iOS 5 beta hobbles OS downgrades, untethered jailbreaks

Those who screw up their iPhones with an unsupported jailbreak—or who have bad luck with their iOS upgrades and want to roll back to an older version—are usually able to make everything right again by downgrading their phone’s OS back to the previous version. That practice appears to be on the endangered list, however, thanks to changes within iOS 5. A post at the Dev-Team Blog indicates that Apple is taking steps to inhibit downgrades to previous versions of iOS, in addition to untethered jailbreaks.

Those who regularly jailbreak their iOS devices are usually familiar with the concept of saving your “blobs.” Users can save their SHSH blobs using a tool such as Cydia or TinyUmbrella before upgrading to a new version of the OS so that they can eventually restore that specific device to that firmware via iTunes.

Thanks to some changes that Apple is making to “APTicket” within iOS 5, however, this may no longer be possible. “The LLB and iBoot stages of the boot sequence are being refined to depend on the authenticity of the APTicket, which is uniquely generated at each and every restore (in other words, it doesn’t depend merely on your ECID and firmware version it changes every time you restore, based partly on a random number),” wrote the team behind many iOS jailbreaks and hacks. “This APTicket authentication will happen at every boot, not just at restore time. Because only Apple has the crypto keys to properly sign the per-restore APTicket, replayed APTickets are useless.”

Those who have already backed up pre-iOS 5 blobs will still be able to restore their phones to them, but only using an older version of iTunes. And jailbreaks will likely remain a part of iPhone culture, but they will probably be limited to tethered jailbreaks—no more wireless jailbreaks for you.

“Although it’s always been just ‘a matter of time’ before Apple started doing this (they’ve always done this with the BBTicket), it’s still a significant move on Apple’s part (and it also dovetails with certain technical requirements of their upcoming [over the air] ‘delta’ updates),” wrote the team.

Indeed, a large tradeoff here is the availability of over the air (OTA) updates as part of iOS 5. iPhone users will no longer have to plug their phones into a computer in order to sync or update the OS, and the updates themselves will only contain the things that have changed since the last upgrade—not the entire OS. In this sense, Apple is less likely to be going out of its way to hobble jailbreakers (though that’s undoubtedly a nice side effect from Apple’s point of view), and instead is merely focusing on what needs to be done in order for the OS to be updated. Since jailbreaks and even self-downgrading have never been supported activities, folks who engage in such practices end up getting the short end of the stick when Apple makes major changes to the OS functionality.

In addition to downgrades and tethered jailbreaks, Apple also appears to be mucking with some iPhone unlocking solutions, as evidenced by the recently released iOS 5 beta 2. A hardware-based unlocking tool called Applenberry’s Gevey SIM unlock was able to unlock iOS devices without any kind of jailbreak, though it did make use of an exploit within the OS in order to do the deed. As noted by AppAdvice (hat tip to a tweet by MuscleNerd), Apple closed the hole as part of the latest beta release, with some speculating that Apple was “under pressure” to take care of these unauthorized modifications before the final release of iOS 5.

It’s worth pointing out that we’re still talking about a beta of an unreleased version of iOS 5—any manner of changes could still take place between now and the final release, which is scheduled for this fall. As noted by the Dev-Team, there are many ways to “combat” Apple’s changes, but “a beta period is really not the time or place to discuss them.”