It looks like Apple is close to aggressively combat the “replay attacks” that have till currently allowed users to use iTunes to revive to previous firmware versions using saved SHSH blobs.
Those of you who are jailbreaking for a minute have in all probability heard us periodically warn you to “save your blobs” for every firmware using either Cydia or TinyUmbrella. Saving your blobs for a given firmware on your specific device permits you to revive *that* device to *that* firmware even when Apple has stopped signing it. That’s all close to amendment.
Starting with the iOS5 beta, the role of the “APTicket” is changing — it’s being employed very similar to the “BBTicket” has continually been used. The LLB and iBoot stages of the boot sequence are being refined to rely on the authenticity of the APTicket, that is uniquely generated at every and each restore (in different words, it doesn’t rely simply on your ECID and firmware version…it changes on every occasion you restore, based mostly partly on a random number). This APTicket authentication can happen at each boot, not simply at restore time. as a result of solely Apple has the crypto keys to properly sign the per-restore APTicket, replayed APTickets are useless.