Certificateless cryptography involves a Key Generation Center (KGC) which issues a partial key to a user and the user also independently generates an additional public/secret key pair in such a way that the KGC who knows only the partial key but not the additional secret key is not able to do any cryptographic operation on behalf of the user; and a third party who replaces the public/secret key pair but does not know the partial key cannot do any cryptographic operation as the user either. We call this attack launched by the third party as the key replacement attack. In ACISP 2004, Yum and Lee proposed a generic construction of digital signature schemes under the framework of certificateless cryptography. In this paper, we show that their generic construction is insecure against key replacement attack. In particular, we show that the security requirements of their generic building blocks are insufficient to support some security claim stated in their paper. We then propose a modification of their scheme and show its security in a new and simplified security model. We show that our simplified definition and adversarial model not only capture all the distinct features of certificateless signature but are also more versatile when compared with all the comparable ones. We believe that the model itself is of independent interest.

Key replacement attack against a generic construction of certificateless signature

The concept of aggregate signcryption was first introduced in 2009 by Selvi et al. Identity based aggregate signcryption schemes, Lecture Notes in Computer Science 5922 LNCS, 2009, pp. 378-397. The aggregation process of these schemes reduces the amount of exchanged information and is particularly useful in low-bandwidth communication networks and computationally-restricted environments such as wireless sensor networks. Selvi et al.'s scheme is in the identity-based setting and suffers from the key escrow problem. The goal of this paper is to overcome this problem and propose a suitable security model for aggregate signcryption in the certificateless setting. We further propose a concrete certificateless aggregate signcryption scheme which is based on Barbosa and Farshim's certificateless signcryption scheme Certificateless signcryption. In: M. Abe, V. Gligor (Eds.), Proceedings of the 2008 ACM Symposium on Information, Computer and Communications Security (ASIACCS-08), ACM, New York. pp. 369-372. We then prove the security of the proposed scheme in the random oracle model under the gap Bilinear Diffie-Hellman and computational Diffie-Hellman intractability assumptions.

Certificateless aggregate signcryption

The communication model of Internet of Things IOT application has some shortcomings in user privacy protection and information security. To solve these shortcomings, we define the formal models of certificateless online/offline signcryption and propose a concrete certificateless online/offline signcryption scheme for IOT environment. Compared with the existing identity-based online/offline signcryption schemes that do not require the plaintext and the receiver's identity in the offline phase, our scheme has the great advantage of the offline computation cost, offline storage, ciphertext length, and receiver computation cost. Moreover, our scheme achieves known session-specific temporary information security, public verifiability with confidentiality and no key escrow problem. Copyright © 2013 John Wiley & Sons, Ltd.

A security communication model based on certificateless online/offline signcryption for Internet of Things

Certificateless strong designated verifier signature schemes have realized the merit of CL-PKC against the traditional strong designated verifier signatures. However, when the signer and the designated verifier disagree with the signature, existing schemes cannot distinguish the original signature from the signature transcript. In addition, errors or malicious actions introduced by the designated verifier may lead to the failure of signature verification. To solve these issues, we propose a certificateless verifiable strong designated verifier signature scheme. When disputes arise between the signer and the verifier, the scheme can effectively prevent the signer from denying the signature generated by the signer, as well as the designated verifier from denying valid signatures or invalid ones. Our scheme does not rely on bilinear pairings. The proposed scheme satisfies the requirements of verifiability, unforgeability, non-delegability, non-transferability and signer ambiguity. We also provide formal security proof in the random oracle model for the proposed scheme.

/pdf/a-certificateless-verifiable-strong-designated-verifier-18ovenpv54.pdf

A Certificateless Verifiable Strong Designated Verifier Signature Scheme

Certificateless cryptography addresses the private key escrow problem in identity-based systems, while overcoming the costly issues in traditional public key cryptography. Undeniable signature schemes were proposed with the aim of limiting the public verifiability of ordinary digital signatures. The first certificateless undeniable signature scheme was put forth by Duan. The proposed scheme can be considered as the certificateless version of the identity-based undeniable signature scheme which was introduced by Libert and Quisquater. In this paper, we propose a new scheme which is much more efficient comparing to Duan's scheme. Our scheme requires only one pairing evaluation for signature generation and provides more efficient confirmation and disavowal protocols for both the signer and the verifier. We also prove the security of our scheme in the strong security model based on the intractability of some well-known pairing-based assumptions in the random oracle model.

Wei Zhao

Papers

Certificateless undeniable signatures from bilinear maps