Privacy-Preserving Lawful Contact Chaining

How can government agencies acquire actionable, useful information about legitimate targets, while preserving the privacy of innocent parties and holding government agencies accountable? Towards understanding this crucial issue, we present the first privacy-preserving protocol for contact chaining, an operation that law-enforcement and intelligence agencies have used effectively. Our experiments suggest that a three-hop, privacy-preserving graph traversal producing 27,000 ciphertexts can be done in under two minutes.