Signcryption schemes with threshold unsigncryption, and applications

The final publication is available at link.springer.comThe goal of a signcryption scheme is to achieve the same functionalities as encryption and signature together, but in a more efficient way than encrypting and signing separately. To increase security and reliability in some applications, the unsigncryption phase can be distributed among a group of users, through a (t, n)-threshold process. In this work we consider this task of threshold unsigncryption, which has received very few attention from the cryptographic literature up to now (maybe surprisingly, due to its potential applications). First we describe in detail the security requirements that a scheme for such a task should satisfy: existential unforgeability and indistinguishability, under insider chosen message/ciphertext attacks, in a multi-user setting. Then we show that generic constructions of signcryption schemes (by combining encryption and signature schemes) do not offer this level of security in the scenario of threshold unsigncryption. For this reason, we propose two new protocols for threshold unsigncryption, which we prove to be secure, one in the random oracle model and one in the standard model. The two proposed schemes enjoy an additional property that can be very useful. Namely, the unsigncryption protocol can be divided in two phases: a first one where the authenticity of the ciphertext is verified, maybe by a single party; and a second one where the ciphertext is decrypted by a subset of t receivers, without using the identity of the sender. As a consequence, the schemes can be used in applications requiring some level of anonymity, such as electronic auctions.Peer ReviewedPostprint (author's final draft

SIGNCRYPTION ANALYZE

The aim of this paper is to provide an overview for the research that has been done so far in signcryption area. The paper also presents the extensions for the signcryption scheme and discusses the security in signcryption. The main contribution to this paper represents the implementation of the signcryption algorithm with the examples provided.ElGamal, elliptic curves, encryption, identity-based, proxy-signcryption, public key, ring-signcryption, RSA, signcryption

nMIBAS: A Novel Multi-Receiver ID-Based Anonymous Signcryption with Decryption Fairness

Based on the ring signature technology, the multi-receiver ID-based anonymous signcryption (MIBAS) is proposed, and its goal is to protect the privacy of the sender or so-called signer. In an MIBAS scheme, every receiver can verify whether the sender is a member of a trusted group and thus ensure the reliability of the message source, but he could not get the real sender. However, MIBAS paid no attention to privacy of the receivers and has not taken the privacy of the receivers into account during its design. Our analyses show that there widely exist the receiver privacy exposure and decryption unfairness problems in the existing multi-receiver ID-based signcryption schemes. Motivated by these concerns, a new multi-receiver ID-based anonymous signcryption (nMIBAS) is proposed to protect the identity of the receivers. The nMIBAS scheme can not only solve the problem that the existing schemes cannot protect the privacy of receivers, but also meet the fairness of decryption to prevent the possible cheating behavior of the sender effectively. Analysis shows that this scheme is a secure and effective signcryption scheme

Lightweight certificateless and provably-secure signcryptosystem for the internet of things

International audienceIn this paper, we propose an elliptic curve-based signcryption scheme derived from the standardized signature KCDSA (Korean Certificate-based Digital Signature Algorithm) in the context of the Internet of Things. Our solution has several advantages. First, the scheme is provably secure in the random oracle model. Second, it provides the following security properties: outsider/insider confidentiality and unforgeability; non-repudiation and public verifiability, while being efficient in terms of communication and computation costs. Third, the scheme offers the certificateless feature, so certificates are not needed to verify the user's public keys. For illustration, we conducted experimental evaluation based on a sensor Wismote platform and compared the performance of the proposed scheme to concurrent scheme

Multi-message multi-receiver signcryption scheme based on blockchain

In conventional message communication systems, the practice of multi-message multi-receiver signcryption communication encounters several challenges, including the vulnerability to Key Generation Center (KGC) attacks, privacy breaches and excessive communication data volume. The KGC necessitates a secure channel to transmit partial private keys, thereby rendering the security of these partial private keys reliant on the integrity of the interaction channel. This dependence introduces concerns regarding the confidentiality of the private keys. Our proposal advocates for the substitution of the KGC in traditional certificateless schemes with blockchain and smart contract technology. Parameters are publicly disclosed on the blockchain, leveraging its tamper-proof property to ensure security. Furthermore, this scheme introduces conventional encryption techniques to achieve user identity privacy in the absence of a secure channel, effectively resolving the issue of user identity disclosure inherent in blockchain-based schemes and enhancing communication privacy. Moreover, users utilize smart contract algorithms to generate a portion of the encrypted private key, thereby minimizing the possibility of third-party attacks. In this paper, the scheme exhibits resilience against various attacks, including KGC leakage attacks, internal privilege attacks, replay attacks, distributed denial of service attacks and Man-in-the-Middle (MITM) attacks. Additionally, it possesses desirable security attributes such as key escrow security and non-repudiation. The proposed scheme has been theoretically and experimentally analyzed under the random oracle model, based on the computational Diffie-Hellman problem and the discrete logarithm problem. It has been proven to possess confidentiality and unforgeability. Compared with similar schemes, our scheme has lower computational cost and shorter ciphertext length. It has obvious advantages in communication and time overhead

A Multireceiver Certificateless Signcryption (MCLS) Scheme

User authentication and message confidentiality are the basic security requirements of high-end applications such as multicast communication and distributed systems. Several efficient signature-then-encrypt cryptographic schemes have been proposed to offer these security requirements with lower computational cost and communication overhead. However, signature-then-encryption techniques take more computation time than signcryption techniques. Signcryption accomplishes both digital signature and public key encryption functions in a single logical step and at a much lower cost than ``signature followed by encryption.\u27\u27 Several signcryption schemes based on bilinear pairing operations have been proposed. Similarly, anonymous multi-receiver encryption has recently risen in prominence in multicast communication and distributed settings, where the same messages are sent to several receivers but the identity of each receiver should remain private. Anonymous multi-receiver encryption allows a receiver to obtain the plaintext by decrypting the ciphertext using their own private key, while their identity is kept secret to anyone, including other receivers. Among the Certificateless Multi-receiver Encryption (CLMRE) schemes that have been introduced, Hung et al. proposed an efficient Anonymous Multireceiver Certificateless Encryption (AMCLE) scheme ensuring confidentiality and anonymity based on bilinear pairings and is secure against IND-CCA and ANON-CCA. In this paper, we substantially extend Hung et al.’s multireceiver certificateless encryption scheme to a Multireceiver Certificateless Signcryption (MCLS) scheme that provides confidentiality along with authentication. We show that, as compared to Hung et al.’s encryption scheme, our signcryption scheme requires only three additional multiplication operations for signcryption and unsigncryption phases. Whereas, the signcryption cost is linear with the number of designated receivers while the unsigncryption cost remains constant for each designated receiver. We compare the results with other existing single receiver and multireceiver signcryption schemes in terms of number of operations, exemption of key escrow problem, and public key settings. The scheme proposed in this paper is more efficient for single and multireceiver signcryption schemes while providing exemption from the key escrow problem, and working in certificateless public key settings

On the Provable Security of Multi-Receiver Signcryption Schemes

In ATC 2007, an identity based signcryption scheme for multiple receivers was proposed by Yu et al. In this paper, we first show that Yu et al.\u27s signcryption scheme is insecure by demonstrating an universal forgeability attack - anyone can generate a valid signcryption on any message on behalf of any legal user for any set of legal receivers without knowing the secret keys of the legal users. Also, we point out a subtle flaw in the proof of confidentiality given by Yu et al. and show that the scheme does not provide confidentiality. Further, we propose a corrected version of Yu et al.\u27s scheme and formally prove its security (confidentiality and unforgeability) under the existing security model for signcryption.\\ In another direction, Fagen Li et al. have proposed a pairing based multi-recipient signcryption scheme which works in public key infrastructure (PKI). We show that, the scheme proposed by Fagen Li et al. is not adaptive chosen ciphertext secure. We propose a new PKI based multi-receiver signcryption scheme and formally prove confidentiality and unforgeability of the scheme. Since all the previously reported schemes are shown to have flaws either in this paper or else where, the schemes reported in this paper are the only correct and efficient ones (both identity based and PKI based) for multi-receiver signcryption