ETHTID: Deployable Threshold Information Disclosure on Ethereum

We address the Threshold Information Disclosure (TID) problem on Ethereum: An arbitrary number of users commit to the scheduled disclosure of their individual messages recorded on the Ethereum blockchain if and only if all such messages are disclosed. Before a disclosure, only the original sender of each message should know its contents. To accomplish this, we task a small council with executing a distributed generation and threshold sharing of an asymmetric key pair. The public key can be used to encrypt messages which only become readable once the threshold-shared decryption key is reconstructed at a predefined point in time and recorded onchain. With blockchains like Ethereum, it is possible to coordinate such procedures and attach economic stakes to the actions of participating individuals. In this paper, we present ETHTID, an Ethereum smart contract application to coordinate Threshold Information Disclosure. We base our implementation on an existing smart contract, ETHDKG, and optimise functionality and costs to fit the TID use case. While optimising for cost savings, we show that the security of the underlying cryptographic scheme is still maintained. We evaluate how the execution costs depend on the size of the council and the threshold and show that the presented protocol is deployable with a council of more than 200 members with gas savings of 20-40% compared to ETHDKG.