research
2025
- In SubmissionATAVISM: Private Originator Tracing in End-to-End Encrypted MessagingArchisman Dutta, Debayan Gupta, and Arup Mondal2025
End-to-end encrypted (E2EE) messaging helps billions of people keep their communications private. However, this makes it easy for bad actors to use these platforms to disseminate illegal content. Law-enforcement authorities across the world have long demanded some kind of exceptional access to (or control over) E2EE messaging, resulting in pushback from civil rights organizations and cryptography experts, who argue that such “backdoors” are bad for a variety of reasons. However, one proposal from the Government of India, The Information Technology (Intermediary Guidelines and Digital Media Ethics Code) Rules, 2021 [Gazette of India, Extra., Pt. II, Sec. 3(i), 25-Feb-2021], proposes something slightly different: tracing the originator of a reported message, where the plaintext and metadata of a message are revealed to law enforcement by a legitimate user. We construct, implement, and benchmark ATAVISM, a solution which achieves private originator tracing, meeting all the requirements of the Indian law while being easily generalizable and preserving practically all aspects of E2EE. We emphasize that our approach does not solve the issue of tying an individual to their device, or of malware. Our scheme is lightweight, realistic, and reveals only the required information: the identity of the originator of a forwarding chain. We test ATAVISM by implementing and benchmarking against prior work, as well as a variant of our protocol with different tradeoffs; we are substantially faster in all cases, and an order of magnitude faster for some functions.