Apple appears to have made some changes that make it difficult or impossible to run Siri clones on jailbroken iOS devices other than the iPhone 4S. According to a number of sources, Apple has changed the requirements for establishing a successful connection between Siri and the back-end servers that process most requests. Apple has reportedly added a SetAuthenticationToken command to the connection, which prevents Siri clones on non-iPhone 4S devices from establishing a working connection.

A response was not long in coming, however. Shortly after the problem was identified, reports of a workaround began surfacing. It seems that by using one of several file management tools available in the Cydia app store, users can get Siri back by deleting a file called com.apple.assistant.plist from their phone’s var/mobile/Library/Preferences/.

Apple may well have another response in the works, though. If not, it is likely that the forthcoming iOS 5.1, which will probably be released with the iPad 3, will contain fixes that make it harder to jailbreak.

Late last year Apple released a revision to iOS 5.0.1. While the goal of the revision was to fix a problem some iPhone 4S users were having with their phones not recognizing their SIM card, there was an unintended side effect. The new build of iOS left the iPhone’s file system completely unencrypted, giving developers in the jailbreak community free access to the files that make up Siri. Given its reliance on connections to Apple’s servers, Siri had proven extremely difficult to clone on jailbroken iOS devices other than the iPhone 4S. Just two weeks after the revised version of iOS 5.0.1 was released, however, jailbreak developer Grant Paul (chpwn) announced the release of Spire, a fully functional Siri clone that was available for any jailbroken iOS device running iOS 5. Now Siri was available on the iPhone 4, iPhone 3GS, and even both generations of iPad.

Now it looks like Apple may be getting itself into another battle with jailbreak developers. Apple has traditionally closed the holes in iOS code that make jailbreak possible, forcing jailbreak devs to find new ways to crack the operating system every time. Now it looks like they are going to be doing the same thing with Siri.