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As many electronic items are exchanged over the Internet recently, the fair exchange problem becomes of a greater importance. When constructing fair exchange systems, verifiably encrypted signatures are usually used as a building block. Hence, we propose an efficient ID-based verifiably encrypted signature scheme based on Hess's signature scheme because it is known as a concise and secure signature scheme in ID-PKC. Our scheme does not need registrations between users and a trusted third party called an adjudicator, does not need zero-knowledge proof, and uses an optimized adjudicator who participates in the protocol only when problem occurs. Together with a formal model, we analyze security and efficiency of our scheme and show that it is more suitable for communication requirements than previous schemes of same kind. [ABSTRACT FROM AUTHOR]

Despite many advantages of identity (ID)-based cryptosystems in removing certificates of public keys over the traditional public key cryptosystems (PKC), some problems related to the inherent key escrow property, user authentication and the need for the confidential channel for private key distribution remain as important issues to be resolved. In this paper, we propose a new key issuing scheme reasonably reducing the burden employed to a trust key issuing authority called key generation center (KGC) in checking the identifications of all users maintained by the KGC by means of separating the duties of the KGC; user identification function by a local trust authority, and private key extracting and issuing function by the KGC, respectively. Furthermore, our scheme provides secure transmission channel through blinding technique between the KGC and users, and deals efficiently with the key escrow problem. Hence, our scheme makes ID-PKC more applicable to real environment, and cover the wider area. [ABSTRACT FROM AUTHOR]

In this paper, we analyze some serious weakness for security of existing key issuing schemes in identity(ID)-based cryptosystems which were proposed in order to eliminate key escrow property and remove the need of secure channel, and describe some attacks for them. In addition, we present the improved key issuing protocols for each scheme with weakness, which can resist the attack and overcome key escrow problem. [ABSTRACT FROM AUTHOR]