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From: Emmanuel Grumbach <egrumbach@gmail.com>
Date: Sun, 11 Jun 2017 23:48:36 +0300
Message-ID: <CANUX_P2b0Bx+-E_OBQ0reGW0=d6819qc=r83K0kTv0xMo8mtLQ@mail.gmail.com>
Subject: Re: [PATCH 0/6] Constant Time Memory Comparisons Are Important
To: Kees Cook <keescook@chromium.org>
Cc: Kalle Valo <kvalo@codeaurora.org>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "kernel-hardening@lists.openwall.com"
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On Sun, Jun 11, 2017 at 4:36 PM, Kees Cook <keescook@chromium.org> wrote:
>
> On Sun, Jun 11, 2017 at 1:13 AM, Kalle Valo <kvalo@codeaurora.org> wrote:
> > "Jason A. Donenfeld" <Jason@zx2c4.com> 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.