On The Cost Distribution of a Memory Bound Function

Memory Bound Functions have been proposed for fighting spam, resisting Sybil attacks and other purposes. A particular implementation of such functions has been proposed in which the average effort required to generate a proof of effort is set by parameters E and l to E · l. The distribution of effort required to generate an individual proof about this average is fairly broad. When particular uses of these functions are envisaged, the choice of E and l, and the system design surrounding the generation and verification of proofs of effort, need to take the breadth of the distribution into account. We show the distribution for this implementation, discuss the system design issues in the context of two proposed applications, and suggest an improved implementation.