I did not implement it yet.  It would go in Command task.c and replace or perhaps duplicate the authenticate function.

Feel free to code it.  

I don't know if we will ultimately go this way.  I would still like to make the AES authentication work but I agree this could be simpler and faster.  So it would be good to test it.

Chris 

On Fri, Sept 15, 2023, 11:20 Corey Minyard <minyard@acm.org> wrote:

On Fri, Sep 15, 2023 at 10:06 AM Chris Thompson via pacsat-dev
<pacsat-dev@amsat.org> wrote:
>
> Ok, thanks for that Corey.  Very interesting.  We may not be susceptible to the length extension attack vulnerability though.  If I understand correctly, then a message sent as: Hash( key + "Watch the enemy") could be manipulated to Hash(key + "Watch the enemy and attack them after 5 mins"), without knowing the key.  But our commands are fixed at 18 bytes length (for now at least). So any extra appended message would be ignored.  With that said, it may not be much harder to implement the scheme as described.

Yes, I was more worried about the "various security papers have
suggested vulnerabilities with this approach" comment in the article
on the key || message || key approach.  It probably means there are
other issues with the approach, possibly key extraction attacks.  The
HMAC approach seems generally more cryptographically sound.

I was going to say that I could implement it, though it's pretty
trivial.  You've probably already done it :).

-corey - AE5KM

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