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UID:ac436da6a5946ea3d1474d8dcaf22545-435
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DESCRIPTION:Cryptographic Primitives with Hinting Property
URL;VALUE=URI:https://www.csa.iisc.ac.in/newweb/event/435/cryptographic-primitives-with-hinting-property/
SUMMARY:A hinting pseudorandom generator (PRG) is a potentially stronger variant of PRG with a ``deterministic`` form of circular security with respect to the seed of the PRG (introduced by Koppula and Waters in CRYPTO 2019). Hinting PRGs enable many cryptographic applications, most notably CCA-secure public-key encryption and trapdoor one-way functions. In this talk, I will cover a recent work where we study cryptographic primitives with the hinting property. Our work introduces a novel and conceptually simpler approach for designing hinting PRGs from certain decisional assumptions over cyclic groups or isogeny-based group actions, which enables simpler security proofs and new instantiations from concrete assumptions as compared to the existing approaches for designing such primitives. In this talk, I will present a detailed treatment of this simple approach for constructing hinting PRGs, including a concrete construction and proof from the DDH assumption over cyclic groups. Our work also introduces several extensions of hinting PRGs, such as: (i) a natural extension of the hinting property to weak pseudorandom functions (which we call hinting wPRFs),and (ii) a stronger version of the hinting property (which we call the functional hinting property) that guarantees security even in the presence of hints about functions of the secret seed/key. We show how to instantiate these extensions by building upon our simple approach to realize hinting PRGs, and also demonstrate that these extensions have stronger implications than plain hinting PRGs, particularly in realizing various notions of KDM-secure encryption. Additionally, we study the cryptographic complexity of hinting PRGs and show the first black-box separation between public-key encryption and hinting PRGs via a simple construction of hinting PRGs given only a random oracle (this black-box separation result also extends to hinting wPRFs). The talk will present a high-level overview of these results. Based on a joint work with Navid Alamati (https://eprint.iacr.org/2022/1770, appeared at ASIACRYPT 2022). Some prior background on cryptography will be useful, but not absolutely necessary.
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