After a short couple year hiatus, DC Area Crypto Day is Back!!

Date: Friday, May 1st
Time: 10:00-4:00 ET
Location:  University of Maryland, Brendan Iribe Center, IRB-5105.
Zoom link: contact kaptchuk at umd dot edu
Parking: Here, for $4 / hour. More information here.
Shuttle: from College Park Metro. Take a left out of the fare gates and climb the stairs. Look for the 104 Shuttle bus (there are signs for it), and exit at the Glenn L. Martin Wind Tunnel stop. Alternatively, the walk is ~20ish minutes
Lunch: We will provide light breakfast and coffee and lunch. If you have particular dietary restrictions, please email kaptchuk at umd dot and we will try our best to accomodate you. The earlier you reach out the better

Schedule (Tentitive):

Time	Speaker/Event
10:00-10:30	Welcome/Light breakfast (provided)
10:30-11:30	Aditya Hegde (JHU)
11:30-12:30	Natalie Lang (UMD)
12:30-2:00	Lunch (provided)
2:00-3:00	Saba Eskandarian (UNC)
3:00-4:00	Herry Eldgridge (JHU)

Speakers:

Aditya Hegde

Title: An Algebraic Approach to Designated-Verifier Batch Arguments without Pairings

Abstract: Batch arguments (BARGs) allow a prover to convince a verifier that a batch of statements all belong to an NP language with a short proof whose size is sublinear in the batch size. In recent years, BARGs have emerged as a foundational cryptographic primitive with many applications to cryptography.

Nearly all prior works on BARGs rely on the heavy machinery of probabilistically checkable proofs (PCPs). A notable exception is the work of Waters and Wu (Crypto’22) who presented a direct, algebraic construction of BARGs using bilinear maps. Unfortunately, it is not known how to emulate this approach from any other standard cryptographic assumption. In particular, this challenge persists even for the relaxed notion of designated-verifier BARGs, where verification requires a private key.

In this work, we present a direct, algebraic construction of designated-verifier BARGs from the Decisional Composite Residuosity (DCR) assumption. Conceptually, our construction can be viewed as an analogue to the Waters-Wu construction in the designated verifier setting, but without the use of bilinear maps.

Based on joint work with Abhishek Jain and Akshayaram Srinivasan.

Natalie Lang

Title: On the Privacy Aspects of Compression

Abstract: In this talk, I will discuss an unexpected aspect of compression: beyond reducing communication and storage costs, it inherently conceals information and can thereby serve as a tool for enhancing privacy and security. I will illustrate this perspective through two examples from different federated learning settings.

Saba Eskandarian

Title: Abuse Reporting Protocols for Private Messaging

Abstract: Users expect the ability to report abuse as a standard feature on private messaging applications. Unfortunately, deployed verifiable abuse reporting schemes are brittle, relying on platform access to user metadata and having the moderator in-the-loop for message delivery. Solutions that remove these restrictions incur multiple orders of magnitude higher performance costs on both the client and the server.

This talk will first explore how to minimize abuse reporting costs for these challenging settings, showing some settings where we can reduce costs to nearly match deployed schemes, and showing fundamental performance barriers in others.

Next, we will focus on the setting of third party moderation, where the moderator is not in the loop for message delivery. Allowing third parties to serve as moderators broadens the tools available to platforms that cannot (or choose not to) deploy a large in-house moderation apparatus. Here we will demonstrate new schemes that extend platforms’ and users’ policy and enforcement options compared to existing approaches while simultaneously lowering performance costs compared to prior work.

This talk is based on joint work with Matthew Gregoire, Margaret Pierce, Gabriel Schell, and Jade Keegan.

Herry Eldgridge

Title: Efficient Privacy-Preserving Blueprints for Threshold Comparison

Abstract: Privacy-Preserving Blueprints (PPBs), introduced by Kohlweiss et al. in in EUROCRYPT 2023, offer a method for balancing user privacy and bad-actor detection in private cryptocurrencies. A PPB scheme allows a user to append a verifiable escrow to their transactions which reveals some identifying information to an authority in the case that the user misbehaved. A natural PPB functionality is for escrows to reveal user information if the user sends an amount of currency over a certain threshold. However, prior works constructing PPBs for such a functionality have severe limitations when it comes to efficiency: escrows are either computationally infeasible to compute, or too large to be plausibly stored on a large-scale distributed ledger. We address these gaps by constructing a space and computation-efficient PPB for threshold comparison, producing escrows under 2kb that can be computed in seconds. The scheme can be instantiated using well-known cryptographic primitives, namely variants of the ElGamal encryption scheme and generic non-interactive zero-knowledge proofs. As an additional contribution, we implement one of the theoretical generic PPB constructions originally proposed by Kohlweiss et al. and find that it performs surprisingly well in practice. For the threshold comparison functionality it requires approximately 14kb escrows, and can be computed in around 12 seconds.