A Provably Secure Certificateless User Authentication Protocol for Mobile Client-Server Environment

Deniable authentication allows a receiver to identify the source of a given message, but cannot prove the source of a given message to any third party. It can be employed in electronic voting (e-voting) systems, electronic tendering (e-tendering) systems and secure networks negotiation. These applications can be well realised in ad hoc networks. Therefore, deniable authentication is an essential security requirement for ad hoc networks. Aggregate deniable authentication is a method for combining n authenticator of n distinct messages from n distinct users into one single authenticator. This feature is very attractive in bandwidth-limited ad hoc networks. In this paper, we present an efficient certificateless aggregate deniable authentication protocol. Our protocol is based on certificateless public key cryptography that has neither the public key certificates management problem in traditional public key infrastructure (PKI) cryptography nor the key escrow problem in identity-based cryptography. The security of our protocol can be proven in the random oracle model under the bilinear Diffie-Hellman (BDH) and computational Diffie-Hellman (CDH) problems. In addition, our protocol adopts aggregate verification that can speed up the verification of authenticators. Our protocol is very suitable for ad hoc networks.

Certificateless public key cryptography is a new paradigm introduced by AI-Riyami and Paterson. It eliminates the need of the certificates in traditional public key cryptosystems and the key escrow problem in Identity-based Public Key Cryptography (ID-PKC). Due to the advantages of the certificateless public key cryptography, we propose a novel certificateless blind signature scheme based on pairings in the paper. Firstly, we give formal security definitions of blindness and unforgeability in our scheme. Then an concrete instance is given and we show that the proposed scheme is provably secure in the random oracle model. The security of our schemes is proven based on the hardness of computational Diffie-Hellman problem and the bilinear pairing inversion Problem (BPI). Finally, by comparing our scheme with Zhang's scheme in terms of computational cost and the signature size, we show that our scheme is more efficient, since no pairing computation is required in the signing, and only one pairing computation is required in the verifying phase.

Certificateless threshold signature scheme from bilinear maps

Certificateless public key cryptography (CL-PKC) can solve the problems of certificate management in a public key infrastructure (PKI) and of key escrows in identity-based public key cryptography (ID-PKC). In CL-PKC, the key generation center (KGC) does not know the private keys of all users, and their public keys need not be certificated by certification authority (CA). At present, however, most certificateless encryption schemes are based on large integer factorization and discrete logarithms that are not secure in a quantum environment and the computation complexity is high. To solve these problems, we propose a new certificate-less encryption scheme based on lattices, more precisely, using the hardness of the learning with errors (LWE) problem. Compared with schemes based on large integer factorization and discrete logarithms, the most operations are matrixvector multiplication and inner products in our scheme, our approach has lower computation complexity. Our scheme can be proven to be indistinguishability chosen ciphertext attacks (IND-CPA) secure in the random oracle model.

Identity-based Cryptography (IBC) is an exciting alternative to public-key Cryptography (PKC), as it eliminates the need for certificate that is a major issue in PKC. However, IBC suffers from an additional limitation viz. the key escrow problem — that is — a user's private key is generated by the central trusted Key Generation Centre (KGC) — that being a single entity, lends itself to the security vulnerabilities in the cryptosystem. One of the prominent solutions proposed as Secure Key Issuing Protocol by Lee. et al. which uses a distributed protocol to generate the private key for user. However, this approach entails significant communications overhead. Hence, in this paper we have proposed an improved Identity based Secure Key Generation Protocol that gives the complete solution of key escrow problem, using clustering based approach. The proposed scheme involves less number of authorities in the computation of the public/private key pair and hence is more efficient. As we further analyze in the paper, our protocol also provides protection against the possible collusion attack in Lee's protocol. To the best of our knowledge, this is a simple, yet efficient and unique attempt to overcome the key escrow problem in IBCs.

Ring signature is a kind of digital signature which can protect the identity of the signer. Certificateless public key cryptography not only overcomes key escrow problem but also does not lose some advantages of identity‐based cryptography. Certificateless ring signature integrates ring signature with certificateless public key cryptography. In this paper, we propose an efficient certificateless ring signature; it has only three bilinear pairing operations in the verify algorithm. The scheme is proved to be unforgeable in the random oracle model.

Certificateless public key cryptography(CL-PKC)is a new paradigm in public key cryptography.It effectively solves the inherent key escrow problem in identity based public key cryptography(ID-PKC)while keeps its certificate free property.Designing efficient and secure signature schemes in certificateless public key setting is an interesting research topic that attracts the attentions of many researchers.This paper proposes a new method to construct a class of certificateless signature schemes.The schemes constructed using the new method can be proven secure in a very strong security model.The overall performances of the authors' newly constructed schemes are better than that of the other certificateless signature schemes available in the literature.

Since certificateless public key cryptosystem can solve the complex certificate management problem in the traditional public key cryptosystem and the key escrow problem in identity-based cryptosystem and the pairing computation is slower than scalar multiplication over the elliptic curve, how to design certificateless signature (CLS) scheme without bilinear pairings is a challenge. In this paper, we first propose a new pairing-free CLS scheme, and then the security proof is presented in the random oracle model (ROM) under the discrete logarithm assumption. The proposed scheme is more efficient than the previous CLS schemes in terms of computation and communication costs and is more suitable for the applications of low-bandwidth environments.

Certificate-based cryptography is a new cryptographic primitive which eliminates the necessity of certificates in the traditional public key cryptography and simultaneously overcomes the inherent key escrow problem suffered in identity-based cryptography. However, to the best of our knowledge, all existed constructions of certificate-based encryption so far have to be based on the bilinear pairings. The pairing calculation is perceived to be expensive compared with normal operations such as modular exponentiations in finite fields. The costly pairing computation prevents it from wide application, especially for the computation limited wireless sensor networks. In order to improve efficiency, we propose a new certificate-based encryption scheme that does not depend on the pairing computation. Based on the decision Diffie-Hellman problem assumption, the schemes security is proved to be against the chosen ciphertext attack in the random oracle. Performance comparisons show that our scheme outperforms the existing schemes.

PCAS: Cryptanalysis and improvement of pairing-free certificateless aggregate signature scheme with conditional privacy-preserving for VANETs

Certificateless public key cryptography (CL-PKC) is an important type of public key cryptography, which effectively solves the inherent key escrow problem in identity based public key cryptography while keeps its certificate-free property. As the adversarial models in CL-PKC are relatively complex, designing efficient and secure certificate less encryption schemes in the standard model has been an interesting and challenging research topic. In this paper, we give cryptanalysis to an existing certificate less encryption scheme in the standard model. We show its insecurity by demonstrating two kinds of attacks.

Featuring no key escrow and no certificate, certificateless public key cryptography (CLPKC) has received much attention. A necessary problem in CLPKC is how to revoke a compromised/misbehaving user, which still remains to be efficiently solved: all existing methods are not practical for use owing to either enormous computation (secret channels), or a costly mediator. In this paper, we present a new approach for revocation in CLPKC and give a revocable certificateless encryption (RCLE) scheme. In the new scheme, a user's private key contains three parts: an initial partial private key, a time key and a secret value. The time key is updated at every time period and is transmitted over a public channel. Our construction offers higher performance than previous solutions. Based on the bilinear Diffie-Hellman problem, our RCLE scheme is provably secure in the random oracle model.

Signcryption is a cryptographic technique that provides both confidentiality and authenticity of data during public transmission in many modern applications like Internet -of -Things (IoT), Wireless Sensor Networks (WSNs) etc. The functionalities of encryption and Signature can achieve simultaneously through the signcryption with lower computational cost and communication overheads than those of traditional sign-then-encrypt approach. Many signcryption schemes have been constructed by various researchers in different cryptographic frameworks. Certificateless cryptography is one of the recent public key cryptography which eliminates the key escrow problem and complex certificate management problemsin identity based cryptography and traditional public key cryptography respectively. Providing the security and efficiency in many modern applications including IoT and WSNs is a crucial task. In this paper, we proposed new signcryption scheme in certificateless cryptography. This scheme supports the property of public verifiability and is secure against various types of adversaries in the random oracle model with the assumption that the Computational Diffie-Hellman Problem (CDHP) and the Elliptic Curve Discrete Logarithmic Problems (ECDLP) are hard. Due to pairing-free environment the proposed scheme is computationally more efficient than the existing public verifiable signcryption schemes.

Cloud storage service supplies people with an efficient method to share data within a group. The cloud server is not trustworthy, so lots of remote data possession checking (RDPC) protocols are proposed and thought to be an effective way to ensure the data integrity. However, most of RDPC protocols are based on the mechanism of traditional public key infrastructure (PKI), which has obvious security flaw and bears big burden of certificate management. To avoid this shortcoming, identity-based cryptography (IBC) is often chosen to be the basis of RDPC. Unfortunately, IBC has an inherent drawback of key escrow. To solve these problems, we utilize the technique of certificateless signature to present a new RDPC protocol for checking the integrity of data shared among a group. In our scheme, user's private key includes two parts: a partial key generated by the group manager and a secret value chosen by herself/himself. To ensure the right public keys are chosen during the data integrity checking, the public key of each user is associated with her unique identity, for example the name or telephone number. Thus, the certificate is not needed and the problem of key escrow is eliminated too. Meanwhile, the data integrity can still be audited by public verifier without downloading the whole data. In addition, our scheme also supports efficient user revocation from the group. The security of our scheme is reduced to the assumptions of computational Diffie-Hellman (CDH) and discrete logarithm (DL). Experiment results exhibit that the new protocol is very efficient and feasible.

A secure and efficient AKE scheme for IoT devices using PUF and cancellable biometrics