# Reputation-Based Trust Approaches in Named Data Networking
## 5 Discussion  
### Future Directions in NDN  
Based on the existing literature, there two distinct _use cases_ of reputation-based schemes which have been explored in the NDN architecture. **Security Attacks:** Reputation-based methods have proven to be an efficient way to mitigate attacks in NDN, based on previous work. More specifically, reputation is considered useful in order to ensure protection against cache poisoning and Interest Flooding attacks. As analyzed above, given the fact that credentials and cryptography are prohibitively expensive techniques to deploy at routers, the latter are left susceptible to cache poisoning and IFAs. Reputation-based schemes appear to be a lightweight means to cope with the aforementioned threats efficiently and thus, this seems a promising research direction. **Privacy Attacks:** Another research direction which exploits reputation in order to shield routers' caches and has been little explored, are cache snooping attacks. As cache snooping aims to the breach of consumers' privacy by inspecting the edge routers' cache content, reputation can be leveraged to detect snoopers and prevent them from violating legitimate users' privacy. Nonetheless, it is important to highlight that reputation-based schemes are neither fully explored in the above use cases, nor restricted to them. Reputation can be leveraged to assist in trust management in other research directions, where it has not been investigated yet, as well. Such potential directions are:  
**Bitrate Oscillation Attacks (BOAs):** In adaptive streaming, a client, based on measurements from the last delivered segment (e.g., assessment of the available bandwidth), decides which resolution of the next segment to request. Authors in [39; 40] propose a novel attack model implemented in dynamic adaptive multimedia streaming. In this model, an attacker requests non consecutive segments of a content, causing them to be cached in intermediate routers' Content Stores. When a legitimate user subsequently requests the same content, the already requested segments are delivered to him from intermediate caches while the rest are sent by the initial producer. In his attempt to adapt to currently measured network conditions, a client is being misled into making false estimations. As a result, the victim is forced to experience bitrate oscillations and degraded QoE. A reputation-based system can be designed in order to evaluate and detect unusual users' behaviors or to assess a priori if a content piece can be exploited by an attacker to perform a BOA. In the dynamic adaptive streaming (DAS) protocol, a user before obtaining the segments of the desired multimedia content, has to fetch a Media Presentation Description (MPD) file related to this content. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **[PERSON] et al.** & **[PERSON] et al.** & **[PERSON] et al.** & **[PERSON] et al.** & **[PERSON] et al.** \\  & [22] & [32] & [33] & [34] & [35] \\ \hline Content rating & * & * & & & \\ Network entity rating & & * & * & * & * \\ \hline Centralized & & & & & \\ Decentralized & * & * & * & * & * \\ \hline Transaction-based & * & * & * & * & * \\ Opinion-based & & & & & \\ \hline Global reputation & & & & & \\ Local reputation & * & * & * & * & * \\ \hline Rank-based & * & & * & & \\ Threshold-based & & * & & * & * \\ \hline Rule-based & * & & * & * & * \\ Incentive-based & & * & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Related work classification. The MPD file includes information regarding the characteristics of the multimedia content's segments' (e.g., available bitrates, resolutions, codecs etc). Using a reputation-based mechanism, routers could rate the content based on the information included in the received MPD files. For example, they can assign reputation values to content according to the difference between the segments' available bitrates. In this case, reputation values will express how strong potential oscillations can be.