An Efficient Signcryption Scheme from q-Diffie-Hellman Problems

Confidentiality and authenticity are two fundamental security requirement of Public key Cryptography. These are achieved by encryption scheme and digital signatures respectively. Here we present a provably secure signcryption scheme in random oracle model by modifying Libert et al’s scheme [2]. Our scheme is more efficient and secure than Libert et al’s scheme. Tan [1] proved that this scheme is not secure against nonadaptive chosen cipher text attacks. It has been also proved that the semantically secure symmetric encryption scheme proposed in the Libert et al’s scheme is not sufficient to guarantee to be secure against adaptive chosen ciphertext attacks. Here we proposed a modified version of Libert et al’s scheme. The security of which is proven using two assumptions, namely the Strong Diffie-Hellman (SDH) and Diffie-Hellman Inversion (DHI) in the random oracle model.