On Security Notions for Verifiable Encrypted Signature
First we revisit three - BGLS, MBGLS and GZZ verifiably encrypted signature schemes[2,3,6].We find that they are all not strong unforgeable.We remark that the notion of existential unforgeable is not sufficient for fair exchange protocols in most circumstances.So we propose three new - NBGLS, MBGLS and NGZZ verifiably encrypted signature schemes which are strong unforgeable. Also we reconsider other two - ZSS and CA verifiably encrypted signature schemes[4,8], we find that they both cannot resist replacing public key attack. So we strongly suggest that strong unforgeable for verifiably encrypted signature maybe a better notion than existential unforgeable and checking adjudicator knowing its private key is a necessary step for secure verifiably encrypted signature scheme.
Provable Secure Generalized Signcryption
Generalized Signcryption is a new cryptographic primitive which can work as an encryption scheme, a signature scheme or a signcryption scheme. We give security notions of Generalized Signcryption and improve a Generalized Signcryption scheme proposed by Han et al.We give the formal attacking model of this new cryptographic primitive in the framework of theory of provable security. At last, we give formal proofs for this new improved Generalized Signcryption in our attacking model.