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Abstract-Public Key Infrastructure (PKI) is the most widely used security mechanism for securing communications over the network. However, there are known performance issues, making it unsuitable for use in the Vehicular Networks (VNs). In this paper, we propose a Secure and Authenticated Key Management Protocol (SA-KMP) to overcome the shortcomings of the PKI. The SA-KMP scheme distributes repository containing the bindings of the entity's identity and its corresponding public key to each vehicle and Road Side Unit (RSU). By doing so, certificate exchanges and Certificate Revocation Lists (CRLs) are eliminated. Furthermore, SA-KMP scheme uses symmetric keys derived based on a 3D matrix based key agreement scheme to reduce the high computational costs of using asymmetric cryptography. We demonstrate the efficiency of the SA-KMP through performance evaluations in terms of transmission and storage overhead, network latency and key generation time. Analytical results show that the SA-KMP is more scalable and outperforms the certificate based PKI. Simulation results indicate that the key generation time of the SA-KMP scheme is less than that of the existing Elliptic Curve Diffie-Hellman (ECDH) and Diffie-Hellman (DH) protocols. In addition, we use Proverif to prove that the SA-KMP scheme is secure against an active attacker under the Dolev and Yao model and further show that the SA-KMP scheme is secure against Denial of Service (DoS), collusion attacks and a wide range of other malicious attacks.

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Given the increasing number of learners in massive open online courses (MOOCs), students’ self-directed learning (SDL) skills are necessary for their success. The purpose of this study was to explore learners’ motivation for enrolling in MOOCs and their SDL strategies, as well as instructional elements that support SDL from learners’ perspectives. This qualitative study adopted a phenomenological research design. The data source was semi-structured interviews with 15 learners from three MOOCs. The data were analyzed using thematic analysis. The researchers found that the motivation for enrolling in MOOCs included intrinsic motivation (e.g., curiosity, improving personal knowledge, and personal interest) and extrinsic motivation (e.g., supporting formal education and career development). The learning strategies used by MOOC learners were task strategies, self-monitoring, and self-management strategies. The task strategies included taking notes, reading texts or subtitles, watching videos, and conducting further research. The self-monitoring strategies included self-assessment, self-reflection, progress indicators, final projects, and authentic tasks. Learners’ self-management strategies (e.g., time management and resource management) varied depending on their diverse motivations. In addition, the instructional elements that support SDL were self-assessment and discussion forums, instructor feedback, flexibility, clearly stated learning goals, the authenticity of the content, and small learning units. The implications of the study are discussed in the paper.

In this paper we study the correlations that exist between the required transmission power of RTS, CTS, DATA and ACK frames to guarantee a successful 4-way handshake in wireless ad hoc networks based on the IEEE 802.11 distributed coordination function (DCF). From these correlations, and starting from a set of different initial conditions, we can derive a class of power controlled media access control (MAC) algorithms for single channel ad hoc networks based on the existing IEEE 802.11 DCF. From substantial simulations of the different algorithms and comparison to some prominent alternatives, we come to a conclusion that contradicts the intuitively sound, commonly held belief which states that sending control frames at maximum power -to reduce interference on the long data frames -then, the ensuing long data frames at a lower, yet sufficient power level decreases power consumption per carried bit.Index Terms-Ad hoc networks, media access control, power control.