Key exchange protocols enable two parties to communicate securely over an untrusted network by exchanging a shared secret among them.Authentication and privacy are the two primary objectives of network security where privacy ensures that transmitted messages cannot eavesdrop.On the other hand, authentication assures that no unauthorized user can gain access maliciously.These two goals can be achieved simultaneously, using authenticated key exchange scheme where two or more parties can share a common secret to transmit a message securely in an open network.Abundant work has been done in 3PAKErelevant to password-based authentication, traditional public key cryptosystem (PKC) and without server's public key Research
Key exchange protocols enable two parties to communicate securely over an untrusted network by exchanging a shared secret among them.Authentication and privacy are the two primary objectives of network security where privacy ensures that transmitted messages cannot eavesdrop.On the other hand, authentication assures that no unauthorized user can gain access maliciously.These two goals can be achieved simultaneously, using authenticated key exchange scheme where two or more parties can share a common secret to transmit a message securely in an open network.Abundant work has been done in 3PAKErelevant to password-based authentication, traditional public key cryptosystem (PKC) and without server's public key Research
With the advancement in Internet-based technologies, network applications are no longer just limited to one-to-one communication; instead, it has become a publicly accessible resource. Regardless of this growth, such applications bring specific challenges concerning authentication, integrity, and privacy. Cryptography stands as an ideal solution to overcome these issues through an interactive method of secure communication called Key Exchange. Key exchange protocols allow two or more entities to agree upon a shared secret transmitted over a public channel without revealing any information to an eavesdropper.
This thesis contributes to the design and analysis of the variants of key exchange protocols along with their applications. As per the security requirements, the proposed schemes are either designed in an interactive model or a non-interactive model. Each scheme undergoes a series of formal and informal security analysis. The formal analysis provides simulation result using cryptographic models. Whereas, an informal analysis showcases the theoretical proves on known attacks where an adversary controls the network. The performance analysis maps the protocol’s efficiency based on the computation cost and communication size.
The first contribution introduces an interactive two-party authenticated key exchange protocol. We begin by investigating the security flaws in an existing system such as, lack of user anonymity, trace attack, clogging attack, and failure to resist replay attack. Then proposed an authenticated self-certified key exchange protocol that overcomes the addressed issues. Also, it eliminates the requirements of a trusted certificate authority to authorize the entities. The scheme achieves anonymity during session execution, mutual authentication and enables session key agreement.Based on the ideology, an application is designed, forsecure communication between ad-hoc nodes in a mobile ad-hoc network.
The second contribution contributes to the design of an Identity-based authenticated three-party key exchange protocol that overcomes the incapability of managing huge
peer-to-peer communication and high computation cost faced by two-party authenticated key exchange protocols. The proposed scheme preserves user privacy by enabling the property of anonymity and ensures non-repudiation. Based on the ideology, an application is designed to establish a secure session key between two users with the help of a trusted server for an electronic payment system.
The third contribution proposes an interactive pairing-free certificateless authenticated group key agreement scheme suitable for a resource constrained mobile network. The scheme allows any user to join or leave the group dynamically. The key agreement protocol devised in this scheme ensures un-deniability property by incorporating the signcryption, and unsigncryption algorithm.
The final contribution presents a non-interactive Identity-based deniable authentication protocol that allows an intended receiver to identify the origin of a given message without being able to prove sender’s identity to a third party.
Key agreement protocols are used to establish common keys between two or more entities. The established key can then be used to assure confidentiality of exchanged messages through encryption. Additionally, authenticated key agreement protocols offer implicit authentication. In this paper, new authenticated key agreement protocols are proposed and their security properties are investigated. We start by examining the two-party case and then develop extensions to three parties as well as extensions to any group of k parties. The proposed protocols try to keep exchanged messages and computations minimal, while offering adequate security guarantees. Finally, we develop a variant of our multi-party key agreement protocol tailored for secure group communications among mobile devices.
Key exchange protocols, first introduced by Diffie and Hellman in 1976, are one of the most widely-deployed cryptographic protocols. They allow two parties, that have never interacted before, to establish shared secrets. These shared cryptographic keys may subsequently be used to establish a secure communication channel. Use cases include the classic client-server setting that is for example at play when browsing the internet, but also chats via end-to-end-encrypted instant messaging applications. Security-wise, we generally demand of key exchange protocols to achieve key secrecy and authentication. While, informally, authentication ensures that the communicating parties have confidence in the identity of their peers, key secrecy ensures that any shared cryptographic key that is established via the key exchange protocol is only known to the participants in the protocol and can be used securely in cryptographic protocols, i.e., is sufficiently random. In 1993, Bellare and Rogaway gave a first formalization of key exchange protocol security that captures these properties with respect to powerful adversaries with full control over the network. Their model constitutes the basis of the many subsequent treatments of authenticated key exchange security, including the models presented in this thesis. The common methodological approach underlying all of these formalizations is the provable security paradigm, which has become a standard tool in assessing the security of cryptographic protocols and primitives. So-called security models specify the expected security guarantees of the scheme in question with regards to a well-defined class of adversaries. Proofs that validate these security claims do so by reducing the security of the overall scheme to the security of the underlying cryptographic primitives and hardness assumptions. However, advances in computational power and more sophisticated cryptanalytic capabilities often render exactly these components insecure. Especially the advent of quantum computers will have a devastating effect on much of today's public key cryptography. This is especially true for key exchange protocols since they rely crucially on public-key algorithms. In this thesis, our focus in future-proofing key exchange protocols is two-fold. First, we focus on extending security models for key exchange protocols to capture the (un)expected break of cryptographic primitives and hardness assumptions. The aim is to gain assurances with respect to future adversaries and to investigate the effects of primitive failures on key exchange protocols. More specifically, we explore how key exchange protocols can be safely transitioned to new, post-quantum secure algorithms with hybrid techniques. Hybrids combine classical and post-quantum algorithms such that the overall key agreement scheme remains secure as long as one of the two base schemes remains secure. For this, we introduce security notions for key encapsulation mechanisms that account for adversaries with varying levels of quantum capabilities and present three new constructions for hybrid key encapsulation mechanisms. Our hybrid designs are practice-inspired and for example capture draft proposals for hybrid modes in the Transport Layer Security (TLS) protocol, which is one of the most widely-deployed cryptographic protocols that enables key agreement. Furthermore, our notion of breakdown resilience for key exchange protocols allows to gauge the security of past session keys in the event of a failure of a cryptographic component in the key exchange. We exercise our model on variants of the post-quantum secure key exchange protocol NewHope by Alkim et al. Thereby, we confirm the intuition that, in order to guard against adversaries that only have access to quantum computing power in the (more distant) future, it is sufficient to use classically-secure authentication mechanisms alongside post-quantum key agreement to achieve authenticated key exchange. As with any mathematical statement, theorems in the provable security paradigm are only as valid as the underlying assumptions. A careful consideration of any newly made assumption is thus essential to ensure the meaningfulness of the statement itself and make the assumption a viable tool for future analyses. Thus, secondly, we systematically classify the PRF-ODH assumption, a complexity-theoretic hardness assumption that has been used in key exchange security analyses of such prominent protocols as TLS, Signal, and Wireguard. In particular, we give a unified, parametrized definition of the assumption encompassing different variants that are present in the literature. We relate the resulting parametrized notions in terms of their strength and show where these assumptions fit in the collection of well-understood related hardness assumptions. We finally sketch our result on the impossibility of instantiating this assumption in the standard model, thereby disposing of the uncertainty in the community whether PRF-ODH is in fact a standard model assumption, i.e., removes the usage of some idealized assumptions in key exchange protocol proofs.
To ensure resistance to attacks with coercion to disclose a secret key by an active adversary, the protocol of deniable encryption includes a procedure for mutual authentication of the sender and receiver of a message with their long-term public keys, which is combined with a hidden exchange of single-use public keys used to generate a single-use shared key, on which the secret message is encrypted. Longterm public keys are used to generate a shared secret key, on which a fake message is encrypted. The produced intermediate ciphertexts are converted into a single ciphertext, which is computationally indistinguishable from the ciphertext obtained by probabilistic encryption of a fake message. This approach allows us to build an encryption protocol that is resistant to bi-sided attacks with coercion, since the disclosure of users' private keys gives access only to the fake message and cannot be used to prove the possibility of alternative decryption of the ciphertext transmitted over a public communication channel. The authentication of the single-use public keys is also used to implement protocols for secure encryption using short shared keys.
Since for the e-business development, users sometimes need to share sensitive personal information through a public network, they do not want their privacy information revealed by the malicious attackers. In 2007, LaMacchia et al. proposed a two-party authentication key exchange (2PAKE) protocol under the security assumption of extended Canetti-Krawczyk (ECK) model. Although the ECK model is well designed to guarantee security in a two-party key exchange, it is not suitable in several other real situations with more parties, such as in auction, space communication, and internet of things (IoT), among others. Considering these problems, we first propose several ECK-based three-party authentication key exchange protocols, which provide personal privacy security protection and increase the usability of the authentication key exchange protocols. We also discuss three cases in different application environments. Moreover, the pairing operations are used in some cases if the application situations require less communication steps.
Authenticated key-exchange protocols allow two participants A and B , communicating over a public network and each holding an authentication means to exchange a shared secret value. Methods designed to deal with this cryptographic problem ensure A (resp. B ) that no other participants aside from B (resp. A ) can learn any information about the agreed value and often also ensure A and B that their respective partner has actually computed this value. A natural extension to this cryptographic method is to consider a pool of participants exchanging a shared secret value and to provide a formal treatment for it. Starting from the famous two-party Diffie--Hellman (DH) key-exchange protocol and from its authenticated variants, security experts have extended it to the multiparty setting for over a decade and, in the past few years, completed a formal analysis in the framework of modern cryptography. The present paper synthesizes this body of work on the provably-secure authenticated group DH key exchange.