# A Low-Overhead Message Authentication and Secure Message Dissemination Scheme for VANETs
## 3 Proposed Approach
### Proposed Method
```
When \(v\) enters the region covered by a \(GL\): Receives proof of leadership message \(E((^{\ast}Leader^{\prime\prime},PU_{GL},ts),PR_{RSU})\) from the \(GL\); Retrieves \(PU_{GL}\) from the encrypted message using \(PU_{RSU}\);  Computes \(M_{1}=(^{\ast}Join^{\ast},ts)\);  Encrypts \(M_{1}\) using public key of Group Leader \(PU_{GL}\)  Sends \(M_{1}^{\prime}=(PID_{v},GL,E(M_{1},PU_{GL}),Cert_{v},SIG_{v})\) to \(GL\), where \(SIG_{v}=E(H(M_{1}),PR_{v})\);  When a \(GL\) receives \(M_{1}^{\prime}\) from \(v\):  Decrypts \(M_{1}^{\prime}\) using \(PR_{GL}\)  Verifies \(Cert_{v}\) using \(PU_{DMV}\);  Verifies the signature using \(PU_{v}\);  If verification succeeds{  Computes \(M_{2}=(^{\ast}Accept^{\prime\prime},K,ts)\); // \(M_{2}\) contains the acceptance of \(GL\) for \(v\); // \(K\) is a symmetric key between \(v\) and \(GL\) for further // communication;  Encrypts \(M_{2}\) using public key \(PU_{v}\) of \(v\) ;  Sends \(M_{2}^{\prime}=(GL,PID_{v},E(M_{2},PU_{v}),SIG_{GL})\) to \(v\),  where \(SIG_{GL}=E(H(M_{2}),PR_{GL})\));  Else { Discards \(M_{2}\);} When \(v\) receives \(M_{2}^{\prime}\) from the \(GL\):  Decrypts \(M_{2}^{\prime}\) to obtain \(M_{2}\);  Verifies \(SIG_{GL}\) using \(PU_{GL}\);  If verification succeeds{  Stores (\(M_{2}\));}  Else { Discards \(M_{2}\);}
```  
**Algorithm 3**When vehicle \(v\) enters a sub-region covered by a Group Leader \(GL\)  
**When a vehicle \(v\) wants to send a message \(M\) to its \(GL\):** When \(v\) wants to send a message \(M\) about an observed event to its \(GL\), it signs and encrypts \(M\) and sends \(M_{1}\) to the \(GL\), where \(M_{1}=(PID_{v},GL,E((M,ts),K),SIG_{v})\); here, \(ts\) is the timestamp, \(K\) is the symmetric key established between \(v\) and \(GL\), and \(PID_{v}\) is the pseudo-ID of \(v\). When \(GL\) receives \(M_{1}\), it decrypts the message using the symmetric key \(K\) and checks the freshness of the message using the \(ts\). It uses a signature \(SIG_{v}\) to verify the authenticity and integrity of the message. Then, the \(GL\) aggregates the received message with the messages received from other vehicles in its sub-region and forwards the aggregated message to the \(RSU\), and the \(RSU\) can further aggregate messages received from other \(GL\)s in its region and disseminate them to the appropriate sub-regions of its region or regions covered by other \(RSU\)s. Algorithm 4 shows this message collection and dissemination process. ``` When a vehicle \(v\) wants to send a message \(M\) about an observed event: \[\text{Computes }M_{1}=(PID_{v},GL,E((M,ts),K),SIG_{v})\text{;}\] \[\text{Sends }M_{1}\text{ to }GL\text{;}\] \[\text{// }K\text{ is the symmetric key established in the}\] \[\text{// Algorithm 3}\text{.}\] When the \(GL\) receives \(M_{1}\) from \(v\): \[\text{Decrypts }M_{1}\text{ using the symmetric key }K\text{ and retrieves}\] \[\text{the message }M\text{;}\] \[\text{Chercks the timestamp }ts\text{;}\] \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]0 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]1 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]2 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]3 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]4 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]5 When the \(RSU\) receives \(M_{2}\) from \(GL\): \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]6 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]7 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]8 \[M_{1}=(RSU,PID_{v},(E(\"Accept\",K,ts),PU_{v}),Cert_{RSU},SIG_{RSU}),\]9 \[SIG_{RSU}=E(H(\"Accept\",K,ts),PR_{RSU}).\]0 \[SIG_{RSU}=E(H(\"Accept\",K,ts),PR_{RSU}).\]1

**Certificate Revocation List (CRL) distribution and certificate revocation process. ** Misbehaving vehicles can send malicious messages to other vehicles; these misbehaving vehicles should be detected and punished.