An upcoming change introduced in the latest Mavericks and Yosemite developers previews will require some developers to re-sign their applications and submit updates to the Mac App Store in order to get around Gatekeeper’s watchful eye. According to a technical note from Apple, any apps built and signed on a version of OS X older than 10.9 will now be flagged by Gatekeeper has not having a valid signature.
For users, this will add an extra layer of annoyance when dealing with certain third-party apps, especially those downloaded from the web rather than through the Mac App Store. Where most developers are now in the habit of signing their apps before making them available, if those developers are still doing so on OS 10.8 or older, their apps will fail to launch on 10.9.5 and Yosemite.
To get around this, developers will need to build their apps on Mavericks and update them with new signatures. Users who end up with an app that no longer wants to run can simply right-click the app and choose “Open” from the contextual menu to bypass Gatekeeper for that application.
Apple has urged developers to update to Mavericks, re-sign, and re-submit any App Store apps built on older versions of OS X to avoid any potential issues, though it’s not quite clear if Apple would really allow so many third-party apps currently available on its store to break, or if it will use some workaround to allow App Store apps with old signatures to keep running until the developer gets them updated properly.
The company notes that apps with updated signatures will still be able to run on older versions of OS X, so there’s no possibility of breaking backwards compatiblity with this change. The only users who will be forced to update their OS will be developers building on outdated systems.