CS Colloquium - Privacy-Preserving Accountability Online

CS Colloquium - Privacy-Preserving Accountability Online promotional image


Nirvan Tyagi


Technologies that enable confidential communication and anonymous authentication are important for improving privacy for users of internet services. Unfortunately, encryption and anonymity, while good for privacy, make it hard to hold bad actors accountable for misbehavior. Internet services rely on seeing message content to detect spam and other harmful content; services must also be able to identify users to attribute and respond to abuse complaints. This tension between privacy and accountability leads to one of two suboptimal outcomes: Services require excessive trust in centralized entities to hold users accountable for misbehavior, or services leave themselves and/or their users open to abuse.

In this talk, I will highlight two example applications, end-to-end encrypted messaging and anonymous web browsing, where this tension arises and how gaps in accountability can lead to real-world attacks. I will discuss how I have addressed this tension through the design of new cryptographic protocols that preserve user privacy while also providing mechanisms for holding bad actors accountable. In particular, I will cover new protocols for anonymous blocklisting, one-time-use credentials, and transparent key infrastructure.


Nirvan Tyagi is a PhD candidate in the Department of Computer Science at Cornell University, advised by Tom Ristenpart and based at the NYC Cornell Tech campus. Over the past two years, he has held visiting student appointments at University of Washington and Stanford. His research interests span broadly across computer security, applied cryptography, and systems. Most recently, his focus has been on building systems that provide strong user privacy while also providing appropriate accountability against misbehavior. He is the recipient of an NSF Graduate Research Fellowship, a Facebook Ph.D. Fellowship, and a Digital Life Initiative Doctoral Fellowship. Nirvan received an Early Career Award at CRYPTO 2020 and his work on one-time-use credentials is being standardized by the IETF.

Wednesday, February 1, 2023 4:00pm to 5:00pm
Pappajohn Business Building
21 East Market Street, Iowa City, IA 52245
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Individuals with disabilities are encouraged to attend all University of Iowa–sponsored events. If you are a person with a disability who requires a reasonable accommodation in order to participate in this program, please contact Computer Science Dept. in advance at 319-335-0713 or matthieu-biger@uiowa.edu.