Important: Registration is free but mandatory.
Valid STATE-issued photo ID required.
IMPORTANT: No late registrations will be allowed under any circumstance. NO exceptions.
Registration deadline: Oct 15, 2025, 11:59 PM.

Oct 17, 2025 (Friday) at Schapiro Center, 530 W 120th St, room CEPSR 750 (7th floor).

Program

09:00 – 10:00.	Introduction/Coffee
10:00 – 10:50.	Allison Bishop (Proof Trading and City College, CUNY) Fully Anonymous Secret Sharing
11:00 – 11:50.	Yuval Efron (Columbia University) Good Things Come To Those Who Wait: Dishonest-Majority Coin-Flipping Requires Delay Functions
12:00 – 02:00.	Lunch
02:00 – 02:50.	Surya Mathialagan (NTT) Succinct Obfuscation via Propositional Proofs
03:00 – 03:50.	Nir Bitansky (NYU) Shuffling is Universal: Statistical Additive Randomized Encodings for All Functions

Registration Very important

Registration is free but mandatory.
Registration deadline: Oct 15, 2025, 23:59 (ET).
Only registered participants will be allowed to enter.

Venue

Address: Schapiro Center, 530 W 120th St, room CEPSR 750 (7th floor).

room CEPSR 750 (7th floor)
Valid STATE-issued photo ID required.
IMPORTANT: No late registrations will be allowed under any circumstance. No exceptions.

[Directions]

Organizers

Fabrice Benhamouda (Amazon Web Services)
Daniel Escudero (JP Morgan AlgoCRYPT CoE & AI Research)
Tal Rabin (Amazon Web Services and UPenn)
Mariana Raykova (Google)
with the help and support of Tal Malkin.

Support

NY CryptoDay is sponsored by Google.

Abstracts

• Fully Anonymous Secret Sharing / Allison Bishop (Proof Trading and City College, CUNY)

  In a secret sharing scheme, a dealer can share a secret such that any authorized subset of parties can recover the secret while unauthorized subsets learn nothing about the secret. In this work, we study fully anonymous secret sharing (FASS), a variant which strengthens standard secret sharing by requiring two additional properties. The first property is share anonymity: the shares belonging to any unauthorized set of parties should hide all identifiable information such as party identities and whether or not the shares were generated together. In particular, it suffices that such shares be uniform and independent. The second property is anonymous reconstruction, meaning that the reconstruction algorithm should not need to know the reconstructing set of parties. This is motivated by a recent work of Eldridge et al. [USENIX’24], who demonstrated an application of FASS to stalker detection.

  Authors: Allison Bishop, Matthew Green, Yuval Ishai, Abhishek Jain, and Paul Lou

• Good Things Come To Those Who Wait: Dishonest-Majority Coin-Flipping Requires Delay Functions / Yuval Efron (Columbia University)

  We reconsider Cleve’s famous 1986 impossibility result on coin-flipping without an honest majority. Recently proposed constructions have circumvented this limit by using cryptographic delay functions. We show that this is necessary: a (weak) notion of delay functions is in fact implied by the existence of a protocol circumventing Cleve’s impossibility. However, such delay functions are weaker than those used in existing constructions. We complete our result by showing an equivalence, that these weaker delay functions are also sufficient to construct not just fair dishonest-majority coin-flipping protocols, but also the stronger notion of a distributed randomness beacon

• Succinct Obfuscation via Propositional Proofs / Surya Mathialagan (NTT)

  A central line of inquiry in the study of indistinguishability obfuscation (iO) is minimizing the size of the obfuscation. Current results show how to obfuscate programs represented as Turing machines, where the size of the obfuscation depends only on the input length and not on the machine’s running time. Jain and Jin [FOCS 2022] showed how to further remove this dependency for functionally equivalent programs whose equivalence can be proven in Cook’s theory PV, assuming iO for circuits and LWE.

  In this work we investigate the limits of succinct obfuscation. We focus on programs with large descriptions, where most of the description can be made public while only a portion must remain secret. To capture this setting, we put forth a new notion of fully succinct iO, where the size of the obfuscated program grows only with the size of its secret part—and not with the public part or the input length.

  We give a construction of fully succinct iO whose security, like that of Jain and Jin, is restricted to programs equivalent in Cook’s theory PV. We then show how to bootstrap this construction to achieve full iO security using succinct cryptographic primitives with seemingly weaker functionality: either succinct witness encryption or SNARGs for NP with unique proofs (together with PV proofs of their correctness). Finally, we present applications of fully succinct iO, including high-rate obfuscation and succinct computational secret sharing.

  Based on joint work with Abhishek Jain, Zhengzhong Jin and Omer Paneth.

• Shuffling is Universal: Statistical Additive Randomized Encodings for All Functions / Nir Bitansky (NYU)

  Abstract: The shuffle model is a widely used abstraction for non-interactive anonymous communication. It allows $n$ parties holding private inputs $x_1,\dots,x_n$ to simultaneously send messages to an evaluator, so that the messages are received in a random order. The evaluator can then compute a joint function $f(x_1,\dots,x_n)$, ideally while learning nothing else about the private inputs. The model has become increasingly popular both in cryptography, as an alternative to non-interactive secure computation in trusted setup models, and even more so in differential privacy, as an intermediate between the high-privacy, little-utility {\em local model} and the little-privacy, high-utility {\em central curator model}.

  The main open question in this context is which functions $f$ can be computed in the shuffle model with {\em statistical security.} While general feasibility results were obtained using public-key cryptography, the question of statistical security has remained elusive. The common conjecture has been that even relatively simple functions cannot be computed with statistical security in the shuffle model.

  We refute this conjecture, showing that {\em all} functions can be computed in the shuffle model with statistical security. In particular, any differentially private mechanism in the central curator model can also be realized in the shuffle model with essentially the same utility, and while the evaluator learns nothing beyond the central model result.

  This feasibility result is obtained by constructing a statistically secure {\em additive randomized encoding} (ARE) for any function. An ARE randomly maps individual inputs to group elements whose sum only reveals the function output. Similarly to other types of randomized encoding of functions, our statistical ARE is efficient for functions in $NC^1$ or $NL$. Alternatively, we get computationally secure ARE for all polynomial-time functions using a one-way function. More generally, we can convert any (information-theoretic or computational) “garbling scheme” to an ARE with a constant-factor size overhead.

  Joint work with Saroja Erabelli, Rachit Garg, and Yuval Ishai