I deleted my Mac App Store certificates and keys …

Hi!

I messed around with my certificates in the keychain, because I have troubles with it in xCode. The problem is, I accidently deleted also certificates for the Mac App Store. Now every app from the Mac App Store says:

“[name]” is damaged and can’t be opened.

Delete “[name]” and download it again from the App Store.

OK, this hint doesn't help.

Which certificates, keys etc. do I need and where can I get it? (I have a second Mac activated for the Mac App Store but no backup for this Mac.)

Thank you!!

PS: Mac OS X 10.6.8 (Snow Leopard)