Paper 2022/1204

The Pseudorandom Oracle Model and Ideal Obfuscation

Aayush Jain, Carnegie Mellon University
Huijia Lin, University of Washington
Ji Luo, University of Washington
Daniel Wichs, Northeastern University, NTT Research

We introduce a new idealized model of hash functions, which we refer to as the *pseudorandom oracle* (PrO) model. Intuitively, it allows us to model cryptosystems that use the code of a hash function in a non-black-box way. Formally, we model hash functions via a combination of a pseudorandom function (PRF) family and an ideal oracle. A user can initialize the hash function by choosing a PRF key $k$ and the oracle maps it to a public handle $h$. Given the handle $h$ and some input $x$, the oracle will recover the PRF key $k$ and evaluate the PRF on $x$. A user who chooses the PRF key $k$ therefore has a complete description of the hash function and can use its code in non-black-box constructions, while an adversary, who just gets the handle $h$, only has black-box access to the hash function via the oracle. As our main result, we show how to construct ideal obfuscation in the PrO model, starting from functional encryption (FE), which in turn can be based on well-studied polynomial hardness assumptions. In contrast, we know that ideal obfuscation cannot be instantiated in the basic random oracle model under any assumptions. We believe our result gives a heuristic justification for the following: (1) most natural security goals implied by ideal obfuscation are achievable in the real world; (2) we can construct obfuscation from FE with polynomial security loss. We also discuss how to interpret our result in the PrO model as a construction of ideal obfuscation using simple hardware tokens or as a way to bootstrap ideal obfuscation for PRFs to that for all functions.

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aayushjain1728 @ gmail com
rachel @ cs washington edu
luoji @ cs washington edu
wichs @ ccs neu edu
2022-09-12: approved
2022-09-12: received
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      author = {Aayush Jain and Huijia Lin and Ji Luo and Daniel Wichs},
      title = {The Pseudorandom Oracle Model and Ideal Obfuscation},
      howpublished = {Cryptology ePrint Archive, Paper 2022/1204},
      year = {2022},
      note = {\url{}},
      url = {}
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