Sign Secret Technology. Public Key Cryptography

1997 Zheng proposed a novel cryptographic primitive which called signcryption. Signcryption can achieve both the signature and encrytion function in a logic step and is with the cost lower than common way "first signature and then encrytion'', thus is an ideal way to achieve information storage and transmitted secretly and verifiably. Signcryption schemes are compact and particularly suited for efficiency-critical applications such as secure ATM networks, secure and authenticated key establishment, secure multi-casting over the Internet, authenticated key recovery.The main research results in this paper in(?)des:1. The scheme proposed by Zheng can provide both encryption and signature characteristics in a economical way. The original scheme may satisfy confidentiality, verifiability, but can not provide non-repudiation, forward security and public ver-ifiability. Then we propose a new modified scheme on the basis of Zheng's original scheme, which can offer the public verifiability.2. This paper proposes an Identity-Based Signcryption scheme which without a trusted party.3. The author analyzes Li-Chen scheme and gives security attacks to prove that the schenme does not satisfy strong unforgeability and forward security. At the same time, we propose a new scheme which can satisfy strong unforgeability. Furthermore, there is no secure channel needed in our schemes so they are more efficient than Li-Chen scheme.