Lately I have noticed a lot of questions related to SHSH-s and the possibility to do downgrade from iOS 6.1.x to lower versions of iOS 6 or even iOS 5, and although I reported a few months ago the details of the changes made by Apple, I will talk about everything again. To begin with, I will tell you that the SHSHs are useless starting with iOS 6 if you have a terminal released after iPhone 4, i.ePad 2, iPad 3, iPhone 4S, iPhone 5, iPad Mini, iPad 4, iPod Touch 5G. On none of these terminals YOU WILL NOT BE ABLE TO DO IT downgrade from iOS 6.1.x to iOS 6.x, or lower versions, except for iPad 2 which allows this NO MORE in case you have saved SHSHs for iOS 5.x and iOS 4.x.
Unfortunately, the Dev Team has not discovered a method to make SHSHs useful on these terminals and at the moment it seems unlikely to discover any method to make them usable. Apple started blocking signing of old versions of iOS on the same night they release a new version, meaning Apple stopped signing SHSHs for iOS 6.1 just an hour after the launch iOS 6.1.2. If in the past Apple did not do this for several days, now it acts extremely quickly and forces users to install only the latest version of iOS.
Unfortunately SHSHs, or blobs saved with redsn0w, prove to be useless for those who don't own an iPhone 3GS or an iPhone 4, and don't try to downgrade via iTunes or redsn0w on other new devices, because you won't succeed and you may have to restore. In conclusion, SHSHs are useless on iOS 6.x if you own an iDevice released after iPhone 4.
