Robustness for Dishonest Majority in Threshold ECDSA

Abstract: An important application for threshold signature schemes and specifically for ECDSA is decentralized custody over digital assets. The main idea here is for a committee of nodes to jointly control an asset by maintaining a threshold key allowing to move or spend this asset. Decisions on what actions to perform come either from an external control system, or are made via some form of consensus within the group of nodes. Since we cannot assume that all nodes behave honestly in such systems, a property of crucial importance is "robustness" of signing. This means that whenever a decision to sign a message is made, the committee of nodes should succeed in producing a valid signature, despite adversarial behavior of a subset of them. We propose a new dishonest majority threshold ECDSA protocol that offers robustness and does not require choosing a subset of honest signers for a signature to be generated.