Biblio

Smart substation and Vehicular Ad-Hoc Network (VANET) are two important applications of aggregate signature scheme. Due to the large number of data collection equipment in substation, it needs security authentication and integrity protection to transmit data. Similarly, in VANET, due to limited resources, it has the needs of privacy protection and improving computing efficiency. Aggregate signature scheme can satisfy the above these needs and realize one-time verification of signature for multi-terminal data collection which can improve the performance. Aggregate signature scheme is an important technology to solve network security problem. Recently, many aggregate signature schemes are proposed which can be applied in smart grid or VANET. In this paper, we present two security analyses on two aggregate signature schemes proposed recently. By analysis, it shows that the two aggregate signature schemes do not satisfy the security property of unforgeability. A malicious user can forge a signature on any message. We also present some improved methods to solve these security problems with better performance. From security analysis to improvement of aggregate signature scheme, it is very suitable to be an instance to exhibit the students on designing of security aggregate signature scheme for network security education or course.

Forward secure proxy signature (FoSPS) solves the security drawback of private key exposure problem of generating the private key of each time interval. Directed signature scheme solves the public signature verification problem in traditional digital signature by designating the constant one as the signature verifier. Due to excellent properties, the two signature schemes have attracted the research of many experts. Recently, based on the Elliptic curve cryptography (ECC), a new FoSPS scheme and directed signature scheme were proposed. In this paper, we analyze the two schemes and present which the either of both schemes is insecure and do not satisfy the unforgeability. In other words, anyone is able to forge a valid signature but the one does not know the signer's secret key. In the same time, we give the main reasons why the enemy is able to forge the signature by analyzing the two schemes respectively. And we also present a simple improvement idea to overcome existing problems without adding extra computational cost which can make them applied in some environments such as e-medical information system.