Dynamic threshold ECDSA signature and application to asset custody in blockchain

The centralized exchange is one of the hottest DeFi applications based on blockchain transaction systems. However, depositing user assets to the exchanges brings the security risks of assets misappropriation. Threshold cryptosystem can effectively solve the drawbacks of centralized hosting by assigning the assets authorization to multiple trustees, but the collusion attack generated by malicious trustees is still unavoidable. In this paper, we propose a new dynamic threshold ECDSA signature scheme which is compatible with current blockchain transaction system. It realizes distributed custody of assets in exchanges, and further achieves a dynamic mechanism allowing user join and drop out to resist collusion attacks. Specifically, we formalize the definition of this system architecture and give its construction based on basic cryptography modules such as ECDSA signature, distributed key generation, and distributed computation. Analysis and experiment results show that our scheme holds protocol security and is more efficient than other threshold ECDSA signature schemes when threshold is less than 200, which makes it applicable to the assets custody scenarios of exchanges.