Security Analysis and Improvement of Designated Verifier CLAS in Network Security Course Education

Cryptographic algorithm plays an important role in the teaching of network security course. Certificateless aggregate signature (CLAS) scheme is an important cryptographic algorithm in cryptography. Many CLAS schemes have been proposed with some property, such as designated verifier property. Designated verifier property makes it possible for a specific person to verify the signature which can be applied in many scenes, such as medicine and biology system and et al. In this paper, we analyze a CLAS scheme with designated verifier property proposed in 2020 which satisfies designated verifiability property, unforgeability property and non-transitivity property. However, we point out that the CLAS scheme does not satisfy the unforgeability as they claimed. We present two improved methods to overcome these existed security drawbacks. By analyzing the security of a CLAS scheme and proposing some improved methods, it can let students know how to better design a secure cryptographic algorithm in process of network security course.