Cryptology ePrint Archive: Report 2010/428

Random Oracles in a Quantum World

Dan Boneh and Özgür Dagdelen and Marc Fischlin and Anja Lehmann and Christian Schaffner and Mark Zhandry

Abstract: The interest in post-quantum cryptography - classical systems that remain secure in the presence of a quantum adversary - has generated elegant proposals for new cryptosystems. Some of these systems are set in the random oracle model and are proven secure relative to adversaries that have classical access to the random oracle. We argue that to prove post-quantum security one needs to prove security in the quantum-accessible random oracle model where the adversary can query the random oracle with quantum state. We begin by separating the classical and quantum-accessible random oracle models by presenting a scheme that is secure when the adversary is given classical access to the random oracle, but is insecure when the adversary can make quantum oracle queries. We then set out to develop generic conditions under which a classical random oracle proof implies security in the quantum-accessible random oracle model. We introduce the concept of a history-free reduction which is a category of classical random oracle reductions that basically determine oracle answers independently of the history of previous queries, and we prove that such reductions imply security in the quantum model. We then show that certain post-quantum proposals, including ones based on lattices, can be proven secure using history-free reductions and are therefore postquantum secure. We conclude with a rich set of open problems in this area.

Category / Keywords: Quantum Random Oracle, Signatures, Encryption

Date: received 2 Aug 2010, last revised 20 Sep 2011

Contact author: anj at zurich ibm com

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Version: 20110920:164913 (All versions of this report)

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