4 papers from NTT accepted at TCC2026, the premier international conference on cryptography theory

Four papers from NTT Social Informatics Laboratories have been accepted for TCC 2026 (the 24th Theory of Cryptography Conference), a leading international conference on the theory of cryptography, to be held at New York University in New York City, USA, from November 10 to 13, 2026. This international conference "Construction and conceptualization of theoretical paradigms, approaches, and technologies" is strongly focused. (Affiliations are at the time of submission.)

Abbreviated names of the laboratories:
SI: Social Informatics Labs., NTT, Inc.

■Non-Interactive Black-Box Witness-Indistinguishable Commit-and-Prove via Targeted Hitting-Set Generators

Susumu Kiyoshima (SI)

When important information is handled online, a person may want to hide its contents while later proving that a claim about them is correct. Commit-and-Prove combines these two functions: hiding information and proving a statement about it. In this work, we used a Targeted Hitting-Set Generator, which creates useful candidates for each input, to propose a one-message scheme that does not reveal which evidence was used. We also achieved a black-box construction that does not depend on the internal structure of its components. This result contributes to simpler cryptographic protocols that are easier to deploy.

■Cryptography from Sampling Oracles and LOCC Primitives in the Bounded CRQS Model

Zijing Di (EPFL), Fuyuki Kitagawa (SI), Ryo Nishimaki (SI), Nicholas Spooner (Cornell Univ.), Takashi Yamakawa (SI)

To communicate safely across distances, researchers are studying ways to use previously shared quantum states as a resource. In this work, we considered the Bounded CRQS model, where only a limited number of shared states are available. We combined Sampling Oracles, which supply required information, with basic LOCC components based on local operations and ordinary communication. This enabled commitments, signatures, key agreement, and proofs that reveal no underlying content. We further showed that all communication can remain classical. This result contributes to communication infrastructure that uses limited quantum resources safely.

■Proofs of Quantum Memory

Minki Hhan (KAIST), Tomoyuki Morimae (Kyoto Univ.), Yasuaki Okinaka (Kyoto Univ.), Takashi Yamakawa (SI)

If quantum computers are used as remote services, users will need to check from an ordinary computer whether a device can retain the promised amount of quantum memory for a specified time. In this work, we defined this verification method as Proofs of Quantum Memory. It verifies the amount and retention time of memory using only classical communication. We proposed two constructions with different trade-offs among assumption strength, number of exchanges, and soundness error. This result provides a foundation for trusting and using remote quantum computers.

■CountCrypt: Quantum Cryptography between QCMA and PP

Eli Goldin (New York Univ.), Tomoyuki Morimae (Kyoto Univ.), Saachi Mutreja (Columbia Univ.), Takashi Yamakawa (SI)

Some forms of quantum cryptography can remain secure under weaker computational assumptions than conventional cryptography. However, it has not been clear how much computational difficulty is required for primitives such as key agreement and unclonable quantum money. QCMA and PP are complexity classes that can serve as criteria for classifying the computational hardness required by different cryptographic primitives. In this work, we named the class of cryptographic primitives lying between them CountCrypt and clarified its scope. We also identified a minimal mechanism shared by several cryptographic schemes. This result provides a systematic foundation for understanding the assumptions and limits of quantum cryptography.