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Wireless Network Security and Sensor Networks. Topics. Brief review of wireless security Sensor networks: Architecture and Issues of Security of SNs SNEP  Tesla. 802.11. 802.11 a, b, … Components Wireless station A desktop or laptop PC or PDA with a wireless NIC. Access point

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Presentation Transcript
  • Brief review of wireless security
  • Sensor networks: Architecture and Issues of
  • Security of SNs
    • SNEP
    • Tesla
802 11
  • 802.11 a, b, …
  • Components
    • Wireless station
      • A desktop or laptop PC or PDA with a wireless NIC.
    • Access point
      • A bridge between wireless and wired networks
        • Radio
        • Wired network interface (usually 802.3)
        • Bridging software
      • Aggregates access for multiple wireless stations to wired network.
802 11 modes
802.11 modes
  • Infrastructure mode
    • Basic Service Set
      • One access point
    • Extended Service Set
      • Two or more BSSs forming a single subnet.
    • Most corporate LANs in this mode.
  • Ad-hoc mode (peer-to-peer)
    • Independent Basic Service Set
    • Set of 802.11 wireless stations that communicate directly without an access point.
      • Useful for quick & easy wireless networks.
infrastructure mode
Infrastructure mode

Access Point

Basic Service Set (BSS) –

Single cell


Extended Service Set (ESS) –

Multiple cells

ad hoc mode
Ad-hoc mode

Independent Basic Service Set (IBSS)

802 11b security services
802.11b Security Services
  • Two security services provided:
    • Authentication
      • Shared Key Authentication
    • Encryption
      • Wired Equivalence Privacy
wired equivalence privacy
Wired Equivalence Privacy
  • Shared key between
    • Stations.
    • An Access Point.
  • Extended Service Set
    • All Access Points will have same shared key.
  • No key management
    • Shared key entered manually into
      • Stations
      • Access points
      • Key management a problem in large wireless LANs
wep sending
WEP – Sending
  • Compute Integrity Check Vector (ICV).
    • Provides integrity
    • 32 bit Cyclic Redundancy Check.
    • Appended to message to create plaintext.
  • Plaintext encrypted via RC4
    • Provides confidentiality.
    • Plaintext XORed with long key stream of pseudo random bits.
    • Key stream is function of
      • 40-bit secret key
      • 24 bit initialisation vector
  • Ciphertext is transmitted.
wep encryption
WEP Encryption





Vector (IV)



Key Stream


Secret key



32 bit CRC



wep receiving
WEP – Receiving
  • Ciphertext is received.
  • Ciphertext decrypted via RC4
    • Ciphertext XORed with long key stream of pseudo random bits.
  • Check ICV
    • Separate ICV from message.
    • Compute ICV for message
    • Compare with received ICV
shared key authentication
Shared Key Authentication
  • When station requests association with Access Point
    • AP sends random number to station
    • Station encrypts random number
      • Uses RC4, 40 bit shared secret key & 24 bit IV
    • Encrypted random number sent to AP
    • AP decrypts received message
      • Uses RC4, 40 bit shared secret key & 24 bit IV
    • AP compares decrypted random number to transmitted random number
  • First tool to demonstrate attack using IV weakness.
    • Open source
  • Three components
    • Weaker IV generator.
    • Search sniffer output for weaker IVs & record 1st byte.
    • Cracker to combine weaker IVs and selected 1st bytes.
  • Automated tool
    • Does it all!
    • Sniffs
    • Searches for weaker IVs
    • Records encrypted data
    • Until key is derived.
  • Security Policy & Architecture Design
  • Treat as untrusted LAN
  • Discover unauthorised use
  • Access point audits
  • Station protection
  • Access point location
  • Antenna design
bluetooth security
Bluetooth Security
  • Mode 1 – non-secure.
  • Mode 2 – service level enforced security.
    • Initiated after the channel is established.
  • Mode 3 – link level enforced security
    • Initiated before the channel is established.
  • Trusted Devices
    • Unrestricted access to all services.
  • Untrusted Devices
    • Services requiring Authorisation and Authentication.
    • Services requiring Authentication.
    • Open services.
link layer services
Link Layer services
  • Link Layer
    • Authentication of Peers
    • Encryption of information
  • Unique public device address
    • BD_ADDR
    • 48 bits, allocated by IEEE
connecting two devices
Connecting Two Devices
  • Two devices with no prior connection
    • For low security connections
      • 128 bit Unit link key from one device used.
      • Created when device is manufactured.
    • For higher security connections
      • 128 bit Combination link key generated
      • Provides
        • Confidentiality
        • Integrity
        • Authentication
combination key
Combination Key
  • Identical PIN code entered into both devices.
  • 128 bit initialisation link key generated.
      • PIN code
      • Device Address
      • Random number
  • Combination key now generated.
  • Combination key stored for future use.
wireless transport layer security wtls
Wireless Transport Layer Security (WTLS)
  • Provides security services between the mobile device (client) and the WAP gateway
    • Data integrity
    • Privacy (through encryption)
    • Authentication (through certificates)
    • Denial-of-service protection (detects and rejects messages that are replayed)
wap gateway architecture
WAP Gateway Architecture








wtls record protocol
WTLS Record Protocol
  • Takes info from the next higher level and encapsulates them into a PDU
    • Payload is compressed
    • A MAC is computed
    • Compressed message plus MAC code are encrypted using symmetric encryption
    • Record protocol adds a header to the beginning to encrypted payload
alert protocol
Alert Protocol
  • Convey WTLS-related alerts to the peer entity
  • Alert messages are compressed and encrypted
  • A fatal warning terminates the connection (i.e. incorrect MAC, unacceptable set of security parameters in the handshake
  • Certificate problems usually cause a non-fatal error
ssl vs wtls
  • Datagram support ( UDP)
  • Expanded set of alerts
  • Optimized handshake – 3 levels of client/server authentication
  • New Certificate Format – WTLS certificates are small in size and simple to parse
  • Support client identities
  • Additional cipher suites – RC5, short hashes
  • Explicit shared secret mode
sensor network

Sensor Network

What is it?

what and where when
What and Where/When
  • What?
    • Low cost, low power, multi-functional sensor nodes
    • Communicates within short distances
    • Enabled by MEMS, wireless, and digital electronics
  • Where:
    • Military, health, environmental
ad hoc networks vs sns
Ad hoc Networks vs. SNs
  • Number of nodes several orders larger
  • Densely deployed
  • More prone to failures
  • Dynamic topology (frequent changes)
  • SNs use broadcasts instead of PP
  • Power, CPU, and memory limitations
  • No global IDS
  • Military
    • c4ISRT, NBC detection etc.
  • Environmental
    • Forest fire, bio-complexity analysis, flood detection
  • Health
    • Tele-monitoring, tracking, drug admin.
  • Commercial
    • Environmental control of office buildings
      • Potential for $55B/year saving &, reduction of 35 mmt of CO2 emission
    • Detection of vehicle thefts (Not Really SensorNets..)
    • Inventory control (Mostly RFIDs not nets)
design goals
Design Goals
  • Fault tolerance
  • Scalability
  • Cost ~= $1/node
    • (what do batteries cost? )
  • Hardware constraints
  • Transmission constraints
  • Power constraints
  • SWAP (Size Weight and Power) critical for military apps
sensor networks overview
Sensor Networks Overview
  • Sensor Nodes
    • Sensor networks are made up of large number of ad hoc sensor nodes
      • Power supply
      • Memory
      • Sensing hardware
      • Data processing
      • Communication components
sensor networks overview cont
Sensor Networks Overview (cont.)
  • Sensor networks communication architecture
    • Sensor nodes and sink node (Monitoring Station)
    • Each of these scattered sensor nodes has the capabilities to collect data and route data back to the Monitoring Station
sensor networks overview cont1
Sensor Networks Overview (cont.)
  • Procedure
    • The source starts transmitting data packets toward the sink (a)
    • When a node joins the network it starts transmitting and receiving packets and sending a neighbor announcement message (b)
    • When the process completes, the group of newly active neighbors that have joined the network make the delivery of data from source to sink more reliable (c)
  • Self-organizing sensor networks topology
    • Alberto Cerpa and Deborah Estrin 2002
sensor networks cont
Sensor Networks (cont.)
  • 4 State transitions of sensor nodes

When a node starts, it initializes in theteststate; it sets up a timer Tt. When Tt expires, the node enters the active state; Before Tt expire, the number ofactiveneighbors > the neighbor threshold (NT),the node moves to passive state;

When a node enters the passive state, it sets up a timer Tp. When Tp expires, the node enters thesleep state. Before Tp expire, , the number of neighbours is < NT(…), the node moves to teststate;

When a node enter thesleep turns the radio off, sets a timer Ts and goes tosleep.When Ts expires, the node moves intopassive state.

area monitoring
Area Monitoring
  • Jean Carle et al paper, 2003
  • 3 sub problems for area monitoring
    • Select sensors that are needed for area coverage, other sensors to sleep mode - to reduce the number of sensor needed to monitor the area to extend network life;
    • Construct broadcasting tree from monitoring station to all active sensors: minimum energy broadcasting or dominating set based;
    • Sensors report events to monitoring station using reverse broadcast tree.
area coverage algorithm 1
Area Coverage - Algorithm 1
  • Ye, Zhong,Chen, Lu, Zhang 2003
    • A sensor sleeps for a while, then decides to be active iff there is no active sensor closer than a threshold distance
    • Onceactive, it remains active until life ends
    • Non-active periodically reevaluates decision
    • High probability of full coverage if threshold < ≈ 0.3 sensing radius
  • The disadvantage
    • Probabilistic not ensure the full coverage
area coverage algorithm 2
Area Coverage - Algorithm 2
  • Tian 2002
    • Each sensor knows position of all neighbors
    • If neighbors cover its sensing area then sensor sends withdrawal message after timeout = negative acknowledgement (goes to sleep mode)
    • Otherwise, remain active
    • Repeats periodically
    • Neighbor sensors may disappear without notice
    • Covering sensors may not be connected
  • Require priori knowledge of all neighboring nodes
area coverage algorithm 3
Area Coverage - Algorithm 3
  • Carle, Simplot, Stojmenovic, 2003
    • Area dominating set algorithm
    • Covered = active neighbors are connected and together cover its sensing area
    • If not covered at end of timeout then send positive ack, otherwise send negative ack
    • Positive and negative ack variant
    • Positive only acks variant

(shorter network life)

Central node decides to be non-dominant (sleep)

Central node decides to be dominant (active)

(area is covered by active neighbors

but these neighbors are not connected)

area coverage algorithm 3 cont
Area Coverage - Algorithm 3 (Cont.)
  • The Election of Covering Nodes

E.g. Nodes 0,1,2,3,4 are active,Node 5 decides to be inactive

    • If node 5 does not announce its deactivation,
      • Node 6 decides to be active
    • Else, node 5 announce its status
      • Node 6 decides to be inactive
  • Negative ack may reduce the number of active sensors (prolong network life)
  • Experiments show that “positive and negative ack” leads to four times smaller area dominating sets than “positive only ack” for dense networks.
broadcasting monitoring station to sensors
Broadcasting - Monitoring Station to Sensors
  • Distribute requests from monitoring station to the whole sensor nodes
  • Broadcasting is a common and important operation for route finding, information dissemination or request diffusion
  • Research on energy efficient broadcast protocols
  • Aim at reducing the number of sensors which participate in broadcasting
broadcasting tree i monitoring station to sensors
Broadcasting Tree (I)- Monitoring Station to Sensors
  • F.Dai and J.Wu, 2003
    • Dominant punning scheme
    • Applied on area dominant set
    • The dominant punning method is the same process as constructing area dominant set
    • 20% reduction with most of saving the border of monitored area according to the experimental data
broadcasting tree ii monitoring station to sensors
Broadcasting Tree (II)- Monitoring Station to Sensors
  • A.Qayyum, et al. Multipoint Relay (MPR) Protocols
    • Select a minimal set of one-hop neighbors that cover the same network as the complete set of neighbors
    • Each node find its relay set
    • Repeats periodically, add to the relay subset the neighboring node which covers
    • The list of relay nodes are attached to the retransmitted packet
    • Applied on area dominating sets, MPR constructs relay subsets which contain nearly all nodes
reporting events sensors to monitoring station
Reporting Events – Sensors to Monitoring Station
  • Sensor measurements – sensors report only important information (data aggregation)
  • Spanning tree induced by flooding over area dominating set (reduce the number of sensors and energy saving)
  • Ruiz, L.B, et al, 2003
  • Three-layer sensor networks management architecture
  • Service - Executed by a set of function;
  • Management functions - Five possible states: ready, not-ready, executing, done, and failed;
  • Wireless sensor networks Models – Dynamic in time
management cont
Management (cont.)

Sensor nodes differ in their hardware physical capabilities

  • Manager –Collects and distribute information from all agents and controls the entire networks
  • Sink node–Host an intermediate manager
  • Agent – Raise some questions related to the location nodes
management cont1
Management (cont.)

Agents in hierarchical homogeneous

  • Manager - Collects and distribute information from all agents and controls the entire networks
  • Agent - Raise some questions related to the location nodes
  • Cluster-head - Response for sending data to a base station; execute correlation of management data (no sink node)
  • Base Station- Connect, communicate and secure networks
sensor network security
Sensor Network Security
  • What do we mean by sensor network security?
    • Conventional view of security from cryptography community: cryptographically unbreakable design in practical sense
    • Network Reality: very few security breaches in practice are to exploit flaws in cryptographic algorithms; side channel attacks
  • Malicious versus selfish (DoS vs. resource gobbler)
  • Security v.s. robustness, fault tolerance, resiliency
  • Security is not a black/white world, it is progressive
  • We must secure entire networked system, not just an individual component
  • Solutions must be robust/adapt to new threats as much as possible
how is it different
How is it Different?
  • Wireless Sensor networks have NO clear line of defense
    • Each node is a host as well as a “router”
    • Security solutions in wired or cellular networks may leverage the networking infrastructure
    • Secure Network/service “infrastructure” has to be collaboratively established
  • Wireless channel is easily accessible by both good citizens and attackers
  • Resource constraints on portable devices
    • Energy, computation, memory, etc.
    • Some devices may be compromised
    • Heterogeneity prevents a single security solution

Capability based Abstraction of a Heterogeneous Network

Capability-based Abstraction





BN-Backbone node

RN-Regular Node












incomplete list of challenges
Incomplete list of challenges
  • Resource-Efficient Secure Network Services
    • Network Initialization, single/multihop neighbor discovery
    • Multihop path establishment & Routing
    • Supporting application services
  • Cryptographic services
    • Broadcast authentication
    • Key management
  • Security mechanisms for fundamental services
    • Clock synchronization
    • Secure location discovery and verification of claims
    • Location privacy
    • Secure aggregation and in-network processing
    • Cluster formation/cluster head election
    • Middleware (will not discuss further)
incomplete list of challenges1
Incomplete list of challenges
  • Modeling vulnerabilities
    • VERY POOR state of understanding
    • Needed by services and applications
  • Cross-layer design techniques
    • Routing/location-aware protocols that are also robust!
    • Incorporating semantics such as geometry, radio model and range for context-based security
    • Functionality instead of optimality
problem 1 robust designs
Problem #1: Robust Designs
  • Attacks and compromise of network are reality
    • Misconfiguration cannot be fully eliminated
    • Maybe we can never enumerate
    • Software bugs are #1 cause for all possible attacks
    • Not every device can implement maximum-strength solutions
  • Shift from prevention to tolerance
    • Building trustworthy system out of untrustworthy components
    • Ability to detect, and function, even in the presence of problems
    • Similar analogy to IP
      • building reliable system out of unreliable components
    • How? Can be application specific
problem 2 adaptive security
Problem #2: Adaptive Security
  • Adaptation to handle many dimensions of dynamics:
    • Adaptive to user requirements
      • Differential security services used in government and military
    • Adaptive to user devices
    • Adaptive to channel dynamics:
      • Partial connectivity, disconnectivity, full connectivity
    • Adaptive to mobility
      • Cross-domain service for roaming users
    • Adaptive to dynamic membership
      • Node join, leave, fail
problem 3 joint design of qos and security
Problem #3: Joint Design of QoS and Security
  • Incorporating network metrics and security: scalability, communication overhead, computation complexity, energy efficiency, device capability, …
  • Different performance metrics may be in (partial) conflict
    • Probably the most secure system is of minimal usability
    • Example: energy efficiency/computation complexity versus cryptography strength
  • Many conventional security solutions take a centralized approach

Problem #4: Evaluation of Design

  • Current designs have an explicit threat model in mind
    • NOT Realistic
    • Real trace analysis for practical attacks?
  • Benchmarking ?
    • Other areas in computer systems have well defined benchmarks: SPEC CPU, TPC-C
  • Analytical tools
    • Current effort: game theory, graph theory
problem 5 securing the chain
Problem #5: Securing the Chain
  • The system is only as secure as the weakest link
    • Many supporting components: DNS, ARP, DHCP,…
    • Other supporting protocols: bootstrapping, discovery, time synchronization
  • How to secure these supporting components
    • Often ignored
    • Secure the entire system chain
  • Build multiple fences
    • Each fence is built based on a component’s resource constraint
security in sensor networks
Security in Sensor Networks
  • To provide
    • Confidentiality
    • Authenticity, integrity
    • Timeliness – freshness
  • With minimum power consumption
    • Minimize communication – key exchanges
    • Private key encryption
trust model
Trust Model
  • Sensor Nodes are not trusted
  • Sink node part of the trusted network
  • Sink node and the sensor nodes share secret
  • Node trusts its own resources
    • Clock, memory etc.
spin two protocols
SPIN – Two Protocols
  • Secure Network Encryption Protocol (SNEP)
    • Provides confidentiality, authentication, freshness between endpoints
  • µTESLA - Micro Timed Efficient Stream Loss-tolerant Authentication
    • Provides broadcast authentication
snep basics
SNEP Basics
  • Private key encryption
    • DES-CBC
    • Derive subsequent keys from the original shared key using RC5
    • Use counter mechanism for freshness

{Msg}<Kencr, Counter>, MAC(KMAC, Counter | {Msg}<Kencr, Counter>)

Confidentiality with authentication MAC

  • Provides authentication for broadcast
  • In general needs public-key system to avoid forgery
  • Public-key not suitable for SNs
  • Emulate public-key using delayed private key disclosure (see details in SPIN paper)
wireless sensor network references
Wireless/Sensor Network References
  • Adrian Perrig, Robert Szewczyk, Victor Wen, David Culler, J. D. Tygar. SPINS: Security Protocols for Sensor Networks. Mobile Computing and Networking, 2001.
  • Jiejun Kong, Petros Zerfos, Haiyun Luo, Songwu Lu, Lixia Zhang. Providing Robust and Ubiqitous Security Support for Mobile Ad-Hoc Networks. 9th International Conference on Network Protocols, Nov. 2001.
  • Haiyun Luo, Songwu Lu. Ubiquitous and Robust Authentication Services for Ad Hoc Wireless Networks. Technical Report UCLA-CSD-TR-200030, University of California, Los Angeles. October 2000
  • Akyildiz, I.F., Su, W., Sankarasubramaniam, Y., and Cayirci, E., ``A Survey on Sensor Networks,” IEEE Communications Magazine, Vol. 40, No. 8, pp. 102-116, August 2002