Open, privacy-preserving protocols for lawful surveillance
This addresses the challenge for law-enforcement and intelligence agencies to conduct lawful surveillance without compromising privacy, presenting a practical but incremental solution.
The paper tackles the problem of enabling government surveillance while preserving privacy and accountability, demonstrating that actionable information can be obtained without intruding on innocent parties. Experimental results show that privacy-preserving contact chaining can process 27,000 ciphertexts in under two minutes and pinpoint targets among 150,000 ciphertexts within 10 minutes.
The question of how government agencies can acquire actionable, useful information about legitimate but unknown targets without intruding upon the electronic activity of innocent parties is extremely important. We address this question by providing experimental evidence that actionable, useful information can indeed be obtained in a manner that preserves the privacy of innocent parties and that holds government agencies accountable. In particular, we present practical, privacy-preserving protocols for two operations that law-enforcement and intelligence agencies have used effectively: set intersection and contact chaining. Experiments with our protocols suggest that privacy-preserving contact chaining can perform a 3-hop privacy-preserving graph traversal producing 27,000 ciphertexts in under two minutes. These ciphertexts are usable in turn via privacy-preserving set intersection to pinpoint potential unknown targets within a body of 150,000 total ciphertexts within 10 minutes, without exposing personal information about non-targets.