Cost-function

§5.8632 — A cost-function is time-like, or asymmetric. It has the synthetic a priori characteristic, essential to cryptography, of being difficult to discover but easy to check. Back states that it “should be efficiently verifiable, but parameterisably expensive to compute.” The combination defines (valid) work. Concretely, work measures applied computational power. It has the game-theoretic meaning of commitment. While deterministic cost-functions are possible, those adopted by hashcash and subsequently Bitcoin are probabilistic, producing tokens based on the performance tested set by particularly arduous (trial-and-error) exercises, precluding short-cuts.[5]