In a second part of the paper, we aim to investigate two recent leakage resilient pseudorandom generators, both from a theoretical and practical point of view. On the one hand, we consider a forward secure generator from ASIACCS 2008 and its similarities with a previous construction by Bellare and Yee. On the other hand, we analyze Pietrzak's block cipher based construction from Eurocrypt 2009. Doing this, we put forward the difficulty of meaningfully restricting the physical leakages and show that this difficulty leads to different drawbacks. It allows us to emphasize the differences between these two designs. First, one construction that we analyze requires strong black box assumptions (i.e. random oracles) - the other one considers unrealistic leakages leading to (possibly useless) performance overheads. Second, one construction considers an adversary able to adaptively choose a leakage function while the second one does not permit this adaptivity. Third, the security proof of the Eurocrypt 2009 construction relies on the assumption that ``only computation leaks'' (or relaxed but related hypotheses) while this assumption is not necessary for the ASIACCS construction. We then discuss the impact of these hypotheses with respect to recent technological advances.
In the third part of the paper, we show that Pietrzak's leakage resilient mode of operation from Eurocrypt 2009 can be broken with a standard DPA if it is re-initialized without sharing new keys. Then, we propose solutions to fix this issue and extend the initial proposal from ASIACCS 2008 in order to rely on more standard cryptographic constructions. We use these alternative designs to illustrate the incompatibility between a fully adaptive selection of the leakage function and the secure initialization of a pseudorandom generator. We also argue that simple pseudorandom functions (e.g. the one of Goldreich, Goldwasser, Micali) can be shown leakage resilient, using the random oracle methodology. We additionally discuss the security vs. performance tradeoff that is inherent to these different schemes. Eventually, we show that the security of the forward secure pseudorandom number generator of Bellare and Yee against side-channel attacks cannot be directly generalized in the standard model. It is an open problem to determine the minimum black box assumptions and restrictions of the leakage function for this purpose.Category / Keywords: implementations. Publication Info: work in progress. Date: received 10 Jul 2009, last revised 13 Mar 2010 Contact author: fstandae at uclouvain be Available format(s): PDF | BibTeX Citation Note: more details are available on: http://www.dice.ucl.ac.be/~fstandae/tsca/ Version: 20100313:145524 (All versions of this report) Discussion forum: Show discussion | Start new discussion