Function secret sharing (FSS) has seen many applications in privacy-preserving systems. An important feature in these systems is the ability to enforce access control privately. We formalize this notion and provide several constructions for access control in FSS. We evaluate several applications of access control for FSS, including PIR with access control and faster anonymous communication.

Paper · Slides · Code

Talk given at: IRIF laboratory at the CNRS and University of Paris Cité, IEEE S&P. Mix-nets offer great scalability properties and can be used to instantiate anonymous broadcast (and communication) efficiently. We design and build Trellis, a new mix-net based anonymous broadcast system that offers: (1) concrete efficiency, (2) network robustness in the face of malicious servers, (3) scalability with added servers, and (4) security even when a majority of mix servers are malicious.

Paper · Slides · Code Tor can be significantly slower compared to regular browsing largely due to the way in which Tor routes traffic over the internet. Tor requires routing packets through multiple relays forming a "circuit." Traffic congestions between relays on a Tor circuit can lead to delays, increasing latency, and hindering user experience. ShorTor is an overlay for the Tor network which can help find shorter paths between relays using a trick deployed by major CDNs. ShorTor reduces latency between relays, is incrementally deployable, and minimally impacts the security of Tor.

Paper · Slides · Code How do you find and retrieve similar items (a.k.a. nearest neighbors) from a remote database without revealing what you're looking for? We present Preco, an efficient privacy-preserving approximate nearest neighbor search protocol between a client and a remote database (replicated on two non-colluding servers). Preco takes into consideration the privacy of the client and the database. With Preco, clients can efficiently query for nearest neighbors in the database without the high communication overhead of prior work.

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Talk given at: Berkeley University, IEEE S&P. How do you broadcast high-bandwidth documents (e.g., video leaks) anonymously, even when the entire network is monitored?
We design and build Spectrum, a system for anonymously broadcasting large files over an untrusted network without leaking any metadata; even in the presence of a powerful network adversary.

Paper · Slides · Code

Talk given at: Cornell University, Northeastern University, NSDI.

• Access Control for Function Secret Sharing
  S. Servan-Schreiber, Simon Beyzerov, Eli Yablon, and Hyojae Park
  IEEE Symposium on Security and Privacy (Oakland) 2023.
  
• Trellis: Robust and Scalable Metadata-private Anonymous Broadcast
  S. Langowski, S. Servan-Schreiber, and S. Devadas
  Network and Distributed System Security (NDSS) Symposium 2023.
  
• ShorTor: Improving Tor Network Latency via Multi-hop Overlay Routing
  K. Hogan, S. Servan-Schreiber, Z. Newman, B. Weintraub, C. Nita-Rotaru, and S. Devadas
  IEEE Symposium on Security and Privacy (Oakland) 2022.
  
• Private Approximate Nearest Neighbor Search with Sublinear Communication
  S. Servan-Schreiber, S. Langowski, and S. Devadas
  IEEE Symposium on Security and Privacy (Oakland) 2022.
  
• Spectrum: High-Bandwidth Anonymous Broadcast
  Z. Newman, S. Servan-Schreiber, and S. Devadas
  USENIX Symposium on Networked Systems Design and Implementation (NSDI) 2022.
  
• ProSecCo: Progressive Sequence Mining with Convergence Guarantees
  S. Servan-Schreiber, M. Riondato, and E. Zgraggen
  Knowledge and Information Systems 2019 (journal article),
  IEEE International Conference on Data Mining 2018 (conference paper).
  Best Student Paper runner-up Award