Open Surveillance

Cryptography could keep electronic investigations under control.

Bryan Ford

Democracy rests on the principle that legal processes must be open and public. Laws are created through open deliberation; anyone can read or challenge them; and in enforcing them the government must get a warrant before searching a persons private property. For our increasingly electronic society to remain democratic, this principle of open process must follow us into cyberspace. Unfortunately, it appears to have been lost in translation.

The National Security Agency, formed after World War II to spy on wartime adversaries, has clung to military-grade secrecy while turning its signalsintelligence weapons on us and our allies. While nominally still a foreign intelligence agency, the NSA has become a de facto law enforcement agency by collecting bulk surveillance data within the United States and feeding the data to law enforcement agencies. Other agencies also have secret-surveillance fever. The FBI secretly uses warrantless subpoenas to obtain bulk cell-tower records affecting hundreds of thousands of users at once, whether investigating bank robberies or harmless urban pranks. Police spy on entire neighborhoods with fake cellular base stations known as StingRays and have deliberately obfuscated warrants to conceal their use of the technology.

All this secrecy harms our democracy. But effective surveillance does not require total secrecy. It can follow an openness principle: any surveillance process that collects or handles bulk data or metadata about people who are not specifically targeted by a warrant must be subject to public review and should use strong encryption to safeguard the privacy of the innocent. To gain access to unencrypted surveillance data, law enforcement agencies must identify people whose actions justify closer investigation and then demonstrate probable cause. The details of an investigation need not be public, but the data collection process should bewhat was collected, from whom, and how it was decrypted. This is no different from the way the police traditionally use an open process to obtain physical search warrants without publicly revealing details of their investigation.

Technology that my colleague Joan Feigenbaum and I and our research group have developed could allow law enforcement officials to enact this approach without hampering their work. In fact, it could even enhance it. Modern cryptography could let agencies surgically extract warrant-authorized data about people of interest while guarding the privacy of innocent users. In the case of bank robbers known as the High Country Bandits, the FBI intercepted cell-tower records of 150,000 people to find one criminal who had carried a cell phone to three robbery sites. Using our encrypted search system, the FBI could have found the bandits number without obtaining data on about 149,999 innocent bystanders.

Its better to risk that a few criminals will be slightly better informed than to risk the privacy and trust of everyone.

Bryan Ford is an associate professor of computer science at Yale University.

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Open Surveillance