ASICS: Authenticated Key Exchange Security Incorporating Certification Systems

Most security models for authenticated key exchange (AKE) do not explicitly model the associated certification system, which includes the certification authority and its behaviour. However, there are several well-known and realistic attacks on AKE protocols which exploit various forms of malicious key registration and which therefore lie outside the scope of these models. We provide the first systematic analysis of AKE security incorporating certification systems. We define a family of security models that, in addition to allowing different sets of standard AKE adversary queries, also permit the adversary to register arbitrary bitstrings as keys. For this model family, we prove generic results that enable the design and verification of protocols that achieve security even if some keys have been produced maliciously. Our approach is applicable to a wide range of models and protocols; as a concrete illustration of its power, we apply it to the CMQV protocol in the natural strengthening of the eCK model to the ASICS setting

A Reflection on the Security of Two-Party Key Establishment Protocols

Two-party key establishment has been a very fruitful research area in cryptography, with many security models and numerous protocols proposed. In this paper, we take another look at the YAK protocol and the HMQV protocols and present some extended analysis. Motivated by our analysis, we reflect on the security properties that are desired by two-party key establishment protocols, and their formalizations. In particular, we take into account the interface between a key establishment protocol and the applications which may invoke it, and emphasize the concept of session and the usage of session identifier. Moreover, we show how to design a two-party key establishment protocol to achieve both key authentication and entity authentication properties in our security model

Security in Key Agreement: Two-Party Certificateless Schemes

The main goal of cryptography is to enable secure communication over a public channel; often a secret shared among the communicating parties is used to achieve this. The process by which these parties agree on such a shared secret is called key agreement. In this thesis, we focus on two-party key agreement protocols in the public-key setting and study the various methods used to establish and validate public keys. We pay particular attention to certificateless key agreement schemes and attempt to formalize a relevant notion of security. To that end, we give a possible extension of the existing extended Canetti-Krawzcyk security model applicable to the certificateless setting. We observe that none of the certificateless protocols we have seen in the literature are secure in this model; it is an open question whether such schemes exist. We analyze several published certificateless key agreement protocols, demonstrating the existence of key compromise impersonation attacks and even a man-in-the-middle attack in one case, contrary to the claims of the authors. We also briefly describe weaknesses exhibited by these protocols in the context of our suggested security model

Physical activity and cancer

It is widely accepted that physical activity is important for physical functioning and well-being, and as such the promotion of active lifestyles is becoming increasingly significant in public health policy both in the UK and worldwide. Sedentary lifestyles have been associated with increased risk of obesity and preventable disease including diabetes, coronary heart disease and some cancers. With regards cancer specifically, this chapter will provide a brief overview on current opinions on the link between physical activity and cancer prevention. The published evidence focuses both on primary and secondary prevention. More recent evidence has investigated the use of physical activity in secondary prevention for those who have been diagnosed with cancer and proposed a link between physical activity, morbidity and mortality in those with cancer. The evidence-base for secondary prevention is more limited. Nevertheless, studies to date have indicated that physical activity can improve both physical functioning and psychological outcomes in cancer survivors, and significantly improve quality of life. The exact nature of those interventions which confer the most positive effects is less well-established, and there is a current lack of consensus on the most appropriate type, intensity and duration of activity for people with cancer. It has not yet been well established as to which stage of the treatment programme physical activity should be encouraged (during or following treatment) or the most appropriate length of time during which structured physical activity interventions should be delivered to achieve beneficial results. These factors will be discussed in this chapter, and barriers to engaging in physical activity for those with a diagnosis of cancer will be considered. The chapter will conclude with a summary of key findings and the potential for further research

Analyzing Multi-key Security Degradation

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ProvablySecure Authenticated Group Diffie-Hellman Key Exchange

Abstract: 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 2-party Diffie-Hellman (DH) key exchange protocol, and from its authenticated variants, security experts have extended it to the multi-party setting for over a decade and completed a formal analysis in the framework of modern cryptography in the past few years. The present paper synthesizes this body of work on the provably-secure authenticated group DH key exchange. The present paper revisits and combines the full versions of the following four papers