Improved Security of a Pairing-Free Certificateless Aggregate Signature in Healthcare Wireless Medical Sensor Networks

Certificateless aggregate signature (CLAS) schemes reduce the trust on the key generation center of identity-based signatures and thus partially address the inherent key escrow issue in identity-based cryptosystems while retaining the advantage of implementation efficiency. In the past few years, a number of new CLAS schemes were proposed to overcome the communicational and computational limitations of sensors and attain integrality, validity, and availability of patients' medical data in healthcare wireless medical sensor networks (HWMSNs). However, many of these schemes do not provide enough security guarantees. In this article, we first review a most recent CLAS scheme for HWMSNs and show that it is insecure for medical applications by presenting attacks due to a type I adversary and a type II adversary. Then, we put forth an improved construction which is provably secure under the CLAS security model in the random oracle model. Our detailed analyses demonstrate that the proposed scheme not only overcomes the security flaws but also has higher implementation efficiency and lower communication cost.