In today’s world, Internet of Things (IoT) has penetrated every aspect of us. The security of IoT is challenging because of the open nature of wireless communication and limited resources of sensor nodes (SNs). In this paper, we propose an efficient heterogeneous signcryption scheme from IoT to an Internet server, in which the server is in a public key infrastructure (PKI) environment, while the IoT is in a certificateless cryptosystem (CLC) environment. The proposed scheme is briefly referred to as CP-EHSC. CLC can settle the drawbacks of key escrow in identity-based cryptography (IBC) and public key certificate management in PKI. At the same time, PKI is suitable for the server since it has been widely adopted on the Internet. Our proposed scheme can provide security proof in the random oracle model (ROM). Performance analysis shows that the proposed scheme not only achieves great optimization in calculation cost and communication consumption but also makes great progress in total energy consumption. In addition, we illustrate the practical applicability of our proposed scheme by providing a realistic use case scenario.