Re: [PATCH 0/6] Constant Time Memory Comparisons Are Important

[Emmanuel Grumbach]

On Sun, Jun 11, 2017 at 4:36 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Sun, Jun 11, 2017 at 1:13 AM, Kalle Valo <kvalo@xxxxxxxxxxxxxx> wrote:
> > "Jason A. Donenfeld" <Jason@xxxxxxxxx> writes:
> >
> >> Whenever you're comparing two MACs, it's important to do this using
> >> crypto_memneq instead of memcmp. With memcmp, you leak timing information,
> >> which could then be used to iteratively forge a MAC.
> >
> > Do you have any pointers where I could learn more about this?
>
> While not using C specifically, this talks about the problem generally:
> https://www.chosenplaintext.ca/articles/beginners-guide-constant-time-cryptography.html
>

Sorry for the stupid question, but the MAC address is in plaintext in
the air anyway or easily accessible via user space tools. I fail to
see what it is so secret about a MAC address in that code where that
same MAC address is accessible via myriads of ways.