IEEE SmartWorld, Ubiquitous Intelligence & Computing, Advanced & Trusted Computing, Scalable Computing & Communications, Cloud & Big Data Computing, Internet of People and Smart City Innovation (SmartWorld/SCALCOM/UIC/ATC/CBDCom/IOP/SCI)
Primitive Constituent Elements of Cryptographic Protocols
Many cryptographic protocols have been proposed, and many studies of them have been done. However, there is no study to identify constituent elements of cryptographic protocols that are elements of the protocols consist of. The constituent elements can be used for the basis of classification of already proposed cryptographic protocols, the basis of prediction of new cryptographic protocols, and the basis of formal verification for cryptographic protocols. This paper presents primitive constituent element of cryptographic protocols that is an element so that cryptographic protocol cannot accomplish its original tasks without it.
Many cryptographic protocols have been proposed, and many studies of them have been done. However, there is no study to identify constituent elements of cryptographic protocols that are elements of the protocols consist of. The constituent elements can be used for the basis of classification of already proposed cryptographic protocols, the basis of prediction of new cryptographic protocols, and the basis of formal verification for cryptographic protocols. This paper presents primitive constituent element of cryptographic protocols that is an element so that cryptographic protocol cannot accomplish its original tasks without it.
The methods of cryptography can be successful only if they are properly incorporated into an application. A cryptographic technique can be unbreakable as such, and yet could still be insecure if it is used unwisely. This observation motivates the subject of security protocols. A security protocol consists of a formal method of using a cryptographic technique in a practical application. Without a well-defined security protocol, a perfectly secure cryptographic technique could be compromised by its use. We do not draw a sharp distinction between the topic of secrecy and the topic of security. The two are closely related, and it is not helpful to attempt to draw a sharp line between them. In this context, a primitive is a basic method of obtaining secrecy and a protocol is a body of rules for using that primitive. In this chapter we will also study other forms of information protection such as identification and secret sharing that can be regarded as topics closely related to security protocols. The topic of identification deals with methods for establishing the identity of the source of a transmission. This is a subtle and difficult topic because the very concept of identity is vague and subjective. The identity of an isolated individual or device may be self-defined and subject to no outside verification. That identity is useful only to establish that all messages in a sequence of messages are from the same entity.
This paper summarizes the current knowledge in the field of two-party cryptographic protocols devised from quantum systems. We introduce the reader to the notion of cryptographic protocols and describe a number of simple building blocks to achieve them. We also give pointers for the reader who is interested to the quantum implementation of these building blocks. 1 Introduction Since the 1970's the science of secret writing, cryptography, has changed substantially due to the introduction of "public key cryptosystems" [26, 41]. The many properties of certain instances of these systems have open the door to several new applications (consult [42, 25, 29, 44, 34, 28, 7, 30, 36, 32, 11, 19, 33] for instance, to mention just a few). The initial goal of cryptography, to provide secure communications, has evolved into a variety of tasks involving secret data. The scenario in which such tasks take place involves two participants (say Alice and Bob) who wish to perform some computation involving ...
This chapter discusses cryptographic protocols, which provide a means for cryptographic primitives to be combined in ways that allow complex sets of security goals to be tailored to particular application environments. It describes a simple, but artificial, application in order to demonstrate that there are many different ways in which a cryptographic protocol can be designed, and also how sensitive the security of cryptographic protocols can be. It then considers the important family of AKE protocols (authentication and key establishment).
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.
We develop an approach to deriving concrete engineering advice for cryptographic protocols from provable-security-style proofs of security. The approach is illustrated with a simple, yet useful protocol. Our main result provides the first published proof of an exact probabilistic relationship betwe en a high-level protocol and multiple cryptographic primitives. This exact relationship enables us to rigorously derive concrete recommendations on the bitlengths of cryptographic keys and on how often principals should rekey. As an additional benefit of our approach, the process of developing our theorem and proof lead us to identify and implement an improvement in our example protocol.
[EN] With the arrival of quantum computing, ensuring the security of communications protocol has become even more crucial. This study explores the formal verification of a Transport Layer Security protocol designed to withstand quantum menaces. While traditional cryptographic methods are effective against classical computing adversaries, they are susceptible to attacks empowered by quantum computation. Hence, there is a real need to transition to Post-Quantum cryptography, which offers resilience against future threats. This research focuses on formally veryfiying the Hybrid Post-Quantum TLS protocol to provide mathematical assurance of its security properties. Formal verification offers a rigorous method for analyzing the correctness and robustness of cryptographic protocols, reducing the risk of undetected vulnerabilities. By employing formal methods, we scrutinize the protocol s design, implementation, and cryptographic primitives to identify a potential weaknesses and ensure compliance with security standards. The formal verification of the Hybrid Post-Quantum TLS protocol not only enhances our understanding of its security assurances but also underscores the significance of rigorous validation in cryptographic design.