Blockchains have turned out to be a valubale tool in managing digital contracts. By allowing to not only sign messages, but also assuring that no message is omitted, and all clients have the same view on the order in which events happened, blockchains are useful far beyond just managing financial transactions. For this to happen, it is highly necessary to provide intrusion resistant service to manage the blockchain. This service needs to reliably operate also in the event that some servers involved are compromised, even if this compromise has not been detected yet. Using modern cryptography, we can provide a secure blockchain service that even operates reliably if up to a third of all involved servers are actively compromised, and that supports recovery from the compromise once these servers are cleansed, i.e., yields all secrets an attacker may have obtained useless after the recovery.

Selected Publications

Asynchronous Byzantine Agreement

Secure and Efficient Broadcast Protocols

Optimistic Atomic Broadcast