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This paper investigates the Random Oracle Model (ROM) feature known as programmability, which allows security reductions in the ROM to dynamically choose the range points of an ideal hash function. This property is interesting for at least two reasons: first, because of its seeming artificiality (no standard model hash function is known to support such… (More)

Loosely speaking, an obfuscation O of a function f should satisfy two requirements: rstly, using O, it should be possible to evaluate f ; secondly, O should not reveal anything about f that cannot be learnt from oracle access to f alone. Several denitions for obfuscation exist. However, most of them are very hard to satisfy, even when focusing on specic… (More)

We revisit the rate-1 blockcipher based hash functions as first studied by Preneel, Govaerts and Vandewalle (Crypto'93) and later extensively analysed by Black, Rogaway and Shrimpton (Crypto'02). We analyse a further generalization where any pre-and postprocessing is considered. This leads to a clearer understanding of the current classification of rate-1… (More)

This paper describes several speedups and simplifications for XTR. The most important results are new XTR double and single ex-ponentiation methods where the latter requires a cheap precomputation. Both methods are on average more than 60% faster than the old methods, thus more than doubling the speed of the already fast XTR signature applications. An… (More)

We present new techniques for deriving preimage resistance bounds for block cipher based double-block-length, double-call hash functions. We give improved bounds on the preimage security of the three " classical " double-block-length, double-call, block cipher-based compression functions, these being Abreast-DM, Tandem-DM and Hirose's scheme. For Hirose's… (More)

We present a new approach to the design of IND-CCA2 secure hybrid encryption schemes in the standard model. Our approach provides an efficient generic transformation from 1-universal to 2-universal hash proof systems. The transformation involves a randomness extractor based on a 4-wise independent hash function as the key derivation function. Our… (More)

We consider how to build an efficient compression function from a small number of random, non-compressing primitives. Our main goal is to achieve a level of collision resistance as close as possible to the optimal birthday bound. We present a 2n-ton bit compression function based on three independent n-ton bit random functions, each called only once. We… (More)

Although identity based cryptography ooers a number of functional advantages over conventional public key methods, the computational costs are signiicantly greater. The dominant part of this cost is the Tate pairing which, in characteristic three, is best computed using the algorithm of Duursma and Lee. However, in hardware and constrained environments this… (More)