Abstract
We investigate methods for providing easy-to-check proofs of computational effort. Originally intended for discouraging spam, the concept has wide applicability as a method for controlling denial of service attacks. Dwork, Goldberg, and Naor proposed a specific memory-bound function for this purpose and proved an asymptotically tight amortized lower bound on the number of memory accesses any polynomial time bounded adversary must make. Their function requires a large random table which, crucially, cannot be compressed.
We answer an open question of Dwork et al. by designing a compact representation for the table. The paradox, compressing an incompressible table, is resolved by embedding a time/space tradeoff into the process for constructing the table from its representation.
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Dwork, C., Naor, M., Wee, H. (2005). Pebbling and Proofs of Work. In: Shoup, V. (eds) Advances in Cryptology – CRYPTO 2005. CRYPTO 2005. Lecture Notes in Computer Science, vol 3621. Springer, Berlin, Heidelberg. https://doi.org/10.1007/11535218_3
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DOI: https://doi.org/10.1007/11535218_3
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