Paper 2020/638

Delay Encryption

Jeffrey Burdges and Luca De Feo

Abstract

We introduce a new primitive named Delay Encryption, and give an efficient instantation based on isogenies of supersingular curves and pairings. Delay Encryption is related to Time-lock Puzzles and Verifiable Delay Functions, and can be roughly described as ``time-lock identity based encryption''. It has several applications in distributed protocols, such as sealed bid Vickrey auctions and electronic voting. We give an instantiation of Delay Encryption by modifying Boneh and Frankiln's IBE scheme, where we replace the master secret key by a long chain of isogenies, as in the isogeny VDF of De Feo, Masson, Petit and Sanso. Similarly to the isogeny-based VDF, our Delay Encryption requires a trusted setup before parameters can be safely used; our trusted setup is identical to that of the VDF, thus the same parameters can be generated once and shared for many executions of both protocols, with possibly different delay parameters. We also discuss several topics around delay protocols based on isogenies that were left untreated by De Feo et al., namely: distributed trusted setup, watermarking, and implementation issues.