Prove you computed hash^r(input) for some cryptographic hash function [closed]

What is the most efficient way to prove that a person computed r rounds of some cryptographic hash function (ex. sha256) on an input?. The trivial solution seems to be to show all r hashes, where value_i = hash(value_(i-1)) /forall i <= r, but this seems very space inefficient.

closed as off-topic by D.W.♦Jul 3 '17 at 1:10

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