Cryptanalysis and Modification of an Improved Self-Certified Digital Signature Scheme with Message Recovery

Digital signature plays a key role in bringing authenticity to cryptographic communications. A signature scheme with message recovery has two characteristics. The public key of the signer can be authenticated while verifying the signature, and the receiver is able to obtain the message. In 2013, Wu and Xu presented a self-certified digital signature scheme with message recovery by combining the two concepts of digital signature with message recovery and self-certified public key. They also claimed that their scheme provides provable security against man-in-the-middle attack, forgery attack, and message leakage. This paper first reviews the scheme of Wu and Xu, and then presents an insider forgery attack to this scheme. It will be shown that this scheme is not secure against insider forgery attack. A modification is proposed in order to overcome this weakness