Apple’s celebrated fight with the FBI over the security of its encrypted iPhones has shone the spotlight on an old and obscure federal law from 1789 known as the All Writs Act (AWA).

The AWA is a short little statute, giving federal courts the power to “issue all writs necessary or appropriate in aid of their respective jurisdictions and agreeable to the usages and principles of law.”

The FBI argues that the AWA empowers a court to order Apple to create custom software to circumvent the security on an iPhone possessed by one of the San Bernadino shooting suspects.

This is a piece of Swiss Army knife legislation that the FBI is trying to turn into a giant sword

Passed by the First Congress in 1789, this little law is a piece of Swiss Army knife legislation that the FBI is trying to turn into a giant sword, out of all proportion to what it is supposed to do. But if we want to make sense of the current security and privacy controversy pitting the FBI against the tech giant, it helps to understand what the AWA is and what its limits are.

Back in the summer of 1787 ...

Imagine that you are setting up a democratic government for the first time. You’d want to give the government enough power to govern effectively, but you’d also want to set up limits so that the new government didn’t become a tyranny. This is precisely the problem that the drafters of the US constitution faced when they met in Philadelphia in the summer of 1787.

Their solution was clever and elegant: give the new national government explicit but limited powers to do things like create courts and post offices and regulate commerce, but nothing more. In order to fill in between the lines, the drafters also gave Congress the power to “make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers.”

This meant that Congress wasn’t limited by the strict words of the constitution, but that when it went beyond them (for example, to create a national bank), the powers remained limited.

Two years later, when many of those drafters were sitting in the First Congress, the same problem popped up again. Congress wanted to create courts, and to give those courts powers to order people to do things in order to serve justice. A list of everything a court could order would be long and might miss something, but it also didn’t want to make the powers of courts limitless because of that pesky tyranny problem.

The solution (using the Necessary and Proper Clause) was the AWA: give courts flexible powers to issue “necessary and appropriate” orders. That way, the courts would have the flexibility to do their jobs, but to do them subject to appropriate limits.

Laws like the Necessary and Proper Clause or the AWA thus strike a careful balance: They give the government the power to do its job in a way that is flexible but constrained by law. They are exceptions to the rule that all powers must be spelled out and, as exceptions, they must not be allowed to swallow the rule.

In 1977, the FBI tapped the New York Telephone Company ...

The supreme court recognized as much in 1977, when it decided the New York Telephone Company case.

That case approved an AWA court order under which the FBI could install a “pen register” at the phone company which would log the calls two particular phones suspected of illegal gambling made. It ordered the phone company to give the FBI “all information, facilities and technical assistance” necessary to install the pen registers.

The court also laid out a test to govern future AWA cases so as to preserve its important balance between flexibility and tyranny. In order to be lawful, the company being ordered must (1) be related and not “removed” from the case; (2) the order must not place an unreasonable burden on the company; and (3) the company’s assistance must be necessary.

Other commentators have argued at length about why the government’s demands of Apple are legally unprecedented, unreasonably burdensome to Apple, and threatening to the civil liberties and security of the citizens of our digital democracies.

If the FBI wants new powers to break the security of our digital technologies, let it demand a law from Congress

We would note only that we agree with these arguments, and that the AWA should not be used as a blank cheque that lets the government break the security and privacy on which digital trust depends.

A sensible, safe internet requires that we be able to trust the tech companies with whom we entrust the data of our digital lives. The narrow exception of the AWA should not be allowed to swallow the rule that government power is flexible but limited.

This case is about whose purposes dictate the design our technologies. Should iPhones be built to serve people or law enforcement agencies? Technologies designed to protect us are too important to be gradually undermined by such an open-ended law.

If the FBI needs additional powers, let it ask Congress

There is already a strong argument that the Communications Assistance for Law Enforcement Act (CALEA) already limits the ability of law enforcement agents to dictate design and software configurations.

There is a way forward, and it is one that is contemplated by the same constitution that contains the Necessary and Proper Clause that permitted the enactment of the AWA all those years ago.

The courts in the San Bernadino iPhone case shouldn’t let the FBI twist the AWA into something that it is not. Instead, the issue of how much the government can compel tech companies to break the privacy and security of their users should be dealt with by the political process.

If the FBI wants new powers to break the security of our digital technologies, let it demand a law from Congress. And then we can submit that law to the courts to make sure it is constitutional.

Anything else would be a betrayal of the simple idea that government powers must be limited for the benefit of the civil liberties of the citizens in whose name it serves.