We’ve submitted Longitude 1.6.1 to Cydia and Rock to fix the crash on older jailbreaks.

It turns out the Spirit and JailbreakMe jailbreaks disable the iPhone’s code signing check, whereas older jailbreaks such as redsn0w (even the newest releases of it) and blackra1n do not disable this check.

Combine that with the fact that the latest version of Longitude is a “fat binary” – meaning that the app itself contains two versions: one for older processors, and one optimized for the processors in the iPhone 4 and iPad.  What we didn’t know when we released 1.6 is that fat binaries can’t be signed the same way as non-fat binaries.  We’ve since learned and corrected the issue, hence the release of 1.6.1.

For those of you who don’t know, code signing is something the iPhone does as part of its security architecture.  After a binary (the app) is compiled, what’s known as a checksum is generated using some crazy math operations, and then that checksum is signed and stored as part of the binary.  You might be asking yourself, “what’s the point?”.  There are two reasons to sign applications:  First, to make sure they’re from a legitimate source.  In the iPhone’s case, it’s to ensure only apps that are approved by Apple can run on the phone.  Of course, we see how well that worked..  Secondly, though, it’s to ensure that the application remains unmodified.  If even a single byte is changed, the app’s signature is no longer valid.  This is good to ensure that applications aren’t tampered with, so you can’t, for example, install an app that’s intent is to log into some third party service but instead sends your login information to a malicious hacker.  In other words: code signing is good.