The FBI has made it no secret that it hates Apple and Google's efforts to encrypt files in your smartphones and tablets.

Now court documents have emerged showing just how far the Feds are willing to go to decrypt citizens' data.

The paperwork has shown two cases where federal prosecutors have cited the All Writs Act – which was enacted in 1789 as part of the Judiciary Act – to force companies to decrypt information on gadgets.

The Act, which was signed into law by none other than George Washington and later revised in the 20th century, gives the courts the right to...

issue all writs necessary or appropriate in aid of their respective jurisdictions and agreeable to the usages and principles of law.

That's a pretty broad remit, but the Feds think it's just the thing to force Apple and others to break down privacy protections.

Last month, New York prosecutors successfully persuaded a judge that the ancient law could be used to force an unnamed smartphone manufacturer to help unlock a phone allegedly used in a credit card fraud case. The judge ordered the manufacturer to offer "reasonable technical assistance" to make the phone's contents available.

In a second case, in the northern California federal court, prosecutors specifically named Apple in a similar case using the All Writs Act. Documents obtained by Ars Technica show federal law enforcement sought to get Apple to unlock an iPhone 5S as part of a criminal case.

The court filing states investigators were unwilling to try and open the iPhone for fear of damaging a crucial piece of evidence. They asked the courts to force Apple to give them a hand in safely extracting data from the passcode-protected phone.

It's an interesting legal tactic, but the Feds may find out the hard way that the All Writs Act has its limitation. The argument used by Apple and Google over encryption is that, even if they wanted to help the Feds, they can't do anything about it – because modern iOS and Android encrypts data in a way that only the owner can decrypt. Apple and Google say they don't hold any skeleton keys to devices, although sensitive data may end up in the cloud for the cops to seize.

"The court orders contemplate allowing companies to file an objection and if they can’t do it then Apple and Google would spend real time fighting this," EFF legal fellow Andrew Crocker told The Register.

As for whether or not this law could be used to force smartphone sellers to include a backdoor or spyware for police, or even a front door as the FBI says it wants, Crocker said that such use of the All Writs Act isn't "a settled legal issue," and the EFF would be taking a long, hard look at any attempts to do so. ®