# Quantum LLL with an application to mersenne number cryptosystems

Tiepelt, Marcel; Szepieniec, A.

##### Abstract:
In this work we analyze the impact of translating the well-known LLL algorithm for lattice reduction into the quantum setting. We present the first (to the best of our knowledge) quantum circuit representation of a lattice reduction algorithm in the form of explicit quantum circuits implementing the textbook LLL algorithm. Our analysis identifies a set of challenges arising from constructing reversible lattice reduction as well as solutions to these challenges. We give a detailed resource estimate with the Toffoli gate count and the number of logical qubits as complexity metrics.

As an application of the previous, we attack Mersenne number cryptosystems by Groverizing an attack due to Beunardeau et al. that uses LLL as a subprocedure. While Grover’s quantum algorithm promises a quadratic speedup over exhaustive search given access to a oracle that distinguishes solutions from non-solutions, we show that in our case, realizing the oracle comes at the cost of a large number of qubits. When an adversary translates the attack by Beunardeau et al. into the quantum setting, the overhead of the quantum LLL circuit may be as large as 2$^{52}$ qubits for the text-book implementation and 2$^{33}$ for a floating-point variant.

 Zugehörige Institution(en) am KIT Institut für Theoretische Informatik (ITI) Publikationstyp Forschungsbericht/Preprint Publikationsjahr 2019 Sprache Englisch Identifikator KITopen-ID: 1000100596 Umfang 20 S. Externe Relationen Abstract/Volltext Schlagwörter LLL; lattice reduction; quantum circuit; Grover's algorithm; Mersenne number cryptosystems Relationen in KITopen Verweist aufQuantum LLL with an application to mersenne number cryptosystems. Tiepelt, Marcel; Szepieniec, A. (2019) Proceedingsbeitrag (1000100180)
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