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Date: Thu, 25 Jun 2015 00:48:22 +0000
From: Greg Zaverucha <>
To: "" <>
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.


From: Bill Cox []
Sent: Wednesday, June 24, 2015 5:33 PM
Subject: Re: [PHC] Why protect against side channel attacks

On Wed, Jun 24, 2015 at 5:18 PM, Greg Zaverucha <<>> 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.


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