Cross-Cloud Federation (CCF) is beneficial for heterogeneous Cloud Service Providers (CSPs) for leasing additional resources from each other. Despite the benefits of on-demand scalability and enhanced service footprints for better service quality, the adoption of CCF is however mainly hindered due to the lack of a comprehensive trust model. The basic aim of such a model should be to address the security and performance concerns of a home CSP on its foreign peers before placing its users’ data and applications in their premises. A transitivity of users’ trust on home CSP and home CSP's trust on its foreign CSPs marks the uniqueness of trust paradigm in CCF. Addressing the concerns of cloud-to-cloud trust paradigm is inevitable to achieve users’ trust in a federation. Various trust models have been proposed in literature for conventional and multi-cloud computing environments. They focus on user requirements but none on federation perspective. Their applicability to CCF for addressing the concerns of cloud-to-cloud trust paradigm requires further consideration. For this reason, we have first outlined the general characteristics of CCF as being dynamic, multi-level and heterogeneous. Afterwards, cloud-to-cloud trust paradigm is proposed based on a set of unique principles identified as (i) trust bi-directionality, (ii) trust composition, (iii) delegation control, and (iv) Resource awareness. An insightful review of Trust Management Systems (TMS) proposed in literature reveals their shortcomings in addressing the requirements of cloud-to-cloud trust paradigm. To overcome these shortcomings, we suggest that some challenges can be merely addressed by aligning the existing methods to the nature of CCF. The remaining challenges require entirely new mechanisms to be introduced. A demonstration of this concept is presented in the form of a requirement matrix suggesting how the characteristics and properties of both CCF and the TMS are influenced by each other. This requirement matrix reveals the potential avenues of research for a TMS aimed specifically for CCF.

With each passing day, the information and communication technologies are evolving with more and more information shared across the globe using the internet superhighway. The threats to information, while connected to the cyber world are getting more targeted, voluminous, and sophisticated requiring new antifragile and resilient network security mechanisms. Whether the information is being processed in the application, in transit within the network or residing in the storage, it is equally susceptible to attack at every level of abstraction and cannot be handled in isolation as the case has been with conventional security mechanisms. The advent of Software-Defined Networks (SDN) has given a new outlook to information protection, where the network can aid in the design of a system that is secure and dependable in case of cyber threats. The nature of SDN, mainly its programmability and centrality of network information and control has led us to think of security in an antifragile per- Pak-UK Institute of Innovative Technologies for Disaster Management, University of Gujrat, Gujrat, Pakistan spective. Our networks can now thrive and grow stronger when they are exposed to volatility by overwhelming cyber threats. However, SDN infrastructure itself is susceptible to severe threats that may mutilate the provision of its usability as security provider. Both these perspectives of "Security with SDN" and "Security for SDN" have invited research and innovations, yet both these approaches remain disintegrated, failing to support each other. The contribution of this paper is threefold, with first reviewing the current state of the art work for both perspectives of SDN security. Second, it advocates the necessity and introduces a novel approach of antifragile cyber security within SDN paradigm and finally it proposes a unified model for integrating both approaches of "Security with SDN" and "Security for SDN" to achieve the overall objective of protecting our information from cyber threats in this globally connected internetwork.

Cloud federation enables inter-layer resource exchanges among multiple, heterogeneous cloud service providers. This article proposes a Quality of Service (QoS) aware trust model for effective resource allocation in response to the various user requests within the Clouds4Coordination (C4C) federation system. This QoS mainly comprises of nine parameters combined into three categories: (i) node profile, (ii) reliability, and (iii) competence. Numerical values for these parameters are computed every 't' seconds for each cloud provider. All values measured over an interval Δt are further processed by the proposed model to evaluate the utility associated with a provider (referred to as a discipline in the presented case study). The decision about interacting with a discipline in a collaborative project is based on this utility value. The systems architecture, evaluation methodology, proposed model, and experimental evaluation on a practical test bed is outlined. The proposed QoS-aware trust evaluation mechanism allows selection of the most useful (based on a utility value) providers. The proposed approach can be used to support federation of cloud services across a number of different application domains.