Constructions for Quantum Indistinguishability Obfuscation

TL;DR

This paper introduces new definitions and constructions for quantum indistinguishability obfuscation, providing schemes that are computationally and statistically secure under different conditions, advancing quantum cryptography.

Contribution

It presents two novel definitions for quantum indistinguishability obfuscation and provides efficient schemes with security guarantees for specific classes of quantum circuits.

Findings

A computationally-secure scheme for qiO with exponential size in non-Clifford T gates.

A statistically-secure qiOD scheme for circuits close to the kth level of the Gottesman-Chuang hierarchy.

Efficiency depends on the number of T gates and the hierarchy level k, respectively.

Abstract

An indistinguishability obfuscator is a probabilistic polynomial-time algorithm that takes a circuit as input and outputs a new circuit that has the same functionality as the input circuit, such that for any two circuits of the same size that compute the same function, the outputs of the indistinguishability obfuscator are indistinguishable. Here, we study schemes for indistinguishability obfuscation for quantum circuits. We present two definitions for indistinguishability obfuscation: in our first definition (qiO) the outputs of the obfuscator are required to be indistinguishable if the input circuits are perfectly equivalent, while in our second definition (qiOD), the outputs are required to be indistinguishable as long as the input circuits are approximately equivalent with respect to a pseudo-distance D. Our main results provide (1) a computationally-secure scheme for qiO where the size of the output of the obfuscator is exponential in the number of non-Clifford (T gates), which means that the construction is efficient as long as the number of T gates is logarithmic in the circuit size and (2)a statistically-secure qiOD, for circuits that are close to the kth level of the Gottesman-Chuang hierarchy (with respect to D); this construction is efficient as long as k is small and fixed.