Cryptanalysis of a Certificateless Aggregate Signature Scheme for Healthcare Wireless Sensor Network

Certificateless aggregate signatures aggregate n signatures from n different users into one signature. Therefore, a verifier can judge whether all signatures are valid by verifying once. With this advantage, certificateless aggregate signatures are widely used in the environment of limited computing resources. Recently, a novel certificateless aggregate signature scheme was proposed by Kumar et al. This scheme's security was claimed to be secure against two types of attackers under the random oracle model. In this paper, we indicate that their scheme is unable to achieve this security goal. We show an attack algorithm that the second type of attacker could forge a valid signature under an identity without the private key of the target user. Moreover, we demonstrate that the second type of attacker could forge a valid aggregate signature.