Formalizing human ignorance

  • Authors:
  • Phillip Rogaway

  • Affiliations:
  • Dept. of Computer Science, University of California, Davis, California

  • Venue:
  • VIETCRYPT'06 Proceedings of the First international conference on Cryptology in Vietnam
  • Year:
  • 2006

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Abstract

There is a rarely mentioned foundational problem involving collision-resistant hash-functions: common constructions are keyless, but formal definitions are keyed. The discrepancy stems from the fact that a function H : {0,1}* → {0,1}nalways admits an efficient collision-finding algorithm, it's just that us human beings might be unable to write the program down. We explain a simple way to sidestep this difficulty that avoids having to key our hash functions. The idea is to state theorems in a way that prescribes an explicitly-given reduction, normally a black-box one. We illustrate this approach using well-known examples involving digital signatures, pseudorandom functions, and the Merkle-Damgård construction.