Security approaches Sample Clauses

Security approaches. Railway standards do not determine requirements for security, as mentioned earlier. An exception is the standard EN 50159, which defines security requirements only for communication in transmission systems. These security requirements have been extended by further requirements after analysis. The tasks of security should be integrated into all phases of life cycle like tasks of safety. For example, EN 50159 provides a classification scheme for transmission systems. A transmission system is assigned a class according to defined criteria (Pr1, Pr2, Pr3). The standard defines threats and requirements for defences. Each classification of a transmission system has to consider concrete threats and their relation with appropriate defences. Categories and threats are described briefly below: Category 1 – Closed transmission systems, where all essential properties of the system are under the control of the safety-related system designer, and a simplified set of safety requirements can be defined; Category 2 – Open transmission systems where, although the transmission is not fully under the control of the safety-related system designer, the risk of malicious attack can be considered negligible; Category 3 – Open transmission system where there is opportunity for malicious attack, and cryptographic defence measures are required. Table 20 lists relations between threats and defences: Threats Defences Repetition X X Deletion X Insertion X Xa Xb Xb Re-sequence X X Corruption X X Delay X X Masquerade Xb Xb X a Only applicable for source identifier. Will only detect insertion from invalid source. If unique identifiers cannot be determined because of unknown users, cryptographic techniques shall be used. b Application dependent.