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 …

Recently, Zhan et al. presented a pairing-free certificateless aggregation signature scheme
(ZH-CLAS) to address security issues in healthcare wireless medical sensor networks
(HWMSNs) and proved that their scheme is secure against adaptive chosen message
attacks. In this article, we analyze the security of the ZH-CLAS scheme by utilizing two types
of concrete attacks. Unfortunately, we demonstrate that their scheme cannot withstand public
key replacement attacks and is not secure against coalition attacks from malicious sensor …