Computer Security

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2. Computer Security

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4. Computer Security As If Your Life Depended On It Katherine Eastaughffe RESOURCEFUL RELIABLE RESPONSIBLE

5. OUTLINE • Westinghouse Rail Systems – What do we do? • Safety Critical Systems on the Railway • How do we develop Safety Critical Systems? • Where does Security fit in? • Looking to the future

6. COMPANY OVERVIEW • Company established in 1862 • Offices in Birmingham, Crawley, Croydon, Glasgow, Swanley, York, Beijing, Germany and Singapore with HQ in Chippenham • 1390 employees • Part of Invensys Rail Systems (Australia, US and Spain)

7. WHAT IS OUR BUSINESS? • Design, manufacture, installation, commissioning and maintenance of: • Railway signalling systems and equipment • Train control systems • Railway monitoring systems & control centres • Supplying Main Line and Mass Transit operators in the UK, Europe and Far East

9. LONDON’S PPP – PUBLIC PRIVATE PARTNERSHIP • Westinghouse supplying resignalling projects to Metronet consortium through Bombardier • Resignalling Victoria, District, Circle, Hammersmith, Metropolitan lines over 14 years (>1/2 of the Tube)

10. Victoria Line/SSL ResignallingStatistics • ~ $850 million contract • Resignalling of more than ½ of Tube • 150 000 people enter the system each hour • About 400 km of track • About 160 stations • Victoria line to provide > 30 trains per hour • London Underground has 2.7 million passenger journeys/day

12. AUTOMATIC TRAIN CONTROL Basic Operation Line Speed = 80 km/h Protection Profile Location Trackside Equipment

13. Train Control Systems • ERTMS (European Rail Traffic Management System) • To be deployed across Europe • DTG-R (Distance To Go- Radio) • Aimed at Metro systems • To be deployed on London Undeground

14. ERTMS • Recommended by the Uff-Cullen Inquiry for Automatic Train Protection on UK Mainline railway • Common specifications to which suppliers provide equipment • Radio Block Centre derives and sends “movement authorities” to trains via a GSM-R radio system • A movement authority specifies how far a train can travel along the route ahead • Train-borne computer calculates a safe speed based on its received movement authority

15. DTG-R • Processors send “Signalling States” from the interlocking to the train via a radio system • Train-borne computer calculates a movement authority and from that a safe speed

16. What if something interferes with the data? Basic Operation Line Speed = 80 km/h Protection Profile Location Trackside Equipment

17. What if something interferes with the data? Line Speed = 80 km/h Protection Profile Location Trackside Equipment

18. What if something interferes with the data? Line Speed = 80 km/h Protection Profile Location Trackside Equipment

19. What if something interferes with the data? Line Speed = 80 km/h Protection Profile Location Trackside Equipment

20. How do we prove our systems are safe? • Try and identify all the ways that something can go wrong • Make sure we have ways for protecting against these threats • We construct a Safety Case • One part of the Safety Case for Automatic Train Control addresses the questions: • What can go wrong with messages sent from the trackside to trains (either accidentally or deliberately) • How do protect against failures of message transmission?

21. What may go wrong with messages? • Repetition of Messages • Deletion of Messages • Insertion of Messages • Resequencing of Messages • Corruption of Messages • Delay of Messages • Masquerade of Messages

22. Repetition of Messages • Due to failure of equipment eg message buffer is not properly flushed • Due to deliberate storage and replay of messages • Sequence Numbers and Timestamps

23. Sequence Numbers • Add a running number to each message exchanged between a transmitter and a receiver • Receiver checks that number is within suitable range of number of previous message • Suitable range means: • Eg between 1 and 30 greater than previous number (module 255) for an 8 bit number • Suitable range depends on the expected frequency of transmission. • This ensure message in specified range is no older than x seconds/minutes • Except that if the message is really old, then it might be in range, because sequence numbers have gone right the way round!!

24. Timestamps • Timestamps can plug the hole that sequence numbering technique has • Transmitter adds a timestamp to message • Receiver checks that timestamp is within given tolerance of the timestamp of previous message • Bandwidth may prevent timestamp being sent with all messages • Need to be careful about the 1st message received from a transmitter – how do you know its clock is right and the message is not years old.

25. Deletion of Messages • May be the result of equipment failure • Or Denial of Service attack • Most likely source of disruption of message transmission • Design the system to be “fail-safe” – if messages are not received it will not cause a hazard • Timeout on receipt of messages. If a train does not receive any messages after a given period of time, braking will be applied • In emergency situations, you may want to know that a message has been received, in which case there must be an acknowledgement

26. Insertion of Messages • Due to cross-talk • Due to deliberate insertion of messages • Sequence numbers will protect against a large number of false messages because the sequence number is unlikely to be within the expected range • Otherwise see masquerading of messages

27. Resequencing of Messages • Messages received in different order to that transmitted • Sequence Numbers and Timestamps

28. Corruption of Messages • Accidental changes eg from Electromagnetic Interference or collision of messages • Deliberate changes • Safety Codes • CRC (Cyclic Redundancy Codes) • Hash Codes • Cryptographic Block Codes (Message Authentication Code)

29. ERTMS – Encryption • Uses a MAC – a function of the whole message and a secret key • A private key for each train • Block Cipher used is single DES with modified MAC algorithm 3

30. Delay of Messages • Timestamps • Timeouts – if you don’t receive a message within a given period, enter a fail-safe state, that is, shut-down and apply braking

31. Masquerading of Messages • Use of identifiers • Use of cryptographic techniques

32. Security of Rail Networks • Of course, there are easier ways of deliberately disrupting railways than spoofing/deleting messages from trackside to train • Difficult to gain physical access to network

33. An Interesting Website • www.atcsmon.com • Allows you to graphically monitor train traffic on railroads that use the Association of American Railroad’s Advanced Train Control System (ATCS) Specification 200 protocol (among others) • All you need is a radio scanner! That is when you’re not listening to the police, or baby monitors

34. Some other Security Issues • Security of map data and software loaded into train control units • Management of private keys for each train • The future will involve satellite positioning systems (Galileo) and use of more and more COTS products, which increase the security risk

35. Summary • Security issues can be safety issues too • To get approval for systems, you have to show that you have considered threats from message integrity and protected against them • Real applications for cryptographic techniques

36. Further Information • www.westinghouserail.co.uk • Railway Safety Standards • BS EN 50159: Railway Applications – Communication, Signalling and Processing Systems • ERTMS Standards - www.aeif.org/ccm/doclist.asp • Lots of information about Communications Systems for train control, US focussed, no future maintenance, www.tsd.org • “Safeware: System Safety and Computers” by Nancy Leveson. Addison Wesley 1995 • IEE Website (Institute of Electrical Engineers) – www.iee.org • Railway Professional Network • Functional Safety Professional Network

37. WESTINGHOUSE RAIL SYSTEMS RESOURCEFUL RELIABLE RESPONSIBLE