I am using Urban airship in my application for push notification. So, I need to download the push SSL certificate from Apple developer portal. After downloading, I added tha
Apple do not store the private key you used to create your certificates. You need to already have a copy of it on your machine.
It sounds as if perhaps either somebody else requested the push certificate you're trying to download, or you requested it on another machine. If you can't find the private key you will need to create a new certificate request and upload it via the developer portal.