Managing Secrets with Consensus Networks: Fairness, Ransomware and Access Control

In this work we investigate the problem of using public consensus networks – exemplified by systems like Ethereum and Bitcoin – to perform cryptographic functionalities that involve the manipulation of secret data, such as cryptographic access control. We consider a hybrid paradigm in which a secure client-side functionality manages cryptographic secrets, while an online consensus network performs public computation. Using this approach, we explore both the constructive and potentially destructive implications of such systems. We first show that this combination allows for the construction of stateful interactive functionalities (including general computation) from a stateless client-side functionality, which can be implemented using inexpensive trusted hardware or even purely cryptographic functionalities such as Witness Encryption. We then describe a number of practical applications that can be achieved today. These include rate limited mandatory logging; strong encrypted backups from weak passwords; enforcing fairness in multi-party computation; and destructive applications such as autonomous ransomware, which allows for payments without an online party.