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

2017-06-11 22:48 GMT+02:00 Emmanuel Grumbach [off-list ref]:

On Sun, Jun 11, 2017 at 4:36 PM, Kees Cook [off-list ref] wrote:

quoted

On Sun, Jun 11, 2017 at 1:13 AM, Kalle Valo [off-list ref] wrote:

quoted

"Jason A. Donenfeld" [off-list ref] writes:

quoted

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.

I think you're mixing up Media Access Control (MAC) addresses with
Message Authentication Code (MAC). The second one is a cryptographic
signature of a message.