My old Macworld colleague Rob Griffiths explains why some well-known Mac apps recently stopped launching:
[1Password, PDFpenPro, and Soulver] contained an expired code signing certificate. That expired certificate prevented the apps from launching, though no developer would have expected that, based on Apple’s own documentation. And an expired code signing certificate can’t just be renewed to extend its expiration date (like you would a driver’s license); it needs to be replaced with a new non-expired certificate, which requires distributing an update to the app.
As you might expect, Rob dives deep with the details. There’s also an Agile Bits blog post on the subject. (It sounds like Apple’s documentation for this process may be incomplete or wrong and could use an update.)