What Is VDF (Verifiable Delay Function)?
Also known as: Verifiable Delay Function
In short
A VDF (Verifiable Delay Function) is a cryptographic function that requires sequential steps that cannot be parallelized, and therefore a set amount of time, to compute, but whose result can be verified very quickly. It is used for randomness generation and proof of time in blockchains.
The key property of a VDF is that the result cannot be computed before a certain amount of time has passed, no matter how many computers are used, because each step needs the result of the previous step. The party doing the computation produces a short proof along with the result, and anyone can check this proof in a very short time. This asymmetry makes a VDF suitable for cryptographically ordering and delaying events that occur over time.
The most important use of VDFs in blockchains is generating random numbers that cannot be manipulated. A random value built from validators' contributions is open to the party making the last contribution seeing the outcome in advance and steering it in their favor. When this value is passed through a VDF, the result can be learned only a set amount of time after the contributions are complete; thus the possibility of manipulation is largely eliminated. In Ethereum research, this approach has been examined for strengthening RANDAO. The Chia network, for its part, uses VDFs in its consensus as proof of time.
The security of a VDF depends on how much attackers can speed up the computation with specialized hardware. For this reason, practical implementations require that computation speed not differ greatly from one piece of hardware to another, and this area remains an active research topic.
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