Motivated in part by the Snowden revelations, we address the question of whether intelligence and law-enforcement agencies can gather actionable, relevant information about unknown electronic targets without conducting dragnet surveillance. We formulate principles that we believe effective, lawful surveillance protocols should adhere to in an era of big data and global communication networks. We then focus on intersection of cell-tower dumps, a specific surveillance operation that the FBI has used effectively. As a case study, we present a system that computes such intersections in a privacy-preserving, accountable fashion. Preliminary experiments indicate that such a system could be efficient and usable, suggesting that privacy and accountability need not be barriers to effective intelligence gathering.
This work was supported in part by the National Science Foundation under grant 1016875, the Office of Naval Research under grant N00014-12-1-0478, the Defense Advanced Research Projects Agency (DARPA) and the Air Force Research Laboratory under contract FA8750-13-2-0058, and DARPA and SPAWAR Systems Center Pacific under contract N66001-11-C-4018. The views and conclusions herein are those of the authors and should not be interpreted as necessarily representing the office policies or endorsements, either expressed or implied, of DARPA or the U.S. Government.