Verifiable Delay Tokens for Privacy-Preserving Time Enforcement

This document specifies a protocol for the issuance and verification of Verifiable Delay Tokens (VDT) that proves that a minimum amount of wall time has elapsed since the issuance of the VDT. The protocol does not rely on trusted or synchronized time sources and instead uses Verifiable Delay Functions (VDFs). The protocol supports time- based access control, anti-abuse and privacy-preserving mechanisms by letting the verifier enforce a waiting period, mitigating the abuse without learning client identity. The protocol ensures unlinkability between token issuance and redemption and does not require the verifier to be aware of the client identifiers, network addresses or any long-lived state. VDTs compose well with the existing Internet protocols such as HTTP-based systems and Oblivious HTTP.