AbstractSigncryption is a highly efficient approach to achieve simultaneously confidentiality and authentication of message, which is more feasible than the simple combination of encryption and signature. The online/offline cryptography can further enhance the efficiency of signcryption system process without affecting its security. At present, most online/offline signcryptions focus on the ID‐based setting. However, the key escrow problem is inherent in ID‐based cryptography, which is regarded as the main barrier to affect the implementation of system. In this paper, we propose a brand new certificateless online/offline signcryption scheme. We prove the security of our scheme under q‐mBDHI, CDH and q‐CAA assumptions in the random oracle model. The proposed scheme overcomes the key escrow problem in the ID‐based setting. Copyright © 2014 John Wiley & Sons, Ltd.