# Decentralized Documentation of Maritime Traffic Incidents to Support Conflict Resolution
## 5 Application and Evaluation
### Discussion  
The functionality of the approach for a decentralized documentation of critical traffic situations was demonstrated based on a realistic evaluation scenario within a maritime SmartKai testbed. Furthermore, the presented approach fulfills the requirements of Section 2.4:  
1. Firstly, if a participant wishes to document its data recording, it must be sent to the identified TSA in hashed form. This makes the documentation process completely independent of the format and content of the underlying data. The only prerequisite is that it must be possible to hash the documented data. This is no issue for any data stored in files, and even streamed data can be hashed by breaking it down into individual packets. 2. Secondly, as proof that the data has not been manipulated after recording, a hash of the data is sent to a TSA approved by all participants. This TSA provides the hash with a timestamp and signs it with its digital signature. In this way, it can be cryptographically verified at any time whether the data has been manipulated after it has been recorded. 3. The presented approach puts a strong focus on protecting the sovereignty of individual data providers. Each participant is able to record and persist his data independently. As long as there is no conflict, the data is also not shared with the other participants. Even in the event of a conflict, the data provider has the option not to share the data. Additionally, only a hash of the original data is transmitted to the TSA itself, so even the TSA cannot draw any conclusions about the actual data. 4. Furthermore, anyone can join the P2P network used for communication as long as the participant knows the IPs of the other participants. The best way to distribute the IPs among the participants depends on the use case for which the documentation has to be created. 5. Lastly, if not all participants are equipped with the system for documentation, it is still possible for the remaining participants to document a situation among themselves in a tamper-proof manner. If no participant is equipped with the system or it is not \begin{table}
\begin{tabular}{c c c} \hline \hline
**Phase** & **Duration in SmartKai Testbed** & **Average Duration in Simulation** \\ \hline Establishing communication channel & 636 ms & 30 ms \\ Derive a common trusted set of TSAs & 313 ms & 100 ms \\ Signing and storing of a data chunk & 118 ms & 106 ms \\ Total & 1067 ms & 236 ms \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Time required by the approach in the evaluation scenario depending on the respective phase. possible to reach an agreement during TSA negotiation, the fallback TSA mechanism takes effect (c.f. Section 4.2). In this case, the participant documents his data with a TSA selected by himself in order to establish at least a basic trust in the documentation. In order for the approach to be used for documenting critical traffic situations, it is important that the entire process from establishing contact to documenting remains within a reasonable time frame. Unlike in other domains such as the automotive domain, critical traffic events in the maritime domain can often be determined several minutes in advance, so the required time of 1068 ms should not have a negative impact in most cases. In addition, the developed approach was also compared with similar existing approaches to discuss the strengths and weaknesses of each approach (cf. Table 3). We compared the existing methods to reconstruct traffic events, such as VDR and logbook, the blockchain-based approach and the TSA-based approach presented in this paper. The evaluation criteria include the possibility of documenting any data (Variety of data), the tamper-proofness of the documentation (Tamper-proof), the local persistence of the data (Data Sovereighty), the complexity of the overall system and the readout process (Complexity), and the dependence on an Internet connection (Connectivity).