Secure data transmission is a critical issue for wireless sensor network (WSNs). Clustering is an effective and practical way to enhance the system performance of WSNs. We propose two Secure and Efficient data Transmission (SET) protocols for CWSNs, called SET-IBS and SET-IBOOS. In SET-IBS, security relies on the hardness of the Dif_e-Hellman problem in the pairing domain. SET-IBOOS further reduces the computational overhead for protocol security, which is crucial for WSNs, while its security relies on the hardness of the discrete logarithm problem. We show the feasibility of the SET-IBS and SET-IBOOS protocols with respect to the security requirements and security analysis against various attacks.