Cryptographic Primitives for Privacy Preserving Protocols

Introduction to Verifiable Delay Functions

VDF’s are functions that require a moderate amount of sequential computation to evaluate, but once a solution is found, it is easy for anyone to verify that it is correct. Think of VDF’s as a time delay imposed on the output of some pseudorandom generator. This delay prevents malicious actors from influencing the output of the pseudorandom generator, since all inputs will be finalized before anyone can finish computing the VDF.

When used for leader selection, VDF’s offer a substantial improvement over verifiable random functions. Instead of requiring a non-colluding honest majority, VDF-based leader selection only requires the presence of any honest participant. This added robustness is due to the fact that no amount of parallelism will speed up the VDF, and any non-malicious actor can easily verify anyone else’s claimed VDF output is accurate.