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By side-channel attacks, a fraction part of secret keys used in cryptographic schemes could be leaked to adversaries. Recently, adversaries have realized practical side-channel attacks so that these existing cryptographic schemes could be broken. Indeed, researchers have invested and proposed a good approach to withstand such attacks, called as leakage-resilient cryptography. Very recently, several leakage-resilient anonymous multi-receiver encryption (LR-AMRE) schemes based on various public-key systems were also proposed. However, these LR-AMRE schemes are not suitable for a heterogeneous public-key environment under which an authorized receiver group includes heterogeneous receivers under various PKS settings and these receivers have various types of secret/public key pairs. In this article, we propose the $first$ leakage-resilient anonymous heterogeneous multi-receiver hybrid encryption (LR-AHMR-HE) scheme for the heterogeneous public-key system settings. A new framework and associated adversary games of the LR-AHMR-HE scheme are defined. In the adversary games, adversaries are admitted to continuously intercept a fraction part of secret keys. Under the adversary games, formal security proofs are provided to show that the proposed scheme is secure against two types of adversaries (illegitimate user and malicious authority). Comparisons with several related previous schemes are demonstrated to present the merits of our scheme.

Key encapsulation schemes in public key system (PKS) can be used to protect sensitive or private data. Unlike traditional PKS and identity-based PKS, certificate-based PKS (CB-PKS) not only avoids the establishment of complex public key infrastructures, but also does not encounter the key escrow problem. Anonymous multi-receiver certificate-based encryption (AMR-CBE) or anonymous multi-receiver certificate-based key encapsulation (AMR-CB-KE) scheme enables a sender to use multiple receivers’ public keys to perform one-time encryption process for a message and send the encrypted ciphertext to these receivers, while these receivers do not know the other receiver’s identity. However, the existing AMR-CBE and AMR-CB-KE schemes cannot resist side-channel attacks. Attackers with the ability of such attacks can continuously obtain part (several bits) of the secret keys and then calculate the complete secret keys. In such a case, such attacks make a cryptographic scheme (including AMR-CBE and AMR-CB-KE schemes) insecure. Leakage-resilient cryptography is an important research topic to resist side-channel attacks. In this paper, we propose the first leakage-resilient anonymous multi-receiver certificate-based key encapsulation (LR-AMR-CB-KE) scheme. Based on the discrete logarithm and hash function assumptions, we demonstrate the scheme has the indistinguishability of two ciphertexts against chosen ciphertext attacks (IND-CCA) and the anonymous indistinguishability of two identities against chosen ciphertext attacks (ANON-IND-CCA) for two types of attackers in CB-PKS settings.

Signature can be used to verify the integrity of both a message and the identity of a signer, whereas encryption can be used to ensure the confidentiality of a message. In the past, cryptography researchers have studied and proposed numerous certificateless signcryption (CLSC) schemes to combine the benefits of both signature and encryption. However, these schemes may not be robust enough to withstand side-channel attacks. Through such attacks, an attacker can constantly retrieve a portion of a private key of the system, and could eventually recover the entire private key. Leakage-resilient certificateless signcryption (LR-CLSC) can ensure its security when the attacker launches such attacks. As far as we know, the existing LR-CLSC schemes can only guarantee the security under a bounded leakage model, where the portion of the private key that an attacker can obtain through side-channel attacks is limited. In this paper, we propose the $first$ LR-CLSC scheme under a continual leakage model. Also, we demonstrate the proposed scheme is secure for the existential unforgeability and the ciphertexts indistinguishability against attackers with side-channel attacking abilities.

Certificate-based public key cryptography (CB-PKC) removes the problem of certificate management in traditional public key systems and avoids the key escrow problem in identity-based public key systems. In the past, many authenticated key exchange (AKE) protocols based on CB-PKC systems, called CB-AKE, were proposed to be applied to secure communications between two remote participants. However, these existing CB-AKE protocols become insecure since attackers could compute and obtain the whole secret key from some partial leaked information of the secret key by side channel attacks. In this paper, our goal is to propose the $first$ CB-AKE protocol with the property to resist side channel attacks, called leakage-resilient CB-AKE (LR-CB-AKE). The proposed LR-CB-AKE protocol is formally proven to be secure in the generic bilinear group (GBG) model under the discrete logarithm (DL) and computational Diffie-Hellman (CDH) assumptions.

A multi-recipient signcryption (MRSC) scheme possesses the functionalities of both multi-recipient public-key encryption and digital signature to ensure both integrity and confidentiality of transmitted messages. Moreover, an anonymous MRSC (AMRSC) scheme retains the functionalities of an MRSC scheme while offering privacy-preserving, namely, a recipient’s identity or public key being hidden to other recipients. In the past, numerous MRSC and AMRSC schemes based on various public-key cryptographies (i.e., public key infrastructure (PKI)-based, identity (ID)-based and certificateless (CL)) were proposed. Recently, an attacker can realize side-channel attacks to acquire partial bits of private keys participated in cryptographic computations. However, up to date, no MRSC or AMRSC scheme can resist side-channel attacks so that these schemes might suffer from such attacks and could be broken. To resist such attacks under a continual leakage model, we propose the $first$ PKI-based leakage-resilient AMRSC (PKI-LR-AMRSC) scheme in this paper. In the proposed scheme, an attacker is permitted to continually acquire partial bits of private keys partook in computations of the PKI-LR-AMRSC scheme, and formal security proofs are given to show that the proposed scheme still retains the original security of AMRSC schemes. As compared with the relevant AMRSC schemes, our PKI-LR-AMRSC scheme not only resists side-channel attacks but also reduces the cost of executing the multi-signcryption and unsigncryption algorithms. In particular, the point is that the computational complexities of our scheme respectively require only $O(t)$ and $O(1)$ in executing the Multi-signcryption algorithm and the Unsigncryption algorithm, where $t$ is the number of recipients.

Establishing a session key (SSK) is very important for real-world deployment in open networks, which enables secure communication between remote parties. In the past, some authenticated key exchange (AKE) protocols have been proposed to generate a SSK, but the certificate management issue is inhered in the traditional public key infrastructure and must be addressed. To tackle this issue, the identity (ID)-based concept is added to AKE, called ID-AKE. Indeed, the security of the existing AKE/ID-AKE protocols is gaining increasing importance due to some new types of attacks, namely, side-channel attacks. In such attacks, adversaries could obtain secret keys’ partial information during the execution of cryptographic protocols (including AKE/ID-AKE). To withstand such attacks, many leakage-resilient ID-AKE (LR-ID-AKE) protocols resisting side-channel attacks have been proposed. However, these existing LR-ID-AKE protocols have no efficient solution to revoke compromised users. In this article, the first LR-ID-AKE protocol with an efficient revocation mechanism, called LR-RID-AKE, is proposed. The proposed protocol is not only as secure as existing LR-ID-AKE protocols but also able to efficiently revoke compromised users from the system.

Certificateless public-key cryptography has conquered both the certificate management problem in the traditional public-key cryptography and the key escrow problem in the ID-based public-key cryptography. Certificateless authenticated key exchange (CLAKE) protocol is an important primitive of the certificateless public-key cryptography. A CLAKE protocol is employed to provide both mutual authentication and establishing a session key between two participators. Indeed, all conventional public-key cryptographies have encountered a new kind of attack, named “side-channel attacks”. Fortunately, leakage-resilient cryptography is a flexible approach to withstand such attacks. However, the design of leakage-resilient CLAKE (LR-CLAKE) protocols is not studied. In the article, by extending the well-known extended-Canetti-Krawczyk (eCK) model, we present the security notions (adversary model) of LR-CLAKE protocols, called continual-leakage-resilient eCK (CLReCK) model. The first LR-CLAKE protocol withstanding side-channel attacks is proposed. By employing the proof technique of the generic bilinear group (GBG) model, we formally prove the security of our protocol in the CLReCK model.

In the past, the security of most public-key encryption or key encapsulation schemes is shown in an ideal model, where private keys, secret keys and random values are assumed to be absolutely secure to adversaries. However, this ideal model is not practical due to side-channel attacks in the sense that adversaries could gain partial information of these secret values involved in decryption operations by perceiving energy consumption or execution timing. In such a case, these schemes under the ideal model could suffer from side-channel attacks. Recently, leakage-resilient cryptography resistant to side-channel attacks is an emerging research topic. Certificate-based encryption (CBE) or certificate-based key encapsulation (CB-KE) schemes are a class of important public-key encryption. However, little work addresses the design of leakage-resilient CBE (LR-CBE) or leakage-resilient CB-KE (LR-CB-KE) schemes. In this paper, we present the first LR-CB-KE scheme with overall unbounded leakage property which permits adversaries to continuously gain partial information of the system secret key of a trusted certificate authority (CA), the private keys and certificates of users, and random values. In the generic bilinear group model, formal security analysis is made to prove that the proposed LR-CB-KE scheme is secure against chosen ciphertext attacks.

Certificate-based cryptography is an attractive public-key setting, and it not only simplifies certificate management in the traditional public-key cryptography but also eliminates the key escrow problem inherent in the identity-based cryptography. Recently, leakage-resilient cryptography resistant to side-channel attacks has received significant attention from cryptographic researchers. By side-channel attacks, adversaries could obtain partial information of secret and private keys involved in cryptographic algorithms by perceiving execution time or energy consumptions of each algorithm invocation. The certificate-based signature (CBS) is a class of important public-key signature. Up to date, there exists no leakage-resilient CBS (LR-CBS) scheme resistant to side-channel attacks. In this paper, the first LR-CBS scheme is proposed and it possesses overall unbounded leakage property, namely, it permits adversaries to continuously obtain partial information of secret or private keys involved in the associated algorithm invocations. The security analysis is given to prove that the proposed LR-CBS scheme is existential unforgeability against adaptive chosen-message attacks for adversaries in the generic bilinear group model.

Based on users’ permanent private keys and ephemeral secret keys (randomness secret values), authenticated key agreement (AKA) protocols are used to construct a common session key between two session parties while authenticating each other. Recently, the design of leakage-resilient AKA (LR-AKA) resisting side-channel attacks has received significant attention from researchers. By side-channel attacks, an adversary is allowed to obtain fractional leakage information of private (secret) keys during the computation rounds of LR-AKA protocols. However, most LR-AKA protocols have a restriction, namely, the overall fractional leakage information must be bounded. In this paper, we propose an efficient LR-AKA protocol with overall unbounded leakage property in the continual leakage extended Canetti-Krawczyk model. Security analysis is given to demonstrate that our LR-AKA protocol is provably secure in the generic bilinear group model. By comparisons, our protocol is better than the previously proposed LR-AKA protocols in terms of computation cost, security model, and leakage properties.

In a smart city, there are different types of entities, such as nature persons, IoT devices, and service providers, which have different computational limitations and storage limitations. Unfortunately, all of the existing authentication and key exchange (AKE) protocols are designed for either client–server or client–client authentication, including the ones designed for smart cities. In this paper, we present the idea of a compatible authentication and key exchange (CAKE) protocol which provides cross-species authentication. We propose the first CAKE protocol for a smart city that any two valid entities can authenticate with each other and create a secure session key without the help of any third party, while there is also no password table and no public key issuing problem. The entity can be a natural person having biometrics, an IoT device embedded with a physical unclonable function (PUF), or a service provider. Moreover, we extend the CAKE protocol to an anonymous CAKE (ACAKE) protocol, which provides natural persons an anonymous option to protect their privacy. In addition, both the proposed CAKE and ACAKE protocols can deal with the entity revocation problem. We define the framework and the security model of CAKE and ACAKE protocols. Under the security model, we formally prove that the proposed protocols are secure under the elliptic curve computational Diffie–Hellman (ECCDH) problem, the decisional bilinear Diffie–Hellman (DBDH) problem, and hash function assumptions. Comparisons with the related protocols are conducted to demonstrate the benefits of our protocols. Performance analysis is conducted and the experience results show that the proposed protocols are practical in a smart city.

In cloud storage systems, users can upload their data along with associated tags (authentication information) to cloud storage servers. To ensure the availability and integrity of the outsourced data, provable data possession (PDP) schemes convince verifiers (users or third parties) that the outsourced data stored in the cloud storage server is correct and unchanged. Recently, several PDP schemes with designated verifier (DV-PDP) were proposed to provide the flexibility of arbitrary designated verifier. A designated verifier (private verifier) is trustable and designated by a user to check the integrity of the outsourced data. However, these DV-PDP schemes are either inefficient or insecure under some circumstances. In this paper, we propose the first non-repudiable PDP scheme with designated verifier (DV-NRPDP) to address the non-repudiation issue and resolve possible disputations between users and cloud storage servers. We define the system model, framework and adversary model of DV-NRPDP schemes. Afterward, a concrete DV-NRPDP scheme is presented. Based on the computing discrete logarithm assumption, we formally prove that the proposed DV-NRPDP scheme is secure against several forgery attacks in the random oracle model. Comparisons with the previously proposed schemes are given to demonstrate the advantages of our scheme.

With the rapid development in wireless communications and cloud computing technologies, clients (users) often use handheld mobile devices to access remote servers via open network channels. To provide authentication and confidentiality between clients and servers, a large number of ID-based authentication and key exchange (ID-AKE) protocols have been proposed for mobile client-server environments. However, most of the existing ID-AKE protocols adopt the precomputation technique so that they become vulnerable to the ephemeral-secret-leakage (ESL) attacks, in the sense that an adversary could use the ephemeral secrets to reveal the private keys of clients from the corresponding exchange messages. In the paper, we propose a new ESL-secure ID-AKE protocol for mobile client-server environments. We formally prove that the proposed protocol satisfies the security requirements of both mutual authentication and key exchange while resisting the ESL attacks. When compared with previously proposed ID-AKE protocols, our protocol has higher security and retains computational performance, since it requires no bilinear pairing operation for mobile clients. Finally, we mention the possibility of adopting our protocol as an authentication method of the extensible authentication protocol (EAP) for wireless networks.

Certificateless signatures (CLS) are noticeable because they may resolve the key escrow problem in ID-based signatures and break away the management problem regarding certificate in conventional signatures. However, the security of the mostly previous CLS schemes relies on the difficulty of solving discrete logarithm or large integer factorization problems. These two problems would be solved by quantum computers in the future so that the signature schemes based on them will also become insecure. For post-quantum cryptography, lattice-based cryptography is significant due to its efficiency and security. However, no study on addressing the revocation problem in the existing lattice-based CLS schemes is presented. In this paper, we focus on the revocation issue and present the first revocable CLS (RCLS) scheme over lattices. Based on the short integer solution (SIS) assumption over lattices, the proposed lattice-based RCLS scheme is shown to be existential unforgeability against adaptive chosen message attacks. By performance analysis and comparisons, the proposed lattice-based RCLS scheme is better than the previously proposed lattice-based CLS scheme, in terms of private key size, signature length and the revocation mechanism.

The existence of malicious participants is a major threat for authenticated group key exchange (AGKE) protocols. Typically, there are two detecting ways (passive and active) to resist malicious participants in AGKE protocols. In 2012, the revocable identity- (ID-) based public key system (R-IDPKS) was proposed to solve the revocation problem in the ID-based public key system (IDPKS). Afterwards, based on the R-IDPKS, Wu et al. proposed a revocable ID-based AGKE (RID-AGKE) protocol, which adopted a passive detecting way to resist malicious participants. However, it needs three rounds and cannot identify malicious participants. In this paper, we fuse a noninteractive confirmed computation technique to propose the first two-round RID-AGKE protocol with identifying malicious participants, which is an active detecting way. We demonstrate that our protocol is a provably secure AGKE protocol with forward secrecy and can identify malicious participants. When compared with the recently proposed ID/RID-AGKE protocols, our protocol possesses better performance and more robust security properties.