# Reputation-Based Trust Approaches in Named Data Networking
## 3 Reputation-Based Approaches in NDN
### Reputation-Based Systems
Authors argue that the further a router is from an attacker, the more poisoned copies are received for a specific content piece because of multi-path propagation. Based on this assumption, they use the number of received poisoned copies of a certain content as a means to decide how much to decrease the reputation of routers that forward fake content. Reputation values are updated based on negative verification results generated by consumers and forwarded back to the routers following the reverse transmission path. This is similar to Reference [32], although the reputation value of a malicious router is significantly decreased when the router is punished, it takes time for it to recover. The computed reputation value of a router represents how trusted this router can be and determines how likely it is for this router to be included in the transmission path. In other words, routers choose their well-reputed neighbors as next hops to forward Interests and thus, malicious routers are temporarily excluded from the transmission path. ROM's efficiency is evaluated by comparing it with the Interest-Key Binding (IKB) rule [23], which states that an interest must reflect the public key of the producer. More specifically, IKB exploits an Interest field called PublisherPublicKeyDigest (PPKD). PPKD contains the SHA-256 (Secure Hash Algorithm-256)digest of the publisher public key. According to this method, the public key of every received content is being hashed by routers and compared to the PPKD of their related PIT entry. The content object is forwarded and cached by routers and its signature is verified by consumers if and only if the hash and the PPKD match. Otherwise, it is discarded. However, since this approach is credential-based, it comes with its flaws. A consumer that issues an Interest has to fetch the PPKD of the desired content's provider in advance. In addition, the PPKD has to be verified at every hop. As these features increase the delay and reduce the network throughput, ROM outweighs IKB. In particular, evaluation results provided in [33] indicate that ROM improves network latency by 85.5% and throughput by 84%. Regarding cache snooping, Reference [34] proposes a reputation-based method to detect adversaries. As explained in Reference [34], a snooper not only requests but even excludes content so that he can have a full picture of the cached content. Based on this assumption, the authors consider a user malicious when high interest and exclusion rates are measured in a short time period, as well as a high cache hit rate from the local cache at the same time. These features are used in the calculation of a user's reputation and subsequently, in the evaluation of another metric, the user's trust value. The trust value is compared against a threshold in order to detect snoopers. Besides cache-related attacks, reputation-based schemes are used as a means to mitigate Interest Flooding attacks. ICRP (An Interest flow control method based on user reputation and content name prefixes ) [35] assigns a reputation value to each consumer which represents the transmission degree of Interests requiring existing content objects. Aiming at preventing on-off attacks, while calculating reputation values, ICRP weighs both the past and the current behavior of users. Computed reputation values are compared against a predefined threshold, and if a user's reputation is below this threshold, he/she is considered malicious. Upon the detection of a malicious consumer, its Interests are accepted according to its reputation value. The lower the reputation value, the higher the Interest drop rate. Moreover, ICRP observes and counts the Interests sent by detected attackers and creates a blacklist which includes non-existent name prefixes. Therefore, ICRP identifies the malicious users based on reputation values of consumers, while it detects and records non-existent content names and thus, limits the flow of malevolent Interests in the network.