Related Works. The number of nodes in a fully secure network can be increased by using multiple key spaces. In [14], ω key spaces are generated and each node is given a sub-set of τ randomly chosen keys from ω. After deployment, nodes discover their common keys and use the Xxxx’x scheme to form pairwise keys. The scheme uses a similar idea to the probabilistic scheme of Eschenaeur-Gligor [3] where nodes are given a random set of keys from a global key space. In these schemes the aim is to achieve full connectivity, but not necessarily complete connectivity like a full mesh. Another approach also uses Xxxx’x scheme with multiple key spaces to improve resistance to the Xxxxx attack [15]. In [16], the scheme for a clustered topology is proposed. Here, the cluster-heads implement the Xxxx’x scheme to derive pairwise keys among themselves. Non cluster-head nodes do not implement the Xxxx’x scheme. Instead, they store a pre-computed secret key Ki for use with a clus- ter head. Prior to deployment, the base station computes the pairwise keys of this node with a certain number of associated cluster-heads. These are then combined into a secret key Ki and stored in the node, together with the identities (IDs) of the associated cluster-heads. When a node needs to establish a secure link with a physical cluster-head, − it sends its own ID and the IDs of its associated cluster- heads. The physical cluster-head forwards the node’s ID to the associated cluster-heads to compute the pairwise keys using Xxxx’x scheme and thereby derives the secret key Ki. In this way, non-cluster head nodes store minimum keying material and do not need to perform any key computation computation. Instead, these are delegated to the cluster heads which carry the additional load of communicating with other cluster heads to derive the key with a non cluster-head node. The network size would still be limited to the (m 1) nodes for a fully secure network. Since cluster-heads establish pairwise keys among themselves using the basic Xxxx’x scheme, the key size and memory requirements, and network size would still be limited to the original scheme.
Related Works. 11.1 Should the Subcontractor’s performance depend in any way on the proper performance of another person, for example, a consultant or another contractor, the Subcontractor must take all reasonable steps to enquire into and discover any defects in such performance and the Subcontractor must promptly provide a written report to Savcor ART relating to any defects it discovers.
Related Works. In [8] we have presented a multicoordinated consen- sus protocol (MCC) that extends Fast Paxos [26], with its fast and classic modes. The protocol can switch be- tween classic, fast, and multicoordinated modes in run- time. This feature allows the protocol to be deployed in many different environments and to adapt to changes therein during the execution. It is also an important tool in the study of agreement protocols, by using the right combination of round types and recovery technique, our protocol emulates most consensus protocols that we are aware of. In [9] we have shown the use of the multicoordi- nated mode in solving generic broadcast and discussed its relation to generalized consensus. We reviewed the mul- ticoordinated execution mode in Section 2.5 and MCC in Section 3. In this paper we tackled the problem of efficiently reaching agreement in a network organized as groups of agents. Our solution is an extension of the Collision- Fast Paxos protocol [37], which does not consider groups. For the reader’s convenience we explained CFPaxos in Section 4.2. The same problem, agreement in groups of agents, was studied by Xxxx and Xxxxxx [21]. Their hi- erarchical consensus algorithm recursively agrees on pro- posals over a multilevel tree of agents. More specifically, in their protocol each set of agents in a given level of the same branch of the tree constitute a group. From the leaves to the root, agents in the same group agree on a value to be their proposal on the upper level, until they have agreed on a single value at the root of the tree. The cost of such an approach depends on the choice of consensus algorithm used inside each group. There are two main differences between Xxxx and Xxxxxx’x work and ours. First, our protocol is better suited for applica- tions that need to agree on all proposals, not just a sin- gle one. This is is the case, for example, when solving atomic broadcast; solutions based on consensus require each command proposed but not decided to be proposed again in a new consensus instance. Because our protocols solve M-Consensus instead, all proposals may be part of a single decision. Second, in Kooh and Xxxxxx’x protocol, agents are replicated using consensus: an instance is used to agree on each state change. In our approach, we let the coor- dinators in each quorum diverge and only use consensus to recover from failures. The price we pay is in terms of messages sent from the group—since each coordina- tor may be in a different...
Related Works. This paper offers an approach to technically con- verge the quality-related ontologies of service, expe- rience, and business as introduced in (Xxx Xxxxxxx, 2001; Xxxxxx and Xxxxxxx-Xxxxxx, 2006). Most other authors address technical perspectives on SLA in SOA. From the IT architecture point of view, authors deal with SLA descriptions of performance modelling (Xxxxxxx, 2008), SLA-driven development (Xxxxxxxxx et al., 2009) or dependability through- out the life cycle (Xxxxxxxxx and Xxxxx, 2010). In operations management SLA are mostly enforced through an distribute-and-enforce tactic. By (Xxx et al., 2008; Xxxxxxxx and Xxxxxxxxxx, 2008; Xxxx et al., 2009; Xxxxxxxxx and Xxxxxxxx, 2008) highly detailed SLAs are defined, distributed and then en- forced on each member of a service cascade. The complexity to manage such approaches increases with the complexity of the given cascade. (Xxxxxxxxx and Xxxxxxxxxx, 2008) decouples SLA operations man- agement from the complexity of a service cascade. This paper presents a similar approach and advances it by embedding BSLA in a whole life cycle concept (Xxxxxxxx and Xxxxxxx, 2010). Technical operations is focused on the technical monitoring of technical re- source thresholds. Three types can be distinguished: active, passive and agent-based (Xxxxx and Xxxxxxxx, 2010). Other authors propose the workflow monitor- ing of business process workloads. It is focused on the workflow state rather than underlying technical mea- surements (Ou et al., 2008). In contrast, (Xxxxx et al., 2008) aims to provide a non-intrusive workflow mon- Xxxxxxxx B., X. Xxxxxxx A., X. Xxxxx R. and Xxxxxxx X.. AGREEING ON AND CONTROLLING SERVICE LEVELS IN SERVICE-ORIENTED ARCHITECTURES. DOI: 10.5220/0003871702670270 In Proceedings of the 2nd International Conference on Cloud Computing and Services Science (CLOSER-2012), pages 267-270 ISBN: 978-989-8565-05-1 Copyright Ⓧc 2012 SCITEPRESS (Science and Technology Publications, Lda.) 267 CLOSER 2012 - 2nd International Conference on Cloud Computing and Services Science itoring approach combined with active SLA manage- ment. This paper broadens this approach to incorpo- rate technical monitoring data and address general IT services based on IP networks.
Related Works. Since the presence of foundational Xxxxxx-Xxxxxxx (DH) protocol [12], several other protocols have been proposed for the group case. The original idea of extending the 2-party DH scheme to the multi-party setting dates back to the classical paper of Ingemarsson [16]. Following their work, Xxxxxxx et al. [22, 23, 24] proposed a family of protocols known as Group Xxxxxx- Xxxxxxx (GDH.1, GDH.2, GDH.3). In these protocols, the last group member serves as a controller and performs most of the computation, therefore, it needs more energy compared with other group members. Owning to the limitation of the nodes energy, the GDH protocol family is not suitable for the Ad-hoc networks. Perrig [21] proposed a tree-based key agreement scheme. After that, Xxx et al. [18] extended the work of [21] to design a Tree-Based Group Xxxxxx- Xxxxxxx (TGDH) protocol. Compared with GDH protocols, it scales down the number of exponentiations and received messages required by the last group member to avoid excessive computational and communication costs required by one node. But TGDH protocol still requires each group member to perform large modular exponentiations and transmit/receive long messages. So the TGDH protocol is also inadequate for Ad-hoc networks. After the work in [4, 9, 25] many other scholars have done abundant related research. However, fairly few research deals with provably-secure group key agreement in a concrete and realistic setting. It is only recently that [20], has presented the first group key agreement scheme proven secure in a well-defined security model. Ng et al. [20] incorporated the identity based cryptosystem with bilinear map and broadcast encryption scheme to construct a secure communication scheme for MANETs. In their scheme, the group members do not perform any message exchanges during the generation process of a group key. However, its security relies on the random oracles. It has been shown that when the random oracles are instantiated with concrete hash functions, the resulting scheme may not be secure [3, 10]. Then, Zhang et al. [26] designed a new scheme which is proved secure in the standard model rather than the random oracles model. Unfortunately, those schemes suffer from long ciphertexts, i.e., the secret message broadcasted to the users will grow linearly with the number of receivers. With the increment of network scale, the shortcoming mentioned above will lead to even serious problems.
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Related Works. Recently a number of protocols have been proposed to solve the problem of key management over wireless ad hoc networks. Key pre-distribution has been discussed in several approaches. Xxx, Xx, Xxxxx, and Xxxxxxx (2003) discuss a secure communication between two nodes in an ad hoc networks using probabilistic key sharing scheme in which enables two nodes to establish a pairwise shared key. The protocol used the off-line key server in key pre-distribution phase what is used to initialize all the nodes. Their protocol is based on two techniques including probabilistic key sharing and threshold secret sharing. A password based multi-party key agreement scheme was proposed Xxxxxx and Ginzboorg (1999) where all the nodes are assumed to share a password. Basagni, Herrin, Rosti, and Xxxxxxx (2001) described a secure ad hoc network in which all the nodes share a group identification key stored in tamper-resistant devices. Though all the above schemes perform efficiently, they require that all the nodes have some pre-determined knowledge. In ad hoc networks where mobile nodes do not grant the privilege of knowing other group members beforehand, assumption of such a pre-shared secret is invalid. The concept of mobile certificate authorities has been discussed by Xx and Xxxxxxxx (2002) and Kong, Xxxxxx, Xxx, Xx, and Xxxxx (2001). In such schemes, the responsibilities of a CA are distributed among a set of wireless nodes. A subset (threshold) of such CAs must be contacted to obtain a valid certificate. Such schemes have several advantages such as providing data integrity, authentication and non- repudiation. The drawbacks of such schemes are: (a) identifying nodes that perform the role of the CAs, consequently these nodes must spend more power; (b) constant availability of a threshold of CAs in a mobile network; and (c) the use of the computationally expensive public key encryption systems. Public key certificates are also used by Hubaux, Buttyan, and Capkun (2001), where all the nodes are assumed to maintain a local certificate repository and a probabilistic method is used to achieve a certificate chain between two nodes. This scheme requires that all nodes are preloaded with a set of certificates and it is possible that two nodes in the ad hoc network do not achieve a certificate chain. Also, the authors in (Xx et al., 2002; Xxxx et al., 2001; Xxxxxx et al., 2001) did not address the distinct features of secure group communication such as group key formation and membe...
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Related Works. In this section, we give a short review of SLA schemes and briefly explore the state of the art including SLA for communication network and energy aware SLA for cloud environment.
