The official release of iOS 7, Apple's new mobile operating system, has been live for less than a week, and with luck you're enjoying everything the new software has to offer. Because if you've upgraded your older iPhone, you're pretty much stuck with it now.
You Can Upgrade Anytime You Like, But You Can Never Leave
iOS hacker Steven De Franco noted on Twitter and his blog, where he goes by iH8sn0w, that Apple has stopped "signing" older versions of iOS—the ones that you'd want to install on your devices to replace iOS 7. For some time, Apple has created encrypted digital "signatures" linked to specific versions of iOS; without a signature, the operating system won't install.
Looks like Apple is finally starting to stop signing 6.1.3/6.1.4.— iH8sn0w (@iH8sn0w) September 21, 2013
That would effectively kill any chance of downgrading iOS 7 to iOS 6.1.4 (the version that will run on the iPhone 5) or iOS 6.1.3 (for the iPhone 4S and iPod Touch 5).
Where That Leaves You
If you haven't upgraded to iOS 7, you should be fine. And if you downgraded before this weekend—say, after trying out the iOS 7 beta—you're fine. Apple's change won't affect iPhones or iPads that are already running iOS 6. But if you're on iOS 7 now, reverting back could prove daunting—perhaps even impossible—depending on your circumstances.
Let's start with your reason for downgrading. If you want to prepare for an expected tool that "jailbreaks" iOS 6.1.4, removing obstacles Apple has placed to installation of certain kinds of software, there may be a loophole you can exploit if you have an iPhone 4 and you've jailbroken it before.
If you're an experienced jailbreaker, you may well have previously saved your "SHSH blobs"—a technical term for the saved signatures used for verifying that a version of iOS can run on a particular device. If so, those saved signatures might work now to greenlight a downgrade back to iOS 6. But it's not guaranteed to work, and it only applies to the iPhone 4, which has an older processor. (The security routines in the processor may make a difference.) iH8sn0w confirms that this is the only iOS 7-compatible device that can be downgraded.
But if you've got a newer device, or if you want to downgrade just because you're not a fan of iOS 7's look, you may be out of luck.
If you have iOS 7 running on a device with an A5 or newer chip—like the iPhone 4S, iPhone 5, any iPad or the iPod touch 5G—then you may have to settle in and embrace the new OS. At least for the moment, there doesn't seem to be another choice.
And if you really hate iOS 7, until jailbreakers come up with a software solution, you may be left with an extreme option—like buying a used device with iOS 6 installed. There's already a category for such devices on eBay.
I reached out to Apple for comment on this, and will update this post if I hear back.
Feature image screencapped from YouTube video by TechRax