SHSH blobs From Cydia Causes Downgrade Problems(source--absinthejailbreak)

SHSH blobs From Cydia Causes Downgrade Problems - Before iOS 6, downgrading an iDevice with remote blobs saved to Cydia servers was very easy with little hiccups or issues.

However, with the release of iOS 6, this process has taken a different turn largely due to Apple increasing security of its firmware and its signing process and of course as a result of partial blobs saved by Cydia. As Saurik pointed out “TSS (Tatsu Signing Server) data Cydia saved for iOS 6.0-6.1.2 is unusable”

SHSH blobs From Cydia Causes Downgrade Problems

Recently, there had been series of unsuccessfuldowngrade of iOS 6.1.3 to earlier versions of iOS 6 on devices like iPhone 3GS & 4 that are supposed to be easily downgraded.

The problem becomes evident at the tail end of the downgrade process where the device is supposed to boot up, but gets stuck on black screen and doesn’t boot. Some say it usually get stuck in soft DFU loop while some are just dumbfounded by the issue.

Majority of those that have encountered this problem are those that got their SHSH blobs & APTicket directly from Cydia.
while those that used Blobs saved locally with the help of TinyUmbrella & iFaith don’t encounter this problem, questions emerges as to why this is happening.

TinyUmbrella to save SHSH blobs

To answer this question, Saurik, the developer of Cydia shed some light as to why this is happening and has warned that people should stay away from using their iOS 6 SHSH blobs from Cydia to downgrade their devices.

A more detailed explanation of this situation can be found in Saurik’s web page

However, the summary of it all is that Apple have gotten more sophisticated with its signing and authentication process of the signatures used on its firmwares and devices.
Furthermore, Apple have implemented a kind of mechanism that only allow the restoration to most recent firmwares, more like most recent and/or one others before the most recent.

Saurik has stated that all of the APTickets Cydia itself requested from Apple for iOS 6 are useless coupled with incomplete SHSH blobs. Thus when the device tries to boot up, there’s not enough shsh blobs to make that happen since Cydia blobs are incomplete there by causing problems for those that try to restore to a earlier iOS using blobs from Cydia.

Despite all these analysis as to why this problem occur, it has been stated that when SHSH blobs saved locally with the help of iFaith andTinyUmbrella is used, the downgrade process will go on smoothly without issues.

While this issue occur, it is reversible. This you can reverse by restoring to iOS 6.1.3 again and then use locally saved blobs if you have them.

What this immediately translate to is that all users that wish to always want to downgrade their iOS version on their devices should begin to use iFaith or TinyUmbrella to save SHSH blobs locally when Apple is still signing the firmware before another iOS gets released especially for iPhone 3GS & 4 users.

On the part of Saurik, work is being made to perfect this saving of blobs to avoid future occurrence  on supported devices. Also, Redsn0w will be updated soon after the HITB conference to address the soft DFU issue and other minor issues.

This is the conclusion of the whole matter.

• Firstly, do not attempt to downgrade your device with remote SHSH blobs saved to Cydia server so as not to end up with a device in soft DFU loop. Always use iFaith to verify blobs

• Secondly, always use iFaith or TinyUmbrella to save SHSH blobs locally immediately you upgrade to a new iOS when that iOS is still currently being signed by Apple and then use that locally saved blobs to downgrade to it when iOS 6.1.4 or 7.0 shows up.

• Finally, Downgrade of iOS is NOT supported on all iDevices. Its only supported iPhone 3GS, iPhone 4 and iPod touch 4G only

I hope the questions have been laid to rest. Drop your comments as to what you think about this issue.