Blockchain as a CA: A Provably Secure Signcryption Scheme Leveraging Blockchains

Although encryption and signatures have been two fundamental technologies for cryptosystems, they still receive considerable attention in academia due to the focus on reducing computational costs and communication overhead. In the past decade, applying certificateless signcryption schemes to solve the higher cost of maintaining the certificate chain issued by a certificate authority (CA) has been studied. With the recent increase in the interest in blockchains, signcryption is being revisited as a new possibility. The concepts of a blockchain as a CA and a transaction as a certificate proposed in this paper aim to use a blockchain without CAs or a trusted third party (TTP). The proposed provably secure signcryption scheme implements a designated recipient beforehand such that a sender can cryptographically facilitate the interoperation on the blockchain information with the designated recipient. Thus, the proposed scheme benefits from the following advantages: (1) it removes the high maintenance cost from involving CAs or a TTP, (2) it seamlessly integrates with blockchains, and (3) it provides confidential transactions. This paper also presents the theoretical security analysis and assesses the performance via the simulation results. Upon evaluating the operational cost in real currency based on Ethereum, the experimental results demonstrate that the proposed scheme only requires a small cost as a fee.