updated 12:55 pm EDT, Mon June 27, 2011
iOS 5 to make downgrading more difficult
Apple will soon make it harder for users to revert their iPhones to older versions of the iOS operating system, the unofficial iPhone Dev Team found. iOS 5 beta reportedly has a different APTicket which will refine the way the phone boots. It will look at an authentic APTicket, which will be generated randomly at every restore function rather than ECID and firmware versions.
This authentication process will happen at every boot and not just when restoring phones. Only Apple will have the crypto keys to properly sign the APTicket and used or replayed APTickets won't work. Only iOS 5 and newer handsets are affected by this change and Apple will have the ability to turn it on or off. Tethered jailbreaks will be possible, such as Geohot's limera1n, and restoring to firmwares before iOS 5 using saved blobs will also be possible. Older iTunes versions will need to be used for this, however.
Apple has been doing a similar thing with the BBTicket and a move like this one has been expected as Apple scales up its security efforts. And as in the past, with time the hacking community may find a workaround to this latest security measure.
The company has often tried to discourage jailbreaks but has usually had to do it through future updates that close the security exploits used for jailbreaks. This has helped deter some but often leaves many holding on to an older version or regressing if they update by mistake. Apple still wouldn't have a way to completely shut down jailbreaks but would leave many users cautious about updating the OS too quickly.