C# wpf Sql Table, encrypted passwords

I am working with a application when user can login in the program by typing their information. Passwords are stored in table as encrypted. But when i try to login using this password it doesn't work.

For encrypting data I use this stored procedure

   ALTER procedure [dbo].[inn]
   @use varchar (50) = null,
   @ins varchar (50) = null

 AS


   INSERT INTO [kole].[dbo].[koll]
       ([Userr]
      ,[ins])


 VALUES
        (@use,
       ((EncryptByPassPhrase('8', @ins)))

And for decrypte I use this stored Procedure

  ALTER procedure [dbo].[sle]
 @Use varchar (50) = null,
 @ins varchar (50) = null

 AS
 SELECT Userr,CONVERT(varchar(50),DECRYPTBYPASSPHRASE ('8',ins)) as Password
FROM [kole].[dbo].[koll]
 where Userr = @Use and ins = @ins

   GO 

In c# I use this code for calling data, and log in into program.

              private void btn_Click(object sender, RoutedEventArgs e)
    {
        SqlConnection conn = new SqlConnection("Server = localhost;Database = kole; Integrated Security = true");

            SqlCommand cmd = new SqlCommand("sle", conn);
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@Userr", txt.Text);
            cmd.Parameters.AddWithValue("@ins", psw.Password);
            conn.Open();
            SqlDataAdapter adapt = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            adapt.Fill(ds);
            conn.Close();
            int count = ds.Tables[0].Rows.Count;

            if (count == 0)
            {
                MessageBox.Show("This user don't exist");
                SystemSounds.Hand.Play();
                txt.Text = "";
                psw.Password = "";

            }
            else if (count == 1)
            {
                MessageBox.Show("Granted!");
                SystemSounds.Asterisk.Play();
                conn.Open();
    }

How can I decrypt the password in correct way , to use for login into program. Thanks