password DECRYPT return null

hi every body i want to EECRYPT and DECRYPT my password and so i use EncryptByPassPhrase and DncryptByPassPhrase before convert the pass value it returns result it works fine but its Encrypt i need to make convert when i make convert it return nothing its works and doesnt return any values ? this this my code

INSERT INTO Tbl_Users

(FirstName, LastName, UserName, [PassWord], Email, DateOfBirthday, PhoneNumber, Mobile, [Address], Gender_id, photoUrl, Squerity_Question_Id, Squerity_answer,IsLocked,WrongLoginAttempt)

VALUES

(@FirstName, @LastName, @UserName,EncryptByPassPhrase('12',@PassWord), @Email, @DateOfBirthday, @PhoneNumber, @Mobile, @Address, @Gender_id, @photoUrl, @Squerity_Question_Id, @Squerity_answer,@IsLocked,@WrongLoginAttempt)

SELECT U_id, FirstName, LastName, UserName,convert(varchar(10), DECRYPTBYPASSPHRASE ('12',password))As password, Email, DateOfBirthday, PhoneNumber, Mobile, [Address], Gender_id, photoUrl, Squerity_Question_Id, Squerity_answer

FROM Tbl_Users

where is the problem!!!!!!!!!!