Timelock Encryption: an Overview and Retrospective

Abstract. This talk presents an overview of timelock encryption (TLE), a cryptographic primitive which secures messages until some point in the future specified during encryption. We review definitions, motivations, applications, and discuss trade offs between two popular timelocking techniques: puzzle-based and authority-based. We then present an authority-based TLE from the identity-based encryption (IBE) scheme of Boneh and Franklin, which is in turn constructed from BLS signatures. Our instantiation leverages threshold BLS to replace the trusted IBE authority with a network of parties, each of whom is potentially malicious. The accompanying implementation is built upon the League of Entropy, a threshold network that acts as our decentralized authority via its public randomness beacon service. The details of this TLE construction and implementation are provided. Finally, in retrospect, we discuss the practical challenges of this implementation and address relevant standardization efforts. We also briefly mention our ongoing work to efficiently boost the applicability of this TLE scheme.

Joint work with Nicolas Gailly (Lagrange Labs)

Suggested readings: ia.cr/2023/189