# SPD-Safe: Secure Administration of Railway Intelligent Transportation Systems
## 4 Network Layer Security  
The protection of the network link is essential in order to safeguard the underlying systems of critical railway infrastructure (e.g., WSN, signaling equipment, surveillance, etc.). For this purpose, as mentioned, SecRoute [61] is developed; a novel defence primitive that provides the core security properties for authentication, integrity, and confidentiality, along with energy-aware secure routing and authorization.  
The secure routing protocol protects the involved entities from malicious operations while improving performance and offering load-balancing. It consists of three main primitives:  
* The cryptographic service with the Timed Efficient Stream Less Tolerant Authentication protocol ( TESLA) [60], which implements message authentication, confidentiality, and integrity;
* The efficient secure routing service with the Self-Channel Observation Trust and Reputation System (SCOTRES) [62] that safeguards the communication link against ad-hoc routing attacks and network layer vulnerabilities:
* The authorization service with the Policy-Based Access Control framework (PBAC) [42], which offers authorization and access control based on policies.  
Table 2 summarizes the overall security properties that are provided by the integrated network layer defense mechanism and the relevant threats and attacks that are countered, while a brief analysis is presented in the subsections that follow. More details regarding the three services are presented in the relevant papers for TELSA [60], SCOTRES [62], and PBAC [42], respectively.  
Figure 2 presents the block diagram of the main SPD-Safe modules and their connection.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Primitive** & **System Property** & **Countered Threats** \\ \hline \multirow{4}{*}{TESLA} & Authentication & Impersonation, Sybil attacks \\ \cline{2-5}  & Integrity & Data tampering, \\ \cline{2-5}  & Forward security & Replay attacks \\ \cline{2-5}  & Confidentiality (optional) & Disclosure \\ \hline \hline \end{tabular}
\end{table}
Table 2: Protection aspects of the SPD-Safe’s network layer security.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Primitive** & **System Property** & **Countered Threats** \\ \hline Topology-awareness & Attacks on \\ \hline Energy-awareness \& Load-balancing & Energy dissipation, \\ \hline Channel health & Jamming attacks \\ \hline \multirow{5}{*}{SCOTRES} & \multirow{5}{*}{Reputation} & Malicious or selfish activity on \\  & & the network operations of: \\  & & Routing (link spoofing, \\  & & routing table poisoning, \\  & & HELLO flooding, false \\  & & link break, loops, \\  & & nonexistent paths), \\ \cline{1-1}  & & Forwarding (blackhole, \\  & & grayhole, sleep \\  & & deprivation), \\ \cline{1-1}  & & Or making \\  & & recommendations \\  & & (badmouth, \\  & & ballot-stuffing) \\ \hline \multirow{5}{*}{PBC} & \multirow{5}{*}{Authorization based on policies} & Overall misbehavior on the \\  & & previously mentioned \\ \cline{1-1}  & & networking perspectives \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 2: The building blocks of the SPD-Safe framework.