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Group-based Source Authentication in VANETs. You Lu, Biao Zhou, Fei Jia, Mario Gerla UCLA {youlu, zhb, feijia, gerla} VANET slide. VANET Scenario. The problem: authentication. VANET broadcast messages: Beacons for safe driving, surveillance, situation etc

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group based source authentication in vanets

Group-based Source Authentication in VANETs

You Lu, Biao Zhou, Fei Jia, Mario Gerla


{youlu, zhb, feijia, gerla}

vanet slide
VANET slide
  • VANET Scenario
the problem authentication
The problem: authentication
  • VANET broadcast messages:
    • Beacons for safe driving, surveillance, situation etc
  • Problem: malicious sources can generate bogus messages
    • Attack models
  • Critical issue we address here:
    • Sender authentication (within group)
    • Not addressed here:
      • Non repudiation
      • Privacy protection,
      • Secret delivery to selected group (e.g. police agents, taxi cabs, coalition members), etc
existing authent solutions
Existing Authent. solutions
  • PKI – a bit too expensive
  • TESLA – cheaper, but ..slow (Toyota et al)
tesla one way hash chain
TESLA: One Way Hash Chain
  • In TESLA a source generate a one way chain of length L by randomly picking the last element SL of the chain S and by repeatedly applying the Hash function F( ) to get the next values one after the other.
  • After creating the one way chain, the source stamps each packet with the chain values in reverse order. The receiver can verify Si+1 only after it receives Si from the source.
  • At this time, the receiver also verifies the source authenticity
tesla overview cont
TESLA overview (cont)
  • TESLA (Time efficient stream loss tolerant authentication)
    • Assumption: 2- time slot delay in authentication
      • Packet P1 received in slot 5; K5 received in slot 7
    • Authentication of P1:
      • Verify K5 from K4 pr K3 (explain how)
      • MAC(K5, P1) = Verify MAC
    • Pros: Robust to packet loss; Data all in plain text.
    • Con: delayed authentication.
exploit group motion to reduce latency
Exploit Group Motion to reduce latency
  • Group Scenario
    • Nodes move in groups
    • Each group is a closed broadcast group:
      • Military peace keeping patrols; police agents in a mission; presidential motorcade.
    • Group nodes acquire SECRET initial group attribute, and initial mobility counter before joining
  • Our Goal: reduce

the key disclosure

delay in group


group based source authentication gsa1
Group-based Source Authentication (GSA)
  • Protocol Design
    • How to define a group?
      • Group Identifier, such as group name, group ID…
      • Dynamic Attributes, such location intersection, group speed etc Must be better explained
      • Initial Group property is shared by the same group.
    • How to ensure disclosure key cannot be captured and replayed by attacker?
      • Encrypt the disclosure key with secret group ID.
      • External nodes cannot get K7,
      • secret group ID never transmitted in plain text.
      • Proactively updated dynamic attributed for extra security

Encrypt (K7, secret group ID)

step 1 group authentication
Step 1: Group Authentication
  • Group Authentication Phase
    • The sender broadcasts nonce with own GID and requests receivers in the group to authenticate themselves
    • Each Receiver R uses individual TESLA reverse hash chain.

Receiver Packet:

Time interval 3

    • After key disclosure delay period, each receiver sends K3
    • Sender checks if R is in the same group as itself.

Same Group member

    • Now all group members are authenticated and “in synch”
    • Periodically authenticate group membership after timeout
step 2 group based source authentication gsa
Step 2: Group-based Source Authentication (GSA)
  • Data Transfer Phase
    • Inter-group
      • Use conventional TESLA-like scheme (large latency)
    • Intra-group
      • Instant KEY disclosure
      • Packet sent at time i:
      • Group members:
        • decrypt K_i usinggroup_property key
        • verify Packet_i immediately using decrypted K_i.
  • Average End-to-End Latency:
  • Testbed: 7 Laptops with Intel M740 processor, 1.73 Ghz
  • Number of active GSA Sessions: from 5 to 500
experiments cont
Experiments (cont)
  • CPU and Memory Usage:
experiments cont1
Experiments (cont)
  • MAC Average Computing Time:
experiments cont2
Experiments (cont)
  • Performance Comparison of GSA and TESLA for single session:
  • GSA guarantees efficient, safe delivery of vehicular alarms within a group
  • GSA is applicable in the following scenarios:
    • Nodes move in group
    • Group nodes know initial group secret and initial mobility attributes
    • Incremental addition of attributes supported
  • Experiment results:
    • In TESLA, large latency due to key disclosure delay
    • GSA reduces key disclosure delay to significant groups (e.g., vehicles in the same convoy)
  • Future work:
    • Dynamic Group ID certificates to short lived urban vehicle platoons
    • Safety improvement resulting from of reduced latency
    • Secret content to selected groups (e.g., police)
    • Privacy preservation


Q & A