Under the Login Screen how to match the Encrypted password with the user input of txtPassword.txt Database SQL Server 2005. Front End VB.NET 2012

We created EncryptPassword column to varbinary(256) under SQL Server 2005 Standard Edition SP1

Following are the code :

CREATE MASTER KEY ENCRYPTION
BY PASSWORD = 'BAuthority'
GO

CREATE CERTIFICATE EncryptTestCert
WITH SUBJECT = 'BAuthority'
GO

CREATE SYMMETRIC KEY TestTableKey
WITH ALGORITHM = TRIPLE_DES ENCRYPTION
BY CERTIFICATE EncryptTestCert
GO

ALTER TABLE MasterPassword
ADD EncryptPassword VARBINARY(256)
GO

Insert Into MasterPassword
(UserName, Password, UserLevel, EncryptPassword)
Values( 'sekar', 'sekar', 'L', EncryptByKey(KEY_GUID('TestTableKey'), 'sekar') )


OPEN SYMMETRIC KEY TestTableKey
DECRYPTION BY CERTIFICATE EncryptTestCert
Select UserName, Password, EncryptPassword, CONVERT(nvarchar(15),DECRYPTBYKEY(EncryptPassword)) AS DecryptPassword
From MasterPassword
Where ( ( UserName = 'sekar' ) and
( CONVERT(nvarchar(15),DECRYPTBYKEY(EncryptPassword)) = 'sekar' ) )

0 rows selected. why ? Any mistake in the above SQL

if we search only with the UserName = 'sekar',  1 row is selected,   CONVERT(nvarchar(15),DECRYPTBYKEY(EncryptPassword)) AS DecryptPassword displays with the Chinese language why, it must display sekar only, why in Chinese language.  Kindly see the screen shot in the attached excel file.

Attached the excel file for your reference.

Thanks.

S.N.Ramkumar.
Workings.xlsx