Paper 2022/783

Augmented Random Oracles

Mark Zhandry, NTT Research, Princeton University
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.

Metadata
Available format(s)
PDF
Category
Foundations
Publication info
A major revision of an IACR publication in CRYPTO 2022
Keywords
random oracle uninstantiability deterministic encryption fiat-shamir cca-security
Contact author(s)
mzhandry @ gmail com
History
2022-06-20: approved
2022-06-17: received
See all versions
Short URL
https://ia.cr/2022/783
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2022/783,
      author = {Mark Zhandry},
      title = {Augmented Random Oracles},
      howpublished = {Cryptology {ePrint} Archive, Paper 2022/783},
      year = {2022},
      url = {https://eprint.iacr.org/2022/783}
}
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