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Autonomous vehicles offer various advantages to both vehicle owners and automobile companies. However, despite the advantages, there are various risks associated with these vehicles. These vehicles interact with each other by forming a vehicular network, also known as VANET, in a centralized manner. This centralized network is vulnerable to cyber-attacks which can cause data loss, resulting in road accidents. Thus, to prevent the vehicular network from being attacked and to prevent the privacy of the data, key management is used. However, key management alone over a centralized network is not effective in ensuring data integrity in a vehicular network. To resolve this issue, various studies have introduced a blockchain-based approach and enabled key management over a decentralized network. This technique is also found effective in ensuring the privacy of all the stakeholders involved in a vehicular network. Furthermore, a blockchain-based key management system can also help in storing a large amount of data over a distributed network, which can encourage a faster exchange of information between vehicles in a network. However, there are certain limitations of blockchain technology that may affect the efficient working of autonomous vehicles. Most of the existing blockchain-based systems are implemented over Ethereum or Bitcoin. The transaction-processing capability of these blockchains is in the range of 5 to 20 transactions per second, whereas hashgraphs are capable of processing thousands of transactions per second as the data are processed exponentially. Furthermore, a hashgraph prevents the user from altering the order of the transactions being processed, and they do not need high computational powers to operate, which may help in reducing the overall cost of the system. Due to the advantages offered by a hashgraph, an advanced key management framework based on a hashgraph for secure communication between the vehicles is suggested in this paper. The framework is developed using the concept of Leaving of Vehicles based on a Logical Key Hierarchy (LKH) and Batch Rekeying. The system is tested and compared with other closely related systems on the basis of the transaction compilation time and change in traffic rates. [ABSTRACT FROM AUTHOR]

Abstract: Secure multicast applications of multimedia contents, such as Internet TV, pay per view, satellite TV, etc., need to maintain a high number of keys. In these applications, a user contracts a group of channels or even specific content (films, sports, etc.) which do not have to coincide with the services contracted by other users, so different keys are needed to encrypt the contents. These keys must be recalculated, encrypted and redistributed when a user joins or unjoins a specific group in order to prevent users who do not belong to a group from being able to access the contents. Original algorithms generate only one group key for all users, so this key must be recalculated and resent when a user joins or unjoins in the user group. This is an important problem, because a group key could be changed even when one content is performing. This paper presents a high performance implementation of one of the most employed algorithms of group key maintenance, the LKH algorithm, using reconfigurable hardware and a very high and realistic number of users (8,388,609). The performance obtained by this study improves a lot other results found in the literature in terms of both performance and number of users. [Copyright &y& Elsevier]

The Internet multicast capabilities have been used in enormous number of groups through the Internet. However, IP multicast does not deploy any mechanisms to secure the multicast messages in these groups. A lot of research efforts have been done to secure multicast messages. The idea behind the multicast security is to share a symmetric key between group members to encrypt/decrypt the multicast messages and to change this key after any membership change. The main re-keying problem is how to exchange the new group key between the group members in a scalable and secure way. In this paper we present a new multicast re-keying approach that is based on dividing the whole group into smaller subgroups. Each subgroup in turn is organized in a logical key hierarchy tree, and each subgroup member has the inverse key values of the other members in his subgroup in order to make the subgroup re-keying in a scalable and secure way. This decomposition, the proposed approach, which is named as Key Inverse Re-keying (KIR), reduces the multicast complexity from O(n) to O(log 2m) where n is the total number of the whole group members and m is the number of members in each subgroup. The performance of KIR is compared with that of other group re-keying approaches to prove its effectiveness. The comparison is undertaken according to the computational overhead, communication overhead, storage overhead, and message size. The results show that KIR enhances the group performance in terms of computational overhead and communication overhead especially at the leave operation which represents a big problem for most of the previous group re-keying protocols. [ABSTRACT FROM AUTHOR]

With the growing interest in converging fixed and mobile networks (FMC), mobile applications will require more and more resources from both the network and the mobile device. In such context, multicasting is essential because it lowers bandwidth consumption by simultaneously reaching a group of multiple recipients. Securing multicast flows has been extensively studied in the past, but none of the existing solutions were meant to handle the constraints imposed by mobile scenarios, in particular the high packet-loss rate. The need for a low overhead self-healing rekeying mechanism that is scalable, reliable and suitable for mobile environments has never been more urgent than with the arrival of FMC in 4G networks. This paper presents two self-healing recovery schemes based on the dual directional hash chains (DDHC) for the logical key hierarchy (LKH) rekeying protocol. This enables a member that has missed up to m consecutive key updates to recover the missing decryption keys without asking the group controller key server (GCKS) for retransmission. Conducted simulations show considerable improvements in the ratio of decrypted messages and in the rekey message overhead in high packet loss environments. [ABSTRACT FROM AUTHOR]

With the development of 5G and the Internet of Things (IoT), mobile terminals are widely used in various applications under multicast scenarios. However, due to the limited computation resources of mobile terminals, reducing the computation cost of members in group key distribution processes of dynamic groups has become an important issue. In this paper, we propose a computation-efficient group key distribution (CEGKD) protocol. First, an improved secret sharing scheme is proposed to construct faster encryption and decryption algorithms. Second, the tree structure of logical key hierarchy (LKH) is employed to implement a simple and effective key-numbering method. Theoretical analysis is given to prove that the proposed protocol meets forward security and backward security. In addition, the experiment results show that the computation cost of CEGKD on the member side is reduced by more than 85% compared with that of the LKH scheme. [ABSTRACT FROM AUTHOR]

Users share a group key to decrypt encryptions for the group using a group key management scheme. In this paper, we propose a re-encryption-based group key management scheme, which uses a unidirectional proxy re-encryption scheme with special properties to enable group members share the updated group key with minimum storage and computation overhead. In particular, we propose a proxy re-encryption scheme that supports direct re-encryption key derivation using intermediate re-encryption keys. Unlike multi-hop re-encryption, the proposed proxy re-encryption scheme does not involve repeated re-encryption of the message. All the computations are done on the re-encryption key level and only one re-encryption is sufficient for making the group key available to the users. The proposed scheme is the first for group key management based on proxy re-encryption that is secure against collusion. The individual users store just one individual secret key with group key derivation requiring O(logN) computation steps for a group of N users. Size of the public bulletin maintained to facilitate access to the most recent group key for off-line members is O(N) and remains constant with respect to the number of group updates. The proposed group key management scheme confronts attacks by a non-member and even a collusion attack under standard cryptographic assumptions. [ABSTRACT FROM AUTHOR]

For wireless sensor networks, key management is a challenging issue because of the limited node resources, network size, and diverse requirements, depending on the exact application. This work presents CHAT, a key management scheme based on the well-known logical key hierarchy class of protocols. CHAT exploits topological network information to reduce rekeying costs and tessellates the network into topological clusters, to further localize rekeyings, leading to greater rekeying cost reductions. A modification that adds a network key is also presented, aiming to provide a group communication scheme which still incurs a low rekeying cost. [ABSTRACT FROM AUTHOR]