Siri has been the most popular and most desired feature of iPhone 4S. People were disappointed when Apple announced that Siri would not be introduced on earlier devices.
Many hackers made Siri work on iPhone 4 and iPhone 3GS, even if partially. However, the jailbreak tweaks and hacker made stuff that could make it possible could not be distributed publicly due to legal reasons.
However, now it is possible to use Siri on iPhone 4 legally. Apple has made the Siri port legally possible by releasing by releasing a recent revision of iOS 5.0.1. Originally this update was for iPhone 4S and Apple TV. The new update offers wide-open access to system files that were previously encrypted.
Musclenerd, a prominent figure in the world of jailbreaking and hacking, recently tweeted that the iOS 5.0.1 update (released on 15 December 2011) featured decrypted ramdisks. This made it possible to extract the necessary files for a Siri port without infringing on Apple’s copyright. MuscleNerd said, “it’s the first public 4S ipsw where the main filesystem keys are obtainable (due to non-encrypted ramdisks).”
So far, all the methods suggested to make Siri work on devices other than iPhone 4S have either been illegal or impractical. To run Siri properly, you need access to an iPhone 4S unique identifier and that key must be switched out in 24 hours to avoid detection. If thousands of devices start calling on Siri from one 4S identifier, it would be easy for to spot the activity and kill the port.
It is unclear why Apple left such an opening for hackers to exploit. However, iOS 5.1 is coming in near future and Apple might re-encrypt the files. Either decrypted files were a mistake or Apple may have something in mind. Either way, Apple has made it legally possible to use Siri on iPhone 4.
Source: Cult Of Mac