ACAC Seminar Abstract

ACAC Seminar Abstract

ACAC Seminars

ACAC Seminar Abstract

Enhanced Target Collision Resistant Hash Functions Revisited

Speaker: Mohammad Reza Reyhanitabar
Date, Time: Fri, 27 Mar 2009 15:00

Enhanced Target Collision Resistance (eTCR) property for a hash function was put forth by Halevi and Krawczyk in Crypto 2006, in conjunction with the randomized hashing mode that is used to realize such a hash function family. eTCR is a strengthened variant of the well-known TCR (or UOWHF) property for a hash function family, i.e., a dedicated-key hash function. Our contributions are twofold. First, we compare the new eTCR property with the well-known collision resistance (CR) property, where both properties are considered for a dedicated-key hash function. We show there is a separation between the two notions, that is in general eTCR property cannot be claimed to be weaker (or stronger) than CR property for any arbitrary dedicated-key hash function. Second, we consider the problem of eTCR property preserving domain extension. We study several domain extension methods for this purpose, including (Plain, Strengthened, and Prefix-free) Merkle-Damgard, Randomized Hashing (considered in dedicated-key hash setting), Shoup, Enveloped Shoup, XOR Linear Hash (XLH), and Linear Hash (LH) methods. Interestingly, we show that the only eTCR preserving method is a nested variant of LH which has a drawback of having high key expansion factor. Therefore, it is interesting to design a new and efficient eTCR preserving domain extension in the standard model.

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