International Association for Cryptologic Research

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Paper: Augmented Random Oracles

Authors:
Mark Zhandry , NTT Research & Princeton University
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Conference: CRYPTO 2022
Abstract: We propose a new paradigm for justifying the security of random oracle-based protocols, which we call the Augmented Random Oracle Model (AROM). We show that the AROM captures a wide range of important random oracle impossibility results. Thus a proof in the AROM implies some resiliency to such impossibilities. We then consider three ROM transforms which are subject to impossibilities: Fiat-Shamir (FS), Fujisaki-Okamoto (FO), and Encrypt-with-Hash (EwH). We show in each case how to obtain security in the AROM by strengthening the building blocks or modifying the transform. Along the way, we give a couple other results. We improve the assumptions needed for the FO and EwH impossibilities from indistinguishability obfuscation to circularly secure LWE; we argue that our AROM still captures this improved impossibility. We also demonstrate that there is no ``best possible'' hash function, by giving a pair of security properties, both of which can be instantiated in the standard model separately, which cannot be simultaneously satisfied by a single hash function.
BibTeX
@inproceedings{crypto-2022-32204,
  title={Augmented Random Oracles},
  publisher={Springer-Verlag},
  author={Mark Zhandry},
  year=2022
}