Cassiopeia: Practical On-Chain Witness Encryption

Witness Encryption is a holy grail of cryptography that remains elusive. It asks that a secret is only revealed when a particular computational problem is solved. Modern smart contracts and blockchains make assumptions of “honest majority”, which allow for a social implementation of Witness Encryption. The core idea is to make use of a partially trusted committee to carry out the responsibilities mandated by these functionalities - such as keeping the secret private, and then releasing it publicly after a solution to the computational puzzle is presented. We propose Cassiopeia, a smart contract Witness Encryption scheme (with public witness security) and provide an open source composable implementation that can be utilized as an oracle by others within the broader DeFi ecosystem. We devise a cryptoeconomic scheme to incentivize honest participation, and analyze its security under the honest majority and rational majority settings. We conclude by measuring and optimizing gas costs and illustrating the practicality of our scheme.