phc-discussions - RE: [PHC] Why protect against side channel attacks

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Message-ID: <CY1PR0301MB0668AE97DB5FE5825C4101C2ACAE0@CY1PR0301MB0668.namprd03.prod.outlook.com>
Date: Thu, 25 Jun 2015 00:48:22 +0000
From: Greg Zaverucha <gregz@...rosoft.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: RE: [PHC] Why protect against side channel attacks

You’re right there is a way to recover by resetting all the passwords, but this is the worst-case thing to have to do.  I was comparing this to an algorithmic attack on the PHF (like a TMTO), where you can just re-hash with stronger parameters.

If a company gets complaints of PWNed accounts and their PHF has side-channel protections, the investigation of how the accounts got PWNed is simpler.

Greg

From: Bill Cox [mailto:waywardgeek@...il.com]
Sent: Wednesday, June 24, 2015 5:33 PM
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Why protect against side channel attacks

On Wed, Jun 24, 2015 at 5:18 PM, Greg Zaverucha <gregz@...rosoft.com<mailto:gregz@...rosoft.com>> wrote:
Yes I (and others, like you Krisztián) have understood the technical mechanics of how the attack would work for a while.  But I hadn't thought through the whole scenario that I described in my email, and the part that was new to me was that there isn't a good way to recover from this type of attack...

To recover from a cache-timing attack where the attacker has the salt and usernames, you can simply require users to reset passwords, just like we do normally.  This gives you a new password/salt database, which should be better protected in the future.

I am confused why a company would more easily learn of a password database leak than a cache timing attack combined with leaking the salt database.  The usual signal a company notices first is a ton of complaints from users with PWNed accounts.

Bill

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