Cryptanalysis and Improvement of a Pairing-Free Certificateless Aggregate Signature in Healthcare Wireless Medical Sensor Networks

The healthcare wireless medical sensor network is gradually changing the traditional mode of medical treatments with the rapid development of Internet of Things. Specifically, patients' healthcare data can be continuously collected by medical sensor nodes and transmitted to the medical specialists for disease monitoring, diagnosis and treatments. Recently, due to its advantages of low computational and communication overheads in a multiuser environment, the certificateless aggregate signature (CLAS) scheme has been adopted to prevent the sensitive healthcare data from being tampered and damaged, thereby ensuring the integrity and authenticity of data. In order to further improve the efficiency of CLAS schemes for the sensor nodes with limited resources, several CLAS schemes without bilinear pairing have been proposed. However, security issues prevent them from being fully applied in the practical scenarios. In this article, we analyze the security of a pairing-free CLAS scheme proposed by Liu et al. [IEEE Internet of Things Journal, vol. 7, no. 6, pp. 5256-5266, 2020] by pointing out that their scheme is insecure against adversaries. After that, we introduce an improved scheme to solve the security vulnerability. The security proofs show that our improved scheme is existentially unforgeable against chosen message attacks under the random oracle model. In addition, the length of the aggregate signature in our proposal does not increase with the growth of the number of users, which greatly reduces the communication cost. Finally, the efficiency of our scheme is illustrated through both performance analyses and comparisons of related work.