6. Recv Secure Message

Hello, this is Blowing Nose.

 

In this session, we would like to explain the process of receiving a Secure Message.

The receiving process may be somewhat complex and challenging, but it is considered the most crucial flow in SecOC.

Firstly, today will be an introductory session to understand the overall procedure conceptually, for receiving the Secure Message.

 

 

1. Latest Fv

We store the Trip Counter and Reset Counter received through the Sync Message in the Latest Fv.

Detailed information about this can be found in section 3: Sync Message, so please refer to it if necessary.

 

2023.12.09 - [CyberSecurity/SecureOnCAN[Eng]] - 3. Sync Message

 

 

2. Recv Fv

In the previous session, we learned that Truncated Fv is transmitted by the Secure Message Sender.

The receiving side then receives this value and stores it in the Recv Fv.

 

 

3. Construct Fv

In the previous session, we learned that Construct Fv and Previous Fv are managed for each Secure Message.

Let's assume that 0x100 is a Secure Message, and the Construct Fv for 0x100 is created through the following three components.

• Recv Fv
• Latest Fv
• Previous Fv for 0x100

 

4. 16 Byte MAC Value Generation

Using Secure Msg 2Byte ID(0x01, 0x00 in this example), Construct Fv for 0x100 and the Key value, a 16-byte MAC value is generated through the AES128 function.

 

 

5. MAC Verification

Comparing the generated MAC value with the Truncated MAC value included in the Secure Message to check if they match. Since the Truncated MAC contains only a portion of the MSB (Most Significant Bits) from the entire 16-byte MAC, the comparison is done with only the corresponding MSB portion. When the MAC values match, the data is considered received successfully and can be used.

 

6. Update Previous Fv

When the MAC values match and the data is used for reception (Rx), the Construct Fv value is updated as the Previous Fv.

 

Today, we conceptually explained the receiving process. In the next session, we will delve into the implementation details of each step.

 

Thank you.