phc-discussions - Re: [PHC] How important is salting really?

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Message-ID: <20141212033047.29e503db@lambda>
Date: Fri, 12 Dec 2014 03:30:47 +0000
From: Brandon Enright <bmenrigh@...ndonenright.net>
To: Marsh Ray <maray@...rosoft.com>
Cc: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>,
 bmenrigh@...ndonenright.net
Subject: Re: [PHC] How important is salting really?

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On Fri, 12 Dec 2014 01:21:32 +0000
Marsh Ray <maray@...rosoft.com> wrote:

> C.      Prevents the trivial determination that two accounts chose
> the same password

There are special cases where this point comes into play.  For example,
in the recent Adobe breach an unknown "personalization key" (actually
an encryption key in this case) was used which made cracking
impossible.  But, because of a lack of salting (or in this case CBC +
random IV) it was still possible to determine the password for a large
number of the accounts because the password hints were also leaked.

Salting protects against being able to use information gleaned from
other accounts (like a password hint) from being useful.

I think *everyone* should be using a personalization key with whatever
hashing scheme they pick because without the personalization key a
database leak is nearly harmless.  If the personalization key leaks with
the database then it degrades to as though a key wasn't in use.  That
is, a personalization key is sometimes better, never worse.

But, without password salting a personalization key isn't as effective
due specifically to Marsh's point C.

Brandon

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