The v2 signature scheme for application bundles on Mac OS X 10.9.5+

Monday, September 08, 2014 | Posted by

Apple has decided to introduce a new signing scheme in the upcoming Mac OS X 10.9.5 maintenance release.

The good news is that the new signature is much better from a security point of view. The utility of the old signature was highly questionable, because it allowed unsigned and modifiable files in the application bundle. An attacker could change the JAR files in the application bundle and the signature of the application bundle would remain valid.

The bad news is that all existing signatures are going to break. Only applications with a v2 signature will be accepted by Gatekeeper starting with Mac OS X 10.9.5. On the upside, the v2 signature is backwards compatible with older versions of Mac OS X. The means that if your application bundle is signed with the new scheme it will work in Mac OS 10.8, 10.9 and 10.10 - and hopefully even with future versions of Mac OS X.

We have implemented v2 signatures in install4j 5.1.13, so you can already create application bundles that will work with the upcoming disruptive releases of Mac OS X.

However, this change may have consequences for your install4j projects:

  • The application bundle that is installed by a "Mac OS X single bundle" installer cannot be signed anymore. The installer installs variable files into the bundle and of course it cannot update the signature of the bundle. Previously all these files did not influence the signature (you can see that this was a bad idea), but now everything in the bundle must be signed. If you really need a signed launcher, you have to switch to the "Mac OS X single bundle" archive.
  •  Info.plist files and .vmoptions files in signed bundles cannot be changed anymore without breaking the signature. If you rely on the validity of the signature of the application bundle, you have to ensure that these files remain untouched. This applies to single bundle and folder archives as well as to the folder installer with signed launchers enabled.

To make the correct decisions, you have to understand that a signature is only required for the file that user downloads from the internet. An installer can install application bundles that are unsigned, because those will not be checked by Gatekeeper.

A signature on an installed application bundle is only required if you need access to restricted services, such as iCloud storage or the notification center. In addition, signed application bundles are treated preferentially in some cases. For example, if the user enables the firewall, unsigned application bundles can only receive incoming connections after the user confirms a question from the firewall.

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