Egg Freckles

Wed 9/12 SHSH Blobs

With the introduction of the iPhone 5 just hours away, and along with it the expected release of iOS 6, now would be a good time to back up your current iOS devices. iOS 5 introduced the ability to backup using iCloud over WiFi, but for a more expedient restore I recommend making a backup in iTunes as well.¹

Both iCloud and iTunes make a decent backup of your iOS devices, but there is one thing they miss that Apple is not telling you about, SHSH Blobs

SHSH Blobs are a Hash signature system developed by Apple to control manual software downgrades on iOS devices. These blobs control which firmware is restorable and which is not. When Apple wishes to restrict users’ ability to “downgrade” their iOS devices to a prior firmware version, Apple can simply refuse to generate this hash during the downgrade attempt, and the install will fail. Each hash is unique to a specific iOS devices, and once Apple stops signing hashes for a OS / hardware combination it is impossible to install that software unless you have backed up your device’s unique SHSH blob for that OS.

This is a very different system than the controls used on Mac OS X. If you buy a Mac today you will always be able to restore it back to the original operating system it came with.² On iOS once a new operating system comes out, Apple stops signing the hashes for the old operating system. An original iPad running iOS 5.1.1 can only run iOS 5.1.1 unless a newer compatible OS is released by Apple, or if the SHS Blobs for that iPad running a particular OS were saved. Apple will never again sign a hash for iOS 4 on a original iPad, so if you want to go back, and don’t have your SHSH Blobs you are out of luck.

In this day and age of rapid operating system development cycles, with new features being delivered every year, you might ask why someone would want to downgrade their iPad to last year’s OS? The obvious answer is jailbreaking, but there are other considerations as well. Maybe the performance on last year’s OS was better on your device.³ Maybe this year’s OS removed some features you can’t live without.⁴ Maybe you are a developer who needs to test your app on an older operating system⁵, or maybe you are an enthusiast who wants to relive iOS 3⁶. For those people I have one word of advice, TinyUmbrella.

TinyUmbrella is an application for capturing Apple’s signed iOS hashes, and playing back those SHSH Blobs in a way that tricks iTunes into installing an iOS downgrade. If you ever want to go back to iOS 5.1.1 on your current iOS device you have to backup your SHSH Blobs NOW!