An Identity-Based Threshold Signcryption Scheme with Semantic Security

Through cryptanalysis of the improved scheme of a generalized group-oriented threshold signcryption schemes, it is found that the improved scheme can effectively resist conspiracy attack and forgery attack, but does not have semantic security and public verification function, and sends threshold signcryption by the secret secure channel, which increases the communication costs and potential safety hazards of the system. A new group-oriented publicly verifiable threshold signcryption scheme is proposed on the basis of the improved scheme, the new scheme overcomes the drawbacks of the improved scheme, which not only provides with semantic security and public verification function, but also can send threshold signcryption by the public channel.

In recent years, secure communication and privacy‐preserving are gaining popularity because of the advent of wireless network. Certificateless cryptography (CLC) and identity‐based cryptography (IBC) have already been widely applied in the area of wireless network. Hence, to achieve secure communication from CLC to IBC, we present a heterogeneous signcryption scheme that enables a sender in the CLC to transmit a message to multi‐receiver in the IBC. Our scheme has no restrictions on the system parameters and master keys; private key generator and key generating center generate their own system parameters and master key for the IBC users and the CLC user, separately. Considering privacy‐preserving in heterogeneous communication, we show that our scheme can realize the anonymity of all receivers. Compared with other schemes, our scheme has more advantages, such as public verification and decryption fairness, which are attractive for wireless network applications. Moreover, our scheme has the indistinguishability against adaptive chosen ciphertext attacks, the existential unforgeability against adaptive chosen messages attacks, and anonymous indistinguishability of encryptions under selective‐ID, chosen ciphertext attack in the random oracle model. Copyright © 2016 John Wiley & Sons, Ltd.

Certificateless cryptography introduced by Al-Riyami and Paterson eliminates the key escrow problem inherent in identity based cryptosystems. Even though building practical identity based signcryption schemes without bilinear pairing are considered to be almost impossible, it will be interesting to explore possibilities of constructing such systems in other settings like certificateless cryptography. Often for practical systems, bilinear pairings are considered to induce computational overhead. Signcryption is a powerful primitive that offers both confidentiality and authenticity to noteworthy messages. Though some prior attempts were made for designing certificateless signcryption schemes, almost all the known ones have security weaknesses. Specifically, in this paper we demonstrate the security weakness of the schemes in [2], [1] and [6]. We also present the first provably secure certificateless signcryption scheme without bilinear pairing and prove it in the random oracle model.

Proxy signcryption is a cryptographic primitive which combines the functionalities of a proxy signature scheme and a signcryption scheme. In this paper, based on bilinear pairings, we would like to propose two efficient proxy singcryption schemes. One is certificate based and the other is identity based. Also we analyze the two proposed schemes from efficiency point of view. We show that the certificate based scheme achieves great efficiency in terms of communication cost and computation overhead. And the identity based scheme is much more efficient than the scheme proposed by Li and Chen. What’s more, we also argument that the two proposed schemes are secure in the random oracle model without a secure channel.Keywordsproxy signaturesigncryptionproxy signcryptionbilinear pairings

In this paper, we introduce a new type of identity based signature (IBS) scheme that we call fuzzy identity based signature (FIBS). In a FIBS scheme, user's identity are viewed as set of descriptive attributes. A user can use attributes omega to verify a signature signed with the attributes omega' if and only if omega and omega' are within a certain distance of each other as judged by some metric. We present a FIBS scheme from bilinear pairings. The proposed FIBS scheme is both error-tolerant and secure against collusion attacks. We also prove that the proposed FIBS scheme is existentially unforgeable under a chosen message attack and selective fuzzy identity attack in the random oracle model, given that the (k + 1)-EP problem (where k = 2) is hard.

In this paper, we first construct a security model for delegation-by-warrant ID-based proxy signcryption schemes and formalize notions of security for them. To the best of our knowledge, no related work has been done. Then we present such a scheme based on the bilinear pairings, and show that it is provably secure in the random oracle model. Specifically, we prove its semantic security under the DBDH assumption and its unforgeability under the BDH assumption.

A server-aided verification signature scheme consists of a digital signature scheme and a server-aided verification protocol. By executing the server-aided verification protocol with the server, one can perform the verification of signatures with less computational cost compared to the original verification algorithm. This mechanism is therefore indispensable for low-power devices such as smart cards. The contributions of this paper are manyfold. Firstly, we introduce and define the existential unforgeability of server-aided verification signatures. We prove that the new notion includes the existing security requirements in server-aided verification signatures. Then, we analyze the Girault-Lefranc scheme in Asiacrypt 2005 and show that their scheme can be made secure in our model, but the computational cost is more than the claimed in the original scheme. After that, we propose the first server-aided verification BLS, which is existentially unforgeable in the random oracle model under the Bilinear Diffie-Hellman assumption. Finally, we consider the collusion and adaptive chosen message attack in server-aided verification signatures. For the first time in the literature, the security of server-aided verification signatures against such attacks is defined. We provide a concrete construction of a server-aided verification BLS secure against the collusion and chosen message attack.

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.

As a variation of ordinary digital signature scheme, a proxy signature scheme enables a proxy signer to sign messages on behalf of the original signer. Proxy multi-signature is an extension of the basic proxy signature primitive, and permits two or more entities to delegate their signing capabilities to some other entity. Many identity-based proxy multi signature (IBPMS) schemes using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately more than ten times of the scalar multiplication over elliptic curve group. In order to save the running time and the size of the signature, in this paper, we propose an IBPMS scheme without bilinear pairings. We also prove the security of our scheme against adaptive chosen message attack under random oracle model. With the running time being saved greatly, our scheme is more applicable than the previous related schemes for practical applications.KeywordsDigital signatureIdentity-based cryptographyProxy-multi signatureElliptic curve discrete log problem

Signcryption is a useful cryptographic primitive which simultaneously performs encryption and signature with cost less than the signature-then-encryption approach. Identity-based signcryption (IBSC) eliminates the complicated management of certificates in signcryption schemes in the traditional public-key infrastructure (PKI) setting. Most IBSC schemes are constructed in the random oracle model, while it is unknown how to instantiate a really ``random oracle in the real world. By exploiting Boneh et al.'s strongly unforgeable signature and Paterson et al.'s identity-based signature, this paper proposes a new IBSC scheme in the standard model. It is proven that our IBSC scheme satisfies semantic security and strong unforgeability under the bilinear decision Diffie-Hellman (BDDH) assumption. The proofs do not rely on random oracles. Performance analysis shows that our scheme is also efficient and practical.

Proxy signcryption is a novel cryptographic primitive that combines the functionality of a proxy signature with that of a signcryption. However, the security of all the known proxy signcryption schemes were proven in the random oracle, which has received a lot of criticism that the proofs in the random oracle model are not sound with respect to the standard model. Hence, it is an interesting research problem on how to construct a provably secure proxy signcryption scheme in the standard model. In this paper, motivated by Waters' signature scheme, we propose a new construction of proxy signcryption scheme based on bilinear pairing without using random oracles. Then, we use the techniques from provable security to show that the proposed scheme is indistinguishability under adaptive chosen ciphertext attacks secure under the decisional bilinear Diffie–Hellman assumption and existentially unforgeable under the computational Diffie–Hellman assumptions. Compared with the existing schemes with formal security proof, we show that no pairing computation is required in our proxy signcrypt phase with pre‐computations. To the best of our knowledge, our proposed scheme is the first provably secure proxy signcryption scheme in the standard model. Copyright © 2014 John Wiley & Sons, Ltd.

Certificateless aggregate signcryption: Security model and a concrete construction secure in the random oracle model

An important advantage of signcryption schemes compared to one pass key exchange protocols is non-interactive non-repudiation (NINR). This attribute offers to the receiver of a signcrypted ciphertext the ability to generate a non-repudiation evidence, that can be verified by a third party without executing a costly multi-round protocol. We propose a computational Diffie–Hellman based insider secure signcryption scheme with non-interactive non-repudiation. Namely, we show that under the computational Diffie–Hellman assumption and the random oracle model, our scheme is tightly insider secure, provided the underlying encryption scheme is semantically secure. Compared to a large majority of the previously proposed signcryption schemes with NINR, our construction is more efficient and it does not use any specificity of the underlying group, such as pairings. The communication overhead of our construction, compared to Chevallier Mâmes’ signature scheme is one group element.

The concept of policy-based cryptography is a promising paradigm for trust establishment and authorization in largescale open environments like the Internet and Mobile Networks. It aims at providing a framework for performing cryptographic operations with respect to policies formalized as monotone Boolean expressions written in standard normal forms. A policy involves conjunctions and disjunctions of conditions where each condition is fulfilled by a digital credential representing the signature of a specific credential issuer on a set of statements about a certain entity. Therefore, an entity fulfills a policy if any only if it has been issued a set of credentials fulfilling the combination of conditions specified by the policy.In this work, we focus on policy-based encryption schemes which allow to encrypt a message according to a policy so that only entities fulfilling the policy are able to decrypt the message. More generally, policy-based encryption belongs to an emerging family of encryption schemes sharing the ability to integrate encryption with access control structures. This ability is mainly enabled by bilinear pairings over elliptic curves and allows for several interesting applications in different contexts.A policy-based encryption scheme has to fulfill two primary requirements: on one hand, provable security under well defined attack models. On the other hand, efficiency, especially when dealing with the conjunctions and disjunctions of credential-based conditions.The contributions of our research work are twofold:1. The standard acceptable notion of security for public-key encryption schemes is indistinguishability against chosen ciphertext attacks. Hence, it is natural to require that a policy-based encryption scheme also satisfies this strong notion of security. However, the definition of this security notion must be adapted to the policy-based setting. Our first contribution is the definition of policy-oriented security model for policy-based encryption schemes as well as the development of an efficient policy-based encryption scheme that is provably secure under our security model in the random oracle model.2. Policy-based encryption schemes may suffer from the key-escrow property i.e. in addition to the legitimate holder of the credentials fulfilling the encryption policy, any collusion of credential issuers who are able to issue a set of credentials fulfilling the policy can decrypt the message. Our second contribution is to address this issue through the notion of policy-based public-key encryption. The latter allows encrypting a message not only with respect to a policy but also according to a public-key so that only an entity fulfilling the policy and having access to the corresponding private-key is able to decrypt the message. We developed a policy-based public-key encryption scheme from bilinear pairings and proved its security under the corresponding security model. Our proposal improves related work in terms of both security and efficiency.

In recent years, many password authenticated key exchange (PAKE) protocols have been proposed. However, many of them have been broken or have no security proof. In this paper, we propose an efficient password authenticated key exchange protocol using bilinear pairings. Compared with previous PAKE protocol using bilinear pairings, our protocol is quite efficient both in communication cost and computational cost. Moreover, this paper proves that the novel protocol is forward secrecy under the Bilinear Diffie-Hellman (BDH) assumption in the random oracle model.KeywordsPAKEbilinear paringBDHforward secrecy