In an increasingly connected world, energy efficiency has become a significant problem. Online electronic transactions are booming based on shopping convenience, fast payments, and lower prices. Electronic trading systems are one of the main sources of energy consumption because the so-called contract signing protocol (CSP) is a crucial part of e-commerce. Therefore, the energy consumption is largely determined by the efficiency of the CSP. To this end, an abuse-free CSP with low-storage TTP is proposed to eliminate the enormous energy-consumption problem originating from the unfit protocol design. This protocol exploits a proxy key scheme and introduces a lightweight TTP storage policy that greatly reduces the TTP burden by integrating symmetric encryption aiming at constructing an energy-efficient electronic transaction ecosystem. Theoretical analysis and comparative analysis show that the storage requirement of TTP is reduced by more than 50% while ensuring fairness, optimism and abuse-freeness in our protocol. Moreover, the exchange steps of our protocol are reduced so that the protocol efficiency is improved. © 2018 Elsevier Inc.