1. Traceback for End-to-End Encrypted Messaging 2019 CCS SecureMessaging
    Nirvan Tyagi, Ian Miers and Thomas Ristenpart
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    author = {Tyagi, Nirvan and Miers, Ian and Ristenpart, Thomas},
    title = {Traceback for End-to-End Encrypted Messaging},
    booktitle = {Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Security},
    series = {CCS '19},
    year = {2019},
    isbn = {978-1-4503-6747-9},
    location = {London, United Kingdom},
    pages = {413--430},
    numpages = {18},
    url = {http://doi.acm.org/10.1145/3319535.3354243},
    doi = {10.1145/3319535.3354243},
    acmid = {3354243},
    publisher = {ACM},
    address = {New York, NY, USA},
    keywords = {abuse reporting, end-to-end encrypted messaging, message franking, tracing},

Messaging systems are used to spread misinformation and other malicious content, often with dire consequences. End-to-end encryption improves privacy but hinders content-based moderation and, in particular, obfuscates the original source of malicious content. We introduce the idea of message traceback, a new cryptographic approach that enables platforms to simultaneously provide end-to-end encryption while also being able to track down the source of malicious content reported by users. We formalize functionality and security goals for message traceback, and detail two constructions that allow revealing a chain of forwarded messages (path traceback) or the entire forwarding tree (tree traceback). We implement and evaluate prototypes of our traceback schemes to highlight their practicality, and provide a discussion of deployment considerations.