Our regular Crypto Café seminars take place every other Tuesday,10 am-10:50 am during the semester. We invite local and international experts on topics in Mathematics and Computer Science related to Cryptography and Information Security.
Come and join us for freshly brewed coffee and interesting conversations on the most exciting topics in cryptography.
Where: SE-43 (Charles E. Schmidt College of Science) - Room 215
https://researchseminars.org/seminar/CryptoCafe
You can catch up on any missed meetings by following the link below:
Fall, 2025, Crypto Cafe Schedule:
Speaker: Arindam Mukherjee, Assistant Professor in Mathematics at A.M. College, Jhalda, India. FLYER
Title: The Representation Technique for Small Max-Norm LWE
Abstract: The Representation Technique, originally introduced by Howgrave-Graham and Joux in the context of the Subset Sum problem, has since become a powerful tool in algorithmic cryptanalysis. It was later adapted for Information Set Decoding (ISD). Currently, the state-of-the-art algorithms to counter subset sum and syndrome decoding problems make use of the representation technique in some form. Recently, May (Crypto 2021) proposed a representation-based attack against small max-norm LWE. This work was later improved in Asiacrypt 2023 and JoC 2024 (https://eprint.iacr.org/2023/243).
In this talk, we will give an overview of the representation technique and its impact on the small max-norm LWE problem.
Bio: Arindam Mukherjee works in public-key cryptanalysis, with a focus on post-quantum hardness assumptions. He received his MSc and PhD in Mathematics from IIT Madras, Chennai, India. He is currently an Assistant Professor in Mathematics at A.M. College, Jhalda, India.
October 28, 2025, 10:00 am Science Building (SE-43), room 215
Speaker: Dr. Sohyun Jeon, Ewha Womans University
Title: LastRings: Lattice-based Scalable Threshold Ring Signatures FLYER
Abstract: This talk presents the first lattice-based threshold ring signature scheme with signature size scaling logarithmically in the size of the ring while supporting arbitrary thresholds. Our construction is also concretely efficient, achieving signature sizes of less than 150kB for ring sizes up to N=4096 (with threshold size T=N/2, say). This is substantially more compact than previous work.
Our approach is inspired by the recent work of Aardal et al. (CRYPTO 2024) on the compact aggregation of Falcon signatures, that uses the LaBRADOR lattice-based SNARKs to combine a collection of Falcon signatures into a single succinct argument of knowledge of those signatures. We proceed in a similar way to obtain compact threshold ring signatures from Falcon, but crucially require that the proof system be zero-knowledge in order to ensure the privacy of signers. Since LaBRADOR is not a zkSNARK, we associate it with a separate (non-succinct) lattice-based zero-knowledge proof system to achieve our desired properties.
Bio: Sohyun Jeon recently completed a PhD at Ewha Womans University in the Republic of Korea. Research interests are lattice-based cryptography. In particular, she is interested in zero-knowledge proofs and their applications
