Abstract: Wireless Sensor Networks (WSN) plays vital role in research field. Secure transmission of data along with efficiency is a critical issue for wireless sensor networks (WSNs). Clustering is an efficient and practical way to enhance the system performance of WSNs. In this project work, we study a secure transmission of data for cluster-based WSNs (CWSNs), where the clusters are formed dynamically and sporadically. We propose two Secure and Efficient data Transmission (SET) protocols for CWSNs, called SET-IBS and SET-IBOOs, by means of the Identity-Based digital Signature (IBS) scheme and the Identity-Based Online/Offline digital Signature (IBOOS) scheme. In SET-IBS, security relies on the hardness of the Diffie-Hellman problem in the pairing area. SET-IBOOS further reduces the computational overhead for protocol security, which is important for WSNs, though its security relies on the hardness of the discrete logarithm problem.