Lucrative incentives in grid computing do not only attract honest participants, but also cheaters. To prevent selfish behavior, verification mechanisms are required. Today’s solutions mostly base on redundancy and inherently exhibit a considerable overhead. Often, however, the verification of a result takes much less time than its computation. In this paper we propose a distributed checking scheme that exploits this asymmetry. Our mechanism detects wrong results and excludes cheaters in a distributed manner and hence disburdens the central grid server. We show how the verification scheme is used in an application which aims at breaking the discrete logarithm problem by a parallel implementation of the Pollard-ρ algorithm. Our implementation extends the BOINC server software and is robust to various rational attacks even in the presence of colluders.

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