Understanding Certificates: for Android Publishers

I want to make sure that my upgrade app has the same certificates as the previous version so that it'll be a free upgrade version for those who bought the earlier version. [This page explains about the steps to signing your apk: http://developer.android.com/guide/publishing/app-signing.html]

I am using Eclipse, which compiles and signs the apk for me. As I create a signed apk, it involves creating a Keystore with alias name, password, validity, etc. Then the dialog box titled, "Destination and key/certificate checks" asks for a destination and name for the apk file, and that's it. I am left with a keystore file and apk file.

Question:
When I make my upgrade version, exactly what needs to be the same to qualify as a new version in Android Market Publish? I know the com.companyname.appname needs to be the same. Does the Keystore alias name, password, validity, etc., need to be identical?

It seems that with this above process, I'm only creating a keystore file and not necessarily two certificates. Is this all that's necessary if I'm using Eclipse? The app signing page seems to indicate so. I don't see any place where I am creating a private key.

Thanks!