRIC KEY SK03  
WITH  
    ALGORITHM = AES_256  
    ENCRYPTION BY PASSWORD = 'abcdefghijklmnopqrstuvwxyzasdefb'; 
go
CREATE TABLE [dbo].[_EncryptionTest](  
    [OriginalValue] [varchar](max) NULL,  
    [Encryptedvalue] [varbinary](max) NULL  
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
go
CREATE PROCEDURE [dbo].[_usp_EncryptionTest]  
    @InputString varchar(MAX),  
    @InputString2 varchar(MAX)  

AS  
BEGIN  
    SET NOCOUNT ON;  

    OPEN SYMMETRIC KEY SK03 DECRYPTION BY PASSWORD='abcdefghijklmnopqrstuvwxyzasdefb'  

    INSERT INTO _EncryptionTest
        (OriginalValue, Encryptedvalue)
    VALUES (
        @InputString
        ,ENCRYPTBYKEY(Key_GUID('SK03'), CONVERT(VARBINARY(max),@InputString2))
        )

    CLOSE SYMMETRIC KEY SK03;

END  
go
EXEC _usp_EncryptionTest 'Spring is Finally Here! Spring is Finally Here!','Spring is Finally Here! Spring is Finally Here!'
go
OPEN SYMMETRIC KEY SK03 DECRYPTION BY PASSWORD='abcdefghijklmnopqrstuvwxyzasdefb'  
SELECT   
    [OriginalValue] ,
    CONVERT(varchar(MAX), DECRYPTBYKEY([EncryptedValue]))
FROM  
    _EncryptionTest  
CLOSE SYMMETRIC KEY SK03;

select * from _EncryptionTest

ref: https://dba.stackexchange.com/questions/167920/sql-aes-256-encryption-and-decryption