Wireless sensor networks (WSNs) are increasingly gaining impact on our daily lives. They are finding a wide range of applications in various domains, such as health-care, environmental monitoring, and so on. In future, WSNs are expected to be integrated into the Internet of Things (IoT). The integrity of the sensed data is of primary importance in WSN and IoT applications. However, WSN platforms always have very limited resources in terms of battery power, computing, and memory. Therefore, it is a key challenge to design an energy-friendly, lightweight digital signature algorithm for WSN platforms. In this paper, we present precomputation methods for unbalanced oil-vinegar (UOV) signature scheme by exploiting the energy-harvesting capabilities of WSN to enhance the performance of UOV signature. In addition, we combine a circulant method with precomputation in the UOV signature to further reduce the energy cost. Meanwhile, the circulant method reduces the size and the memory overhead of the precomputation tuple. This increases the availability of precomputation and greatly enhances the availability of the overflow energy. By integrating the above-mentioned optimization methods, the cost of UOV signature in a WSN node can be reduced by 93%. This greatly enhances the performance of UOV signature, making it feasible for the practical deployment on resource-constrained wireless sensor platforms.