BCD Edition-7
Welcome to the Bengaluru Crypto Day, 7th edition. We will have a day full of exciting topics in cryptography presented by leading researchers.Speakers
Venue
CSA Seminar Hall, Room #104
Schedule
| Time | Speaker | Title |
|---|---|---|
09:55 - 10:00 : Welcome | ||
| 10:00 - 11:00 | Varun Narayanan | Query-Reusable Proof Systems
ABSTRACT: A probabilistically checkable proof (PCP) is a proof that can be verified by a randomized verifier who reads/queries only a few bits from the proof, yet correctly identifies valid or invalid claims with high probability. PCPs and their zero-knowledge variants (ZK PCPs) are central primitives in cryptography. In this talk, we will look at query-reusable proof systems, where a verifier pre-samples its query set (the indices where it chooses to probe the proof) at the outset and reuses it to efficiently verify polynomially many proofs.
The main challenge in this setting is maintaining soundness against a malicious prover who can iteratively submit malformed proofs and use the verifier's binary (accept/reject) feedback to progressively learn the reused query set. This question is motivated in part by attractive features of designated-verifier NIZK (Non-Interactive Zero-Knowledge proofs) that can be obtained by combining symmetric encryption with a query-reusable honest-verifier ZK-PCP.
We show that, under standard complexity-theoretic assumptions, fully query-reusable PCPs and statistical ZK-PCPs are impossible. To bypass this impossibility, we investigate a more refined notion, bounded query-reusability, in which the prover interacts with the verifier over a bounded number of rounds, submitting polynomially many proofs in each round and learning the verifier’s decisions. In this model, we obtain a nearly tight characterization of the number of rounds of query-reusability in terms of the size of the query set.
This talk is based on joint work with Yuval Ishai, Eyal Kushilevitz, Rafail Ostrovsky, and Akash Shah. The only assumed background is basic familiarity with core concepts in complexity theory and cryptography.
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11:00 - 11:30 : Tea/Coffee break | ||
| 11:30 - 12.30 | Debayan Das | Side-Channel Attack Resilient Post-Quantum Crypto Implementation
ABSTRACT: Post-Quantum Cryptography (PQC) has emerged as the most promising alternative to the traditional public key cryptographic protocols. This talk will dive into the need for PQC and compare it against the quantum cryptography protocols. Next, we will investigate the side-channel analysis (SCA) of crypto protocols - understanding it from the basics of power and electromagnetic SCA attacks and its countermeasures. Finally, we will discuss the way forward towards the development of a SCA-resilient PQC processor design.
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12:30 - 14:00 : Lunch break | ||
| 14:00 - 15:00 | Bhavana Kanukurthi | Good, Bad and Rational: A Cryptographer’s Dilemma
Cryptography lays the mathematical foundations of secure communication and is often treated as a perpetual battle between the good guys and the bad guys. In this talk, using auctions as a test-bed, we strive to make a case for deviating from this characterization and for viewing parties as rational agents instead.
Based on joint works with Chaya Ganesh, Shreyas Gupta and Girisha Shankar.
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15:00 - 15:30 : Tea/Coffee break | ||
| 15:30 - 16:30 | Daniel Escudero | Merces: Private Token Transfers via MPC and CoSNARKs
ABSTRACT: We present Merces 1, a confidential token contract that hides user balances and transaction amounts while preserving on-chain verifiability. The core idea is to store secret-shares of balances on a decentralized MPC network, with only hiding commitments posted publicly to a smart contract. Deposits, withdrawals, and transfers are all computed privately in MPC, with the MPC network generating a collaborative SNARK (CoSNARK) to prove that each state transition is valid: concretely, that commitments have been updated correctly and that the sender always has sufficient funds. The result is a system achieving over 300 transactions per second including proof generation, with minimal client-side computation. We discuss the ZK circuit design for deposit, withdrawal, and transfer proofs, the batching strategy that amortizes on-chain verification costs, and the concrete instantiation using Groth16 over BN254 with Poseidon2-based commitments. Finally, we present experimental results and discuss future work.
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