Introduction to Verifiable Delay Functions (VDFs)

Summary: Trail of Bits explains that on-chain randomness drawn from block hashes, difficulty, or timestamps is manipulable by miners, and that verifiable delay functions (VDFs), defined by Boneh et al., impose a sequential computation delay so all inputs are finalized before anyone can compute the output. The post describes three candidate constructions - injective rational maps, and the Pietrzak and Wesolowski repeated-squaring schemes in groups of unknown order - and notes that Chia uses repeated squaring while the Ethereum Foundation is developing a pseudorandom number generator combining RANDAO with VDFs.
Bottom line: The post states that a VDF-based leader selection needs only any honest participant, versus the non-colluding honest majority that verifiable secret-sharing schemes like Ouroboros require - a weaker trust assumption that changes what a protocol can survive. It also warns that generating a group of unknown order without a trusted party remains an open problem for RSA groups, and that ASICs could undermine VDF security guarantees in practice.

Read the original at Trail of Bits Blog ↗