iPhone Dev Team has just reported that with iOS 4 or higher, Apple has started putting ‘soft’ SHSH blob checks in the firmware.
This means that like iPhone 4 and iPhone 3GS, if iTunes can’t get the SHSH blobs for iPhone 3G or iPod Touch 2nd generation (due to signing window being closed), the iTunes restore will error out.
According to Dev Team, soft SHSH blob check can be easily bypassed by using Redsn0w(Windows) and PwnageTool(Mac).
Those of you with jailbroken iPhone3G and ipt2G devices may now have noticed Cydia starting to save your SHSH blobs too, just like it does for iPhone3GS, ipt3G and later devices. That’s because starting with 4.0, Apple started putting a “soft” SHSH blob check in the firmware. The SHSH blob check is very real in the sense that if iTunes can’t get your blobs (because the Apple signing window has closed), the iTunes restore will error out. But it’s “soft” in the sense that those devices can always use redsn0w or PwnageTool to get past the error (the bootroms themselves for those devices don’t require blobs to be in the firmware files, unlike the newer bootroms).Furthermore, since the 3.x IPSWs for these devices don’t enforce it, you can always restore to 3.x IPSWs outside of any signing windows.
So, Cydia is doing this to allow you to continue to use iTunes to restore to 4.x on iPhone3G and ipt2g outside of Apple’s signing window without needing to use redsn0w or PwnageTool to get around Apple’s annoying new restriction.
And more over I have been observing on cydia displaying as:
This device has SHSHs on file for iPhone OS:4.0