Talks at CCD

We frequently host talks at CCD. At the moment, all our talks will be virtual, but we are eagerly awaiting the time when speakers can visit us and give talks in person. If you are interested in giving a talk, please reach out to us. The typical audience for our talks is quite broad comprising students (UGs, Masters, and PhDs) and faculty members working in diverse areas ranging from cryptography and distributed algorithms. We encourage speakers to take their time to motivate their work to a broader audience without losing their intended depth. For this reason, we typically schedule the talks to last up to an hour and a half.

All our welcome. Please email the coordinator if you would like to receive talk announcements.

Coordinator for Aug - Dec, 2021: Simran Kumari (cs19d401 at


Speaker: Suyash Gupta, UC Davis
Date & Time: Friday, April 30, 2021, at 11 AM.
Link: Sent via email to all CSE affiliates. Email John Augustine if you need the link.

Title: Resilient and Scalable Architecture for Permissioned Blockchain Fabrics


Since the introduction of Bitcoin—the first widespread application driven by blockchains—the interest in the design of blockchain-based applications has increased tremendously. At the core of these blockchain applications are consensus protocols that aim at securely replicating a client request among all replicas, even if some replicas are Byzantine faulty. Unfortunately, modern consensus protocols either yield low throughput or face design limitations.

In this work, we present the design of three consensus protocols that facilitate efficient consensus among the replicas. Our protocols help to scale cons ensus through the principles of phase-reduction, parallelization, and geo-scale clustering while ensuring no compromise in fault-tolerance. Further, we believe that the focus on consensus protocols is only one-side of the story. In specific, we present the design of a well-crafted permissioned blockchain fabric (ResilientDB) that can help even a slow consensus protocol outperform a faster protocol. Our results indicate that it is easy to scale BFT protocols to hundreds of replicas and achieve throughputs of the order 350K txns/s.

Speaker: Zhengzhong Jin, Johns Hopkins University
Date & Time: Friday, July 16, 2021, at 9 AM IST.

Title: Non-interactive Zero-knowledge from Sub-exponential DDH


A non-interactive zero-knowledge (NIZK) proof allows a prover to convince a verifier about the truth of a statement by sending a single message, without revealing any other information. NIZKs are fundamental cryptographic primitives that have many applications, such as CCA-secure cryptosystems, signature schemes, blockchains, and more. We provide the first constructions of non-interactive zero-knowledge and Zap arguments for NP based on the sub-exponential hardness of Decisional Diffie-Hellman against polynomial time adversaries (without use of groups with pairings).

Central to our results, and of independent interest, is a new notion of interactive trapdoor hashing protocols.

Joint work with Abhishek Jain.

Speaker: Ruta Jawale, UIUC
Date & Time: Thursday, July 29, 2021, at 9 AM IST.

Title: SNARGs and PPAD Hardness from Sub-exponential LWE


We construct a succinct non-interactive publicly-verifiable delegation scheme for any logspace uniform circuit under the sub-exponential Learning With Errors (LWE) assumption. For a circuit C : {0, 1}^N -> {0, 1} of size S and depth D, the prover runs in time poly(S), the communication complexity is D polylog(S), and the verifier runs in time (D + N) polylog(S). To obtain this result, we introduce a new cryptographic primitive: lossy correlation-intractable hash functions. We use this primitive to soundly instantiate the Fiat-Shamir transform for a large class of interactive proofs, including the interactive sum-check protocol and the GKR protocol, assuming the sub-exponential hardness of LWE. By relying on the result of Choudhuri et al. (STOC 2019), we also establish the sub-exponential average-case hardness of PPAD, assuming the sub-exponential hardness of LWE.

This is based on a joint work with Yael Tauman Kalai, Dakshita Khurana, and Rachel Zhang.

Speaker: Kartik Nayak, Duke university
Date & Time: Monday, August 9, 2021, at 5 PM IST.

Title: Bringing Synchronous Consensus Closer to Practice


Byzantine Fault Tolerant protocols in the synchronous setting have often been considered impractical due to the strong synchrony assumption. On the flip side, synchronous protocols can be used to tolerate up to one-half Byzantine faults. In this talk, I will explain my journey towards improving synchronous protocols, both in theory and practice.