J"ager: Automated Telephone Call Traceback

Unsolicited telephone calls that facilitate fraud or unlawful telemarketing continue to overwhelm network users and the regulators who prosecute them. The first step in prosecuting phone abuse is traceback -- identifying the call originator. This fundamental investigative task currently requires hours of manual effort per call. In this paper, we introduce J"ager, a distributed secure call traceback system. J"ager can trace a call in a few seconds, even with partial deployment, while cryptographically preserving the privacy of call parties, carrier trade secrets like peers and call volume, and limiting the threat of bulk analysis. We establish definitions and requirements of secure traceback, then develop a suite of protocols that meet these requirements using witness encryption, oblivious pseudorandom functions, and group signatures. We prove these protocols secure in the universal composibility framework. We then demonstrate that J"ager has low compute and bandwidth costs per call, and these costs scale linearly with call volume. J"ager provides an efficient, secure, privacy-preserving system to revolutionize telephone abuse investigation with minimal costs to operators.