Two hackers have come up with a Siri port that they say brings all the voice assistant’s functionality to any jailbroken iOS 5 device – legally.

Grant Paul and Ryan Petrich say their Spire installer brings all the iPhone 4S Siri functionality to the jailbroken iPhone 4, iPhone 3Gs,iPod Touch and iPad.

And unlike other Siri ports created in the last few weeks, they say, it’s perfectly legal. “Spire uses a new method to obtain the files necessary for Siri, so it doesn’t have the copyright issues encountered by previous attempts,” says Paul.

It’s not the easiest of solutions, though. Apple still requires authorization to use Siri, so information from an iPhone 4S is still required, and this means using a proxy.

Paul points out that for anyone who already owns an iPhone 4S – or has a friend that does – it’s just a matter of using the phone’s ownauthentification tokens. Otherwise, he says, it may be possible to use Google Chrome’s speech API, hooked up to code that can decode the Siri requests and parse Google’s result.

“Maybe in the future someone will find a way to evade the authorization requirement, but from my position here that’s unlikely,” he says. “Hopefully, however, you’ll be able to figure something out.”

In the longer term, once the iPhone 4S is jailbroken, there shouldn’t be any need for the proxy server, he says.

Spire is available free on Cydia now. Paul warns that it uses about 100MB of data, meaning that a Wifi connection is necessary.