roadside units and vehicles embedded on-board modules • VANET vehicles collect and broadcast various data • Data include the road condition, traffic jams, accidents, abnormal weather condition etc.. • Representatively VANET has three model. But we will use reputation-based in this seminar Fundamental of VANET
the other vehicles through a roadside unit or an ad-hoc network • Message evaluation vehicle (MEV) The MEV receives traffic information (TI) along with the sender’s reputation record and decides whether • Reputation management server (RMS) The RMS receives evaluation messages from the vehicles and classifies and accumulates the messages for each of the vehicles Fundamental of VANET
location, etc… at their broadcasting message • Attack on reputation message Same with attacks on privacy, but, attack reputation message • Attacks on evaluation message If attacker broadcast false TI, then do not update reputation value, attacker can maintain good reputation value Or attacker can try to add good evaluation message multiple times to improve its reputation record Kind of threat and privacy issue
of reputation values Reputation value must not be forged • Robustness against denial of update Adversary may try to skip reputation update process after sending unreliable information, so, we have to force to update • Robustness against reply attack Adversary may send positive or negative evaluation message multiple times for forge another’s reputation value Kind of threat and privacy issue
states that, given and for uniformly and independently chosen a, b ∈ , the value looks a random element in -This intuitive notion is formally stated by the following two probability distributions which are computationally indistinguishable (in the security parameter, n = log(q)) : (, b, ab), where and are randomly and independently chosen from (, , ), where , , are randomly and independently chosen from • Definition 2. Bilinear map • Definition 3. Decisional bilinear Diffie-Hellman problem (DBDH) Preliminaries
- Register - Receive initial RV and certificate - Generate Pseudonyms - ( , ) Broadcasts 2. Receiving TI - Verify RV using session notification - Check 4. Update - Server accumulates for each MBV with next session secret - MBV retrieve it and update 3. Sending - Evaluate TI - Create and send (, )
(, , , ) • RMS generates a public/private key pair, ∈ , = • It chooses ∈ , and hash functions ∙ : 0,1 ∗ → • The global parameters are , , , , ∙ How it works
• Vehicle can make pseudonym in every session with UID • A MBV generates a temporary key , picks a random number , encrypts it with the public key of RMS: ⋅ , • The MBV sends , ⋅ , to RMS as meaning of joining • If the is valid and not exist, the RMS generates a default reputation value and computes a signature of it • = , , where ∈ is session secret of current session • The RMS sends , , and { } to the vehicle. • The MBV first generates a pseudonym to preserve the privacy. The MBV computes its pseudonym , and validity information : = , = ⋅ How it works
verify a validity of receiving Reputation value • The RMS manages a session and it issues a session notification value ′ = (, ⋅), where ∈ • The MBV broadcasts the TI with the pseudonym, the validity information, the reputation value, and signed reputation: , , , • A vehicle receives the TI and wants to check validity of pseudonym, it can be verified as follows: , ? = ( , ) • And then the receiving vehicle first checks the reliability of the TI using the reputation value. If it is high enough, the vehicle can verify the validity of the reputation value as follows: ′, ? = ⋅ • If the equation is valid, then the vehicle accepts the message, otherwise it rejects How it works
a evaluation message ∈ 0,1 • If the TI is reliable, = 1 but, if the TI is unreliable, = 0 • The MEV computes ( | for the integrity and sends , , , ( ||) with its reputation value to the RMS • The RMS checks validity of the evaluation message. If verified its validity, the RMS accepts the evaluation message How it works
without revealing the vehicle’s privacy • Find accumulated value from RMS and merge it to their reputation value • If vehicle against update, it cannot pass the verification process • Update process is : ′ = + ′ = ⋅ ⋅ = , ⋅ ⋅ ⋅ , ⋅ +1⋅ = , ⋅ +1⋅′ How it works
Suppose there exist pseudo random generators (PRGs) that have robustness against polynomial-size circuits. Then, a functional pseudonym created with a random number that is generated by the PRG has the polynomial-time indistinguishability under DDHP • An attacker can’t reveal target’s UID from set of pseudonyms • It is computationally difficult for the attacker who has similar level of computing ability as a normal vehicle Analysis and Conclusion
merge accumulated evaluation messages repeatedly at the reputation phase. If didn’t do it, they cannot pass the verification process • If attacker try to use another vehicle’s reputation value, attacker will be blocked unless it obtain UID or () • A reputation value which has not been updated cannot pass the verification process of the broadcasting traffic information phase Analysis and Conclusion
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