MadS&P Weekly Seminar

Abstract: Threshold signatures protect the signing key by sharing it among a group of signers so that an adversary must corrupt a threshold number of signers to be able to forge signatures. In this talk, I will cover two of our recent results on threshold signatures. First, I will talk about how we design a weighted, non-interactive threshold signature scheme (https://eprint.iacr.org/2023/598). Existing threshold signatures with succinct signatures and constant verification times do not work if signers have different weights. We present a new approach to designing threshold signatures for pairing- and discrete logarithm-based cryptosystems. Our scheme supports arbitrary weight distributions among signers, arbitrary thresholds, and is concretely very efficient. Second, I will talk about the adaptive security of threshold signatures (https://eprint.iacr.org/2023/1553). A popular choice of threshold signature scheme is the BLS threshold signature introduced by Boldyreva (PKC'03). Some attractive properties of Boldyreva's threshold signature are that the signatures are unique and short, the signing process is non-interactive, and the verification process is identical to that of non-threshold BLS. These properties have resulted in its practical adoption in several decentralized systems. However, despite its popularity and wide adoption, up until recently, the Boldyreva scheme has been proven secure only against a static adversary. In this paper, we present the first adaptively secure threshold BLS signature scheme based on standard assumptions while retaining all of its existing properties.
 

Bio: Sourav Das is a Ph.D. candidate at UIUC working with Prof. Ling Ren on applied cryptography and consensus algorithms. He is a recipient of the Chainlink Ph.D. Fellowship, a best paper runner's up at ACM CCS 2021, and the Mavis Future Faculty fellow at UIUC. He received his Bachelor's degree from IIT Delhi, where his thesis “Scaling smart contracts in Proof-of-work Blockchains" won the best undergraduate thesis award in the department.