On the Security of a Certificateless Strong Designated Verifier Signature Scheme

Recently, Chen et al. proposed the first non-delegatable certificateless strong designated verifier signature scheme and claimed that their scheme achieves all security requirements. However, in this paper, we disprove their claim and present a concrete attack which shows that their proposed scheme is forgeable. More precisely, we show that there exist adversaries who are able to forge any signer\u27s signature for any designated verifier on any message of his choice

A new certificateless signature with enhanced security and aggregation version

To satisfy the applications in certificateless environment, many researchers have been investigating certificateless aggregate signature schemes. Several schemes that are independent with the aggregated numbers are proposed to reduce the computation overhead. In these schemes, the pairing computations that in verification procedure needs are a constant value. Recently, Hou et al. proposed an improved certificateless aggregate signature scheme. They demonstrated the scheme is provably secure in the random oracle model. However, we find that their scheme is insecure in their security model by giving a concrete attack. Then, we propose an improved certificateless signature scheme and use it to construct a new certificateless signature scheme with enhanced security and aggregation. Furthermore, we provide formal security proof of our new scheme. Compared with other four schemes, our enhanced protocol is more suitable for realistic applications