Some great news for you jailbreakers; Saurik, Cydia’s founder, has recently started caching SHSH blobs for 5.0.1. We have been tipped off about this but we were not sure of this first until we saw 5.0.1 signatures are indeed present.
For those of you who don’t have a clue of SHSH blobs, they are signature files which are verified against Apple servers to ensure the latest firmware is running on the device. The main purpose is to allow users to restore to an older iOS version by downgrading the firmware.
Apple has made it a must that every device that is restored needs to be verified individually by their servers. For example, during a restore, you can see ‘Verifying restore with Apple’ at the top information bar in iTunes.
A partial digest of a firmware file to Apple is uploaded by a response protocol which leads to a decision to go on with the restore or not.
SHSH blobs are cached effectively and this makes the process to be bypassed, verifying restore via Saurik’s servers instead.
This is a perfect time for Cydia starting to cache SHSH blobs since we are near of an iOS 5.0.1 untethered jailbreak which will be released by the Chronic Dev Team after which Apple will attempt to counter this exploit by releasing iOS 5.0.2 (or most probably 5.1).
So in case you mistakenly update to the new version that Apple will release, having these SHSH blobs saved on Cydia helps you to downgrade back to iOS 5.0.1 to get the jailbreak again.
It seems that the wishes of the jailbreakers are coming true at the end of 2011, with an untethered jailbreak coming and multiple vulnerabilties being discovered