Wireless Network Security Spring 2015

Transcription

1 Wireless Network Security Spring 2015 Patrick Tague Class #4 OMNET++ Intro; Physical Layer Threats 2015 Patrick Tague 1

2 Class #4 OMNET++ Intro PHY layer basics and threats 2015 Patrick Tague 2

3 Intro to OMNET++/INET 2015 Patrick Tague 3

4 What is OMNeT++? It's a discrete event simulator that provides a base for network simulation Communication networks Queuing networks Digital logic networks ' ' networks Two components Event-driven simulation kernel Utility classes Implementations of common functionality for network simulations Math functions Statistics Physical network characteristics helper classes 2015 Patrick Tague 4

5 Simulation Kernel Simulation kernel terminates when: No more events in event queue Termination condition reached User terminates 2015 Patrick Tague 5

6 Simulation Models A simulation model consists of modules, which are grouped/connected together. Modules that are grouped together are themselves modules Provides a module hierarchy In OMNeT++, a simulation model is also called a network A network (simulation model) is itself a module 2015 Patrick Tague 6

7 Module Types What goes into a simulation model? It all starts with Simple Modules Base building blocks Declared using the NED language Backed by C++ classes which define their behavior Defines parameters to pass to (C++) implementation Simple modules group together to form Compound Modules Declared using the NED language Defines parameters to pass to simple modules 2015 Patrick Tague 7

8 Simulation Models - Gates Gates allow for message passing Messages pass between gates using connections Two gates can be directly linked via connection Think wired communication network Connections can also be used to directly pass a message to an unlinked gate Think wireless communication network Connections can be defined and reused Called channels 2015 Patrick Tague 8

9 Simulation Models Patrick Tague 9

10 INET Communication networks simulation package for OMNeT++ Provides models for many wired/wireless networking protocols These models build upon each other to create simulation models of communication nodes, and networks Gives OMNeT++ communication networks support without us having to write our own protocols Easy to install comes bundled with OMNET++ There's a new dev version available 2015 Patrick Tague 10

11 Output vectors Statistics Collection Time-series data Stuff that gets recorded during a simulation Output scalars Aggregate stuff recorded at the end of a simulation Mean of something, std dev of something, 2015 Patrick Tague 11

12 Declaring Statistics In NED: Statistics stat_name = variable emitted from the C++ class properties = what to record, and in which form (scalar, received_pkt is a variable emitted each time a packet is received We are recording to a scalar the total packets received We are recording to a vector each time a packet is received Note the '?' - this means its optional 2015 Patrick Tague 12

13 Statistics Collection Emitting variables (signals) ec193 Register the signal by name registersignal( stat_name ) stat_name must match that given in the NED declaration Function returns an id for the signal Emit the signal when appropriate emit(signal_id, value) signal_id = id of signal (mapped to stat_name)» simsignal_t signal_id = registersignal("stat_name") 2015 Patrick Tague 13

14 Example Time inet/examples/wireless/hosttohost/ 2015 Patrick Tague 14

15 PHY 2015 Patrick Tague 15

16 Wireless PHY The wireless PHY is responsible for delivering a bit stream from a transmitter to one or more receivers. It's not as easy as it sounds. Tx/Rxs need to be coordinated in time, space, frequency, phase, encoding/language Wireless means there are many sources of error, reasons for failure, etc Patrick Tague 16

17 PHY Standards In WiFi networks, IEEE defines several versions of the PHY, including extensions for mesh, vehicular, etc. In telecom, the GSM 05.xx series defines the Um physical layer, and other standards build on it, including ITU-T standards like 4G. In PANs, standards like (Bluetooth),.3 (high-rate, e.g., UWB), and.4 (low-rate, e.g., Zigbee) all define their own PHY models Patrick Tague 17

18 Wireless PHY Services Various parts of PHY operation: Radio interface: spectrum allocation, signal strength, bandwidth, carrier sensing, phase sync, Signal processing: equalization, filtering, training, pulse shaping, signaling, Coding: channel coding, bit interleaving, fwd error correction, Modulation (mapping bits to signals) Topology, antennas, duplex/simplex, multiplexing, and so much more PHY is typically the most complex part of a wireless network 2015 Patrick Tague 18

19 What are the basic threats faced at the PHY layer? 2015 Patrick Tague 19

20 Back to the Party 2015 Patrick Tague 20

21 Physical Layer Misbehavior Open, shared medium is vulnerable Anyone can talk greedy or malicious nodes can easily interfere Prevention/degradation of communication via jamming Cutting off available resources influences network control, operation, and performance Anyone can listen curious or malicious nodes can easily eavesdrop on communication Recovery of information exchanged by neighbors (violation of data, identity, operation/intention privacy) Inference/learning, tracking, observing 2015 Patrick Tague 21

22 Challenges How can we prevent a curious or malicious party from eavesdropping on wireless transmissions at the physical layer? How can we prevent a greedy or malicious party from interfering with PHY transmission and reception? For both: Short answer, we can't Long answer, we can make it much more difficult 2015 Patrick Tague 22

23 Spread Spectrum Spread spectrum is an extension of multiplexing that uses randomization to increase diversity and improve performance in various ways Frequency-hopping spread spectrum (FHSS) builds on FDM allowing devices to pseudo-randomly move among frequency channels If one channel is particular good or bad, everyone shares it randomly Direct-sequence spread spectrum (DSSS) builds on CDM allowing devices to pseudo-randomly move among different code spaces Code spaces are analogous to frequency bands 2015 Patrick Tague 23

24 Multiplexing FDM frequency division multiplexing CDM code division multiplexing TDM time division multiplexing (flip x-y) TDM + FDM as in GSM images from [Erik Lawrey; SkyDSP.com] 2015 Patrick Tague 24

25 FHSS FHSS: Sender and receiver synchronize a hopping pattern over a large bandwidth 2015 Patrick Tague 25

26 DSSS encoding maps long symbols to sequences of short chips DSSS Encoding Shorter chip duration means wider bandwidth 2015 Patrick Tague 26

27 FHSS: Benefits Narrow-band interference only has an effect for a small fraction of the time Single-channel eavesdroppers can't follow the signal, need to use much wider bandwidth to hear everything DSSS: Narrow-band interference is despread at the receiver, more like quiet wide-band noise Other signals are (nearly) orthogonal Eavesdropper has to know/guess code to decode 2015 Patrick Tague 27

28 Cryptographic SS Building off basic spread spectrum, we can add cryptographic randomization to make hopping schedule and code sequences secret Using a symmetric key as a seed to a PRNG makes the hopping schedule or code sequence secret In both cases, this requires symmetric key management, which has its own issues 2015 Patrick Tague 28

29 Issues with Spread Spectrum To be effective against curiosity/greed/malice, hopping sequences (FHSS) and spreading codes (DSSS) must be private In many implementations, these codes are given to all group members if becoming a group member is easy, there's no barrier If group membership is tightly guarded, can it be bought or stolen? If codes can't be obtained, can they be learned? Code reuse allows for statistical analysis and recovery 2015 Patrick Tague 29

30 Further Hardening the PHY If spread spectrum isn't enough, what else? Multiple diversity can protect against multiple threats at numerous levels Implementations must consider the threat models and adapt to unexpected behaviors Prevent statistical analysis, adapt to learning adversaries 2015 Patrick Tague 30

31 January 27: Physical Layer Security Assignment #1 Due 2015 Patrick Tague 31