Blockchain interoperability is an innovative feature of blockchain technology that is rapidly gaining momentum in various fields. The mass adoption of enterprise blockchains has not yet been achieved because blockchain networks act as isolated islands that cannot connect or exchange assets and/or information. In addition, the invocation of smart contracts is restricted only to on-chain executions because of the lack of connectivity between the blockchains. This survey paper aims to conduct a comprehensive and thorough literature review regarding blockchain interoperability, with special highlight on blockchain Oracles being state-of-the-art. Oracles have shown potential as an emerging technology that has revolutionized the blockchain ecosystem by acting as agents that fetch external information into the blockchain ecosystem. A detailed comparative discussion of different blockchain interoperability techniques is presented, showing the strengths and weaknesses of each technique. Being overlooked in the literature, the shortcomings of these techniques in comparison to Oracles are identified, addressing how Oracles have succeeded in overcoming many of these limitations. In addition, the literature lacks a focus on the latest market solutions adopting blockchain Oracles, and only a few studies have considered them in detail. This gap has been addressed through an in-depth assessment of the latest market solutions adopting Oracles in the past few years. Finally, design issues trying to achieve the best practices of Oracles, future directions, and identified research gaps are highlighted. .

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Secure communication in Vehicular Ad hoc Networks (VANETs) can be achieved through a public key infrastructure (PKI). A tamper proof device (TPD) is traditionally used to statically store encryption keys in each vehicle. These keys are renewed periodically by a certificate authority (CA). In this paper, a dynamic key distribution protocol for PKI-based VANETs is proposed. A vehicle dynamically requests a key from its nearest road side unit. This request is securely propagated through network infrastructure to reach a CA cloud and a key is returned. A proposed key revocation mechanism makes use of the enhanced key distribution protocol to reduce the number of messages needed for revocation. Performance analysis has been performed through network simulation to demonstrate that the proposed protocol can dynamically support efficient and cost-reduced key distribution for vehicles.

We used our original Interactive Remote Instruction (IRI) system to teach scores of university classes over the past five years at sites up to 300 km apart. While this system is a prototype, its use in real classes allows us to deal with crucial issues in distributed education instruction systems. We describe our motivation and vision for a reimplementation of IRI that supports synchronous and asynchronous distance education. This new version, called IRI-h (h for heterogeneous), is coded in Java and executes on several different platforms. IRI-h extends IRI both to multiple platforms and heterogeneous network infrastructures, including delivery to home users. In this article we describe IRI-h's architectural experiences with the developing prototype, including preliminary performance evaluation, and also unresolved issues still to be addressed.

In recent years, we have seen the introduction and use of many distance learning systems. Some of these systems are characterized as Interactive which means the dominant mode of instruction is live or synchronous using networked multimedia technology such as audio, video and shared workspaces. In this paper, we present the common features and essential elements that should be implemented in such systems. Throughout this paper, we will use as a model and case study the IRI-h system (for Interactive Remote Instruction-heterogeneous) that we have developed and implemented in Java and have used to support distance learning at Old Dominion University.