A novel designated receiver based convertible multi-signcryption scheme

This paper presents a convertible multi-signcryption scheme based on the security of three computationally hard problems, namely computationally Diffie-Helmann problem (CDH), Discrete Logarithmic Problem (DLP) and Integer Factorization problem. The uniqueness of this scheme is, a message is signcrypted by more than two signcrypters and only a designated receiver can verify the signcrypted text. The proposed scheme is convertible as it can easily produce the ordinary signature without the co-operation from any one of the signcrypters. The scheme has been proved to be secure against active attacks, such as, chosen ciphertext attack and forgery attack. In case of a later dispute on repudiation, the recipient has the ability to convert the authenticated signcrypted text into an ordinary one for convincing anyone of the signer´s dishonesty. This scheme is more efficient for multi-party applications since the size of the generated signcrypted text is independent of the number of total participating signcrypters. In addition, the computational costs for the verifier will not increase even after increasing the number of signcrypters. This scheme is secure enough to be applicable in practical areas where information security is desirable, such as, press releases, e-commerce applications and digital rights management.