Can csec key11~17 update other keys as auth key?

[yaojianhang]

Hi,

I'm using S32K144, trying to use CSEc key11~17 update oher keys, since M1 message's Auth ID is 4 bit and doesn't have 1 bit KBS as KeyID. It seems impossible to do this.

[lukaszadrapa]

Hi @yaojianhang 

let me share some screenshots:

From the reference manual:

 In application note AN5401:

In source files of AN5401:

And regarding the second question, this can be found in AN5401:

This is given by SHE specification. RAM_KEY can be updated anytime, you do not need to know MASTER_ECU_KEY or previous value of the RAM_KEY.

Regards,

Lukas

[yaojianhang]

HI,@lukaszadrapa 

In this code，use CSEC_KEY_11 updates CSEC_KEY_11 return  ERC_KEY_INVALID, use MASTER_ECU_KEY updates CSEC_KEY_11 return no error.

How to use CSEC_KEY_11 updates CSEC_KEY_11? Is it possible?  Thanks for you reply.

Regards,

yaojianhang.

 

[lukaszadrapa · Accepted solution]

Hi @yaojianhang 

that's very good point. I did some debugging on my side and I found out that there's a bug in the calculate_M1_to_M5 function.

I already mentioned this code:

key_id = key_id & 0x0F; //For keys in the other bank, don't consider the KBS bit in M1 & M4 calculation. Follow traditional SHE specs

However, this is not enough. Also AuthID should be modified in the same way when calculating M1 and M4. From AN5401:

And:

So, I added this code:

auth_key_id = auth_key_id & 0x0F;

... and everything works as expected now.

Thank you for pointing this out, I will report it.

Regards,

Lukas

[yaojianhang]

Thanks!

Regards,
yaojianhang

[yaojianhang]

additions:

can CSEc key11~17 update themselves and ram_key?