Information Security of Embedded Systems : Embedded Systems Design Prof. Dr. Holger Schlingloff Institut für Informatik und Fraunhofer FIRST

Embedded Security © Prof. Dr. H. Schlingloff Structure 1. Introductory example 2. Embedded systems engineering 1.definitions and terms 2.design principles 3. Foundations of security 1.threats, attacks, measures 2.construction of safe systems 4. Design of secure systems 1.design challenges 2.safety modelling and assessment 3.cryptographic algorithms 5. Communication of embedded systems 1.remote access 2.sensor networks 6. Algorithms and measures 1.digital signatures 2.key management 3.authentification 4.authorization 7. Formal methods for security 1.protocol verification 2.logics and proof methods

Embedded Security © Prof. Dr. H. Schlingloff Embedded Systems Design Waterfall or V-Model small to medium design groups civil engineers, electrical engineers software often not valued Model-based design Matlab/Simulink, UML code generation Product lines no real system is developed from scratch look-and-feel, component reuse

Embedded Security © Prof. Dr. H. Schlingloff The State of an Object Technical systems convert or relocate physical objects (matter and/or energy) Physical objects are characterized by their state State = observable appearance of an object in space and time a complete description of a system in terms of parameters such as positions and momentums at a particular moment in time (wiki) shape, size, position, movement, temperature, pressure, voltage, … Observation of physical state by sensors camera, folding rule, light sensor, tachometer, thermometer, … Modification of physical state by actuators motor, valve, relais, transducer, heater, …

Embedded Security © Prof. Dr. H. Schlingloff Technical Systems and Processes Technical system: perform technical process Technical process: reshaping or transporting physical objects Description of states by state variables formally, a state is a mapping of variables to values Description of processes by state changes discrete state changes are called events continuously changing state constituents are sometimes called signals

Embedded Security © Prof. Dr. H. Schlingloff Example A toaster what is the technical process? what are the states, events and signals of the (technical) process? what are the boundaries of the system? which information processing is to be done? what are the interfaces between technical system and information processing component?

Embedded Security © Prof. Dr. H. Schlingloff Systematic design of embedded systems 1. Identify the boundaries of the system, the technical process, the control task focus on user perspective 2. Identify the state constituents of the system physical properties: mass, pressure, temperature, … user interfaces: switches, displays, interactions, … 3. Formally represent states by state variables in general, state variables are time-dependent functions; a state of the system is given by the value of all state variables at a given moment each state variable has a dimension and range of values (e.g. temperature t in °C or °F, length l in m, mm or in)

Embedded Security © Prof. Dr. H. Schlingloff Describe properties of the variables side conditions, e.g. 0<t<100 (physical) relations between variables, e.g. t Toast <t Heater 5. Determine which variables can be monitored and which can be controlled monitored variable: can be observed by the controller controlled variable: can be influenced by controller some environment variables are both monitored and observed 6. Define control functionality mapping of monitored into controlled values, e.g. h=c*|t s -t i |

Embedded Security © Prof. Dr. H. Schlingloff Controlling Technical Processes Control theory design, identification and analysis of systems to make them perform specific tasks or make them behave in a desired way (free dictionary) DIN Steuerung (open loop control) ist ein Vorgang in einem System, bei dem eine oder mehrere Größen als Eingangsgrößen die Ausgangsgrößen auf Grund der dem System eigentümlichen Gesetzmäßigkeiten beeinflussen. Regelung (closed loop control) ist ein Vorgang, bei dem fortlaufend eine Größe, die Regelgröße (zu regelnde Größe), erfasst, mit einer anderen Größe, der Führungsgröße, verglichen und im Sinne einer Angleichung an die Führungsgröße beeinflusst wird. Achtung: Steuergeräte sind meist zur Regelung von Prozessen!

Embedded Security © Prof. Dr. H. Schlingloff Controls Open-loop control (Steuerung) Example: Toaster without thermostat Closed-loop control (Regelung) Example: Toaster with thermostat Controls Plant (Strecke) Reference value (Sollwert) Controls output / System input (Stellgröße) System output (Regelgröße) Regler Regelstrecke Reference (Sollwert) System input (Stellgröße) System output (Regelgröße) Stellglied (Aktuator) Messglied (Sensor) Control signal (Reglersignal) Measured value (Istwert) Environment (Störgröße) (Führungs- größe) (Rückführungsgröße)

Embedded Security © Prof. Dr. H. Schlingloff Other pictures for the same Controller (Steuer- gerät) Aktuators Sensors Plant (Strecke) Environment techn. system Controller

Embedded Security © Prof. Dr. H. Schlingloff PID-Controller proportional–integral–derivative controller proportional part: reaction to the current deviation - e.g. out(t) = 5 * |in(t) – refval| integral part: reaction based on the accumulated recent deviation - e.g. out(t) = 0.3 * Σ t =0 (in( ) – refval) derivative part: reaction based on the rate at which the deviation has been changing - e.g. out (t) = 0.1 * d/d (in( ) – refval( )) Tuning (setting parameters) can be manually or by tools (e.g.

Embedded Security © Prof. Dr. H. Schlingloff

Embedded Security © Prof. Dr. H. Schlingloff Controller variables Discretization: monitored and controlled variables are translated by A/D and D/A converters into input and output variables of the control software attention: a controller output is a plant input and vice versa! Usually, the controller has additional internal variables hidden to the outside! Testing interfaces are security holes!

Embedded Security © Prof. Dr. H. Schlingloff Sense-Think-Act Functional systems follow the paradigm input-process-output Embedded systems follow loop{sense-think-act} main loop repeated indefinitely: - read sensor values - calculate deviation or action - write actuator outputs