Byzantine quorum systems (BQSs) provide attack-resilient storage services over asynchronous channels and tolerate f servers’ Byzantine failures. COCA (Cornell online certification authority) and CODEX (COrnell Data EXchange) have designed a server protocol to implement BQSs threshold signature schemes (TSS-BQSs), which can execute proactive recovery, conveniently, and can simplify the key management and communication of clients. Under the same system model and channel assumptions, a new server protocol that satisfies the security requirements of TSS-BQS is proposed. The proposed protocol involves less rounds of communication and performs better than that of COCA/CODEX in the case of concurrent read-write operations.