Return-path: Received: from mail-oi0-f67.google.com ([209.85.218.67]:33947 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751794AbdFKUsi (ORCPT ); Sun, 11 Jun 2017 16:48:38 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170610025912.6499-1-Jason@zx2c4.com> <878tkzq6wi.fsf@purkki.adurom.net> From: Emmanuel Grumbach Date: Sun, 11 Jun 2017 23:48:36 +0300 Message-ID: (sfid-20170611_224922_624993_00BA0090) Subject: Re: [PATCH 0/6] Constant Time Memory Comparisons Are Important To: Kees Cook Cc: Kalle Valo , "Jason A. Donenfeld" , LKML , "kernel-hardening@lists.openwall.com" , Anna Schumaker , David Howells , David Safford , "David S. Miller" , Gilad Ben-Yossef , Greg Kroah-Hartman , Gustavo Padovan , "J. Bruce Fields" , Jeff Layton , Johan Hedberg , Johannes Berg , Marcel Holtmann , Mimi Zohar , Trond Myklebust , keyrings@vger.kernel.org, linux-bluetooth@vger.kernel.org, "open list:NFS, SUNRPC, AND..." , linux-wireless , Network Development Content-Type: text/plain; charset="UTF-8" Sender: linux-wireless-owner@vger.kernel.org List-ID: On Sun, Jun 11, 2017 at 4:36 PM, Kees Cook wrote: > > On Sun, Jun 11, 2017 at 1:13 AM, Kalle Valo wrote: > > "Jason A. Donenfeld" 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.