arXiv subjects

Bhaskar Roberts

Publications and source records attributed to Bhaskar Roberts.

5 recordsLinked to original sources

arXiv2026

Unconditional Certified Randomness without Structure

We obtain a certified randomness protocol in the quantum random oracle model. The protocol is non-interactive and publicly verifiable with a classical verifier, and is based on Yamakawa and Zhandry's proof of quantumness [JACM'24]. We prove unconditional security of this protocol against adversaries making subexponentially-many adaptive quantum queries to the random oracle. Prior work on certified randomness relative to a random oracle additionally assumed the Aaronson--Ambainis conjecture or proved security only against low query-depth adversaries.

quant-ph↗

arXiv2026

Certified Randomness without Structure Against Shallow-Query Adversaries

In a recent breakthrough, Yamakawa and Zhandry (J. ACM 2024) constructed a proof of quantumness in the quantum random oracle model (QROM) in which the quantum prover samples a codeword preimage of a publicly computable function H. They conjectured that given any H, a successful prover must sample their preimage from a high-entropy distribution over possible answers. If true, this would give a certifiable randomness protocol in the quantum random oracle model. As partial evidence for their conjecture, Yamakawa and Zhandry proved the security of their certifiable randomness protocol assuming the Aaronson-Ambainis conjecture. We prove the security of the certifiable randomness protocol of Yamakawa-Zhandry unconditionally, without relying on the unproven Aaronson-Ambainis conjecture, against low query-depth quantum adversaries: specifically, adversaries that make up to o(\log \lambda) adaptive quantum queries to the random oracle.

quant-ph↗

arXiv2026

On Best-Possible One-Time Programs

One-time programs (OTPs) aim to let a user evaluate a program on a single input while revealing nothing else. Classical OTPs require hardware assumptions, and even with quantum information, OTPs for deterministic functionalities remain impossible due to gentle-measurement attacks (Broadbent, Gutoski and Stebila, 2013). While recent works achieve positive results for certain randomized functionalities, the fundamental limits and the strongest achievable security notions remain poorly understood. In this paper, we ask for a "best-possible" OTP that achieves the strongest one-time security achievable by any OTP construction. We first show that a generic best-possible one-time compiler cannot exist, even for classical randomized functionalities (assuming lossy encryption schemes exist). Given this impossibility, we introduce a natural subclass of one-time compilers called "testable one-time program" compilers, which output quantum states augmented with reflection oracles for these program states. We show that best-possible testable OTP compilers are achievable by (1) formulating a generalized Single-Effective-Query (SEQ) simulation security notion for quantum channels and show that SEQ security implies best-possible testable one-time security, and (2) constructing SEQ-secure OTPs for all quantum functionalities in the classical oracle model. This yields the first OTP for arbitrary quantum channels beyond classical randomized functionalities. Finally, we propose stateful quantum indistinguishability obfuscation (stateful quantum iO) -- quantum state obfuscation for stateful quantum programs. We show that (1) stateful quantum iO implies best-possible testable OTPs and (2) stateful quantum iO is also achievable in the classical oracle model. These results identify stateful quantum iO as a promising approach towards best-possible testable OTPs.

cs.CR↗

arXiv2024

Quantum One-Time Programs, Revisited

One-time programs (Goldwasser, Kalai and Rothblum, CRYPTO 2008) are functions that can be run on any single input of a user's choice, but not on a second input. Classically, they are unachievable without trusted hardware, but the destructive nature of quantum measurements seems to provide a quantum path to constructing them. Unfortunately, Broadbent, Gutoski and Stebila showed that even with quantum techniques, a strong notion of one-time programs, similar to ideal obfuscation, cannot be achieved for any non-trivial quantum function. On the positive side, Ben-David and Sattath (Quantum, 2023) showed how to construct a one-time program for a certain (probabilistic) digital signature scheme, under a weaker notion of one-time program security. There is a vast gap between achievable and provably impossible notions of one-time program security, and it is unclear what functionalities are one-time programmable under the achievable notions of security. In this work, we present new, meaningful, yet achievable definitions of one-time program security for probabilistic classical functions. We show how to construct one time programs satisfying these definitions for all functions in the classical oracle model and for constrained pseudorandom functions in the plain model. Finally, we examine the limits of these notions: we show a class of functions which cannot be one-time programmed in the plain model, as well as a class of functions which appears to be highly random given a single query, but whose one-time program form leaks the entire function even in the oracle model.

cs.CR↗

arXiv2021

Franchised Quantum Money

The construction of public key quantum money based on standard cryptographic assumptions is a longstanding open question. Here we introduce franchised quantum money, an alternative form of quantum money that is easier to construct. Franchised quantum money retains the features of a useful quantum money scheme, namely unforgeability and local verification: anyone can verify banknotes without communicating with the bank. In franchised quantum money, every user gets a unique secret verification key, and the scheme is secure against counterfeiting and sabotage, a new security notion that appears in the franchised model. Finally, we construct franchised quantum money and prove security assuming one-way functions.

cs.CR↗