"While certain information may need to stay secret for an investigation to be done properly, some details have to be revealed for accountability to even be possible," says CSAIL graduate student Jonathan Frankle, one of the lead authors of a new paper about the system, which they've dubbed ‘AUDIT’ (Accountability of Unreleased Data for Improved Transparency). "This work is about using modern cryptography to develop creative ways to balance these conflicting issues."
AUDIT is designed around a public ledger on which Government officials share information about data requests. When a judge issues a secret court order or a law enforcement agency secretly requests data from a company, they have to make an iron-clad promise to make the data request public later in the form of what's known as a "cryptographic commitment." If the courts ultimately decide to release the data, the public can rest assured that the correct documents were released in full. If the courts decide not to, then that refusal itself will be made known.
AUDIT can also be used to demonstrate that actions by law-enforcement agencies are consistent with what a court order actually allows. For example, if a court order leads to the FBI going to Amazon to get records about a specific customer, AUDIT can prove that the FBI's request is above board using a cryptographic method called "zero-knowledge proofs." First developed in the 1980s by Goldwasser and other researchers, these proofs counterintuitively make it possible to prove that surveillance is being conducted properly without revealing any specific information about the surveillance.
The team developed its aggregation system using an approach called multi-party computation (MPC), which allows courts to disclose relevant information without actually revealing their internal workings or data to one another. The current state-of-the-art MPC would normally be too slow to run on the data of hundreds of federal judges across the entire court system, so the team took advantage of the court system's natural hierarchy of lower and higher courts to design a particular variant of MPC that would scale efficiently for the federal judiciary.
The team plans to explore what could be done to AUDIT so that it can handle even more complex data requests - specifically, by looking at tweaking the design via software engineering. They also are exploring the possibility of partnering with specific federal judges to develop a prototype for real-world use.