A New Efficient Publicly Verifiable Signcryption Scheme and Its Multiple Recipients Variant

Signcryption is a novel public key primitive first proposed by Zheng in 1997 to achieve the functionality of both an encryption scheme and a signature scheme simultaneously. It therefore offers the three services: privacy, authenticity and non-repudiation. Although Zheng´s signcryption scheme was formally proven to be secure, it is not easy to fulfill the property of nonrepudiation since the signature cannot be verified publicly. To overcome this problem many signcryption schemes, as Bao-Deng scheme, were designed so that the signature is publicly verifiable but this was at the cost of reducing the efficiency compared with the original signcryption scheme. In this paper we propose a signcryption scheme that achieves the public verifiability property with keeping the same efficiency as the original scheme. Also we introduce a multiple recipients variant of the proposed scheme that is more efficient than Zheng´s multiple recipients signcryption scheme. The security of our scheme is based on the intractability of the discrete logarithm problem (DLP) and the Diffie-Hellman problem (DHP).