*2.9.8. SAR - Security-aware routing*

250 Wireless Sensor Networks – Technology and Protocols

function.

a complete reputation mechanism that defines three different types of reputation: (i) Subjective Reputation - reputation observed locally by a node with regards to other nodes (direct observations), (ii) Indirect Reputation - reputation provided by nodes to other nodes which includes only the positive reports by others and (iii) Functional Reputation - also referred as task-specific behavior, which are weighted according to a combined reputation value that is used to make decisions about cooperation or gradual isolation of a node. That is, Subjective Reputation and Indirect Reputation are merged by means of a weighted combining formula in order to compute a final value of reputation concerning a specific evaluation criterion (e.g. packet forwarding) forming Functional Reputation, the last type of reputation considered. By combining different functional reputation values concerning different evaluation criteria, a global reputation value may be estimated. The subjective reputation is computed by giving more relevance to past observations than to recent ones. Subjective Reputation values are updated on the basis of a Watchdog mechanism, if misbehaviour is identified. Indirect Reputation values are updated by means of a reply message that contains a list of all entries that correctly behaved in the context of each

In this work, distribution of positive ratings is allowed so as to avoid potential denial of service attacks. In case reputation of an entity is negative, the execution of any requested operation will be denied by all other entities in the system. The system assumes a DSR routing in which nodes can be requesters or providers. The rating is done by comparing the expected result with the actually obtained result of a request. Here, nodes exchange only positive reputation information. The authors argue that this prevents a false-negative (badmouthing) attack, but do not address the issue of collusion to create false praise. In CORE, members have to contribute on a continuing basis (thereby enforcing node cooperation) to remain trusted or they will find their reputation deteriorating until they are

*2.9.7. SORI - Secure and objective reputation-based incentive scheme for ad hoc networks* 

SORI Scheme for Ad Hoc Networks) [4] targets only the non forwarding attack. SORI monitors the number of forwarded packets from neighborhood and the number of forwarded packets to neighborhood. Reputation rating is then acquired by computing the ratio between the two numbers with a consideration for the confidence in the rating proportional to the number of packets that are initially requested for forwarding. Second hand information is delivered only to the immediate neighbors. This rating source; however, is weighted by what is called credibility, which is derived from the rating ratio. The delivery of the second hand information is achieved by hash-chain based authentication. SORI consists of three components, namely, neighbour monitoring (used to collect information about packet forwarding behaviour of neighbours), reputation propagation (employed so as to share information of other nodes with neighbours) and punishment (involved in the decision process of dropping packet action, taking into account the overall evaluation record of a node and a threshold so as to consider collision events). Reputation rating formation considers first-hand information weighted by a confidence value used to describe how

excluded. CORE does not provide for a second-chance mechanism.

SAR [70] (Security-Aware Routing) is a protocol derived from AODV and based on authentication and a metric called the hierarchical trust value metric. The hierarchal trust values metric governs routing protocol behavior. This metric is embedded into control packets to reflect the minimum trust value required by the sender. Thus, a node that receives any packet can neither process it nor forward it unless it provides the required trust level presented in the packet. Moreover, this metric is also used as a criterion to select routes when many routes satisfying the required trust value are available.
