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

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Date: Fri, 12 Dec 2014 01:21:32 +0000
From: Marsh Ray <maray@...rosoft.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: RE: [PHC] How important is salting really?

So the old security properties given by salting were:

A.      Prevents precomputation TMTO via rainbow tables

B.      Prevents attackers from re-using work on one hash against another

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

Today

(A)   may be still important

(B)   Is important to the extent that the attacker is not targeting a specific user.

(C)   Seems almost useless now.

-          Marsh

From: Ben Harris [mailto:ben@...rr.is]
Sent: Thursday, December 11, 2014 5:10 PM
To: discussions@...sword-hashing.net
Subject: Re: [PHC] How important is salting really?

"Dictionaries and candidate generation algorithms" are the main attacks precisely because we use salts. If nobody used salts the prevalent attack would still be rainbow tables.

On 12 December 2014 at 08:58, Bitweasil . <bitweasil@...ptohaze.com<mailto:bitweasil@...ptohaze.com>> wrote:

A factor of N slowdown in cracking, where N is the number of unique salts in the uncracked list of hashes.
On Dec 11, 2014 4:57 PM, "Marsh Ray" <maray@...rosoft.com<mailto:maray@...rosoft.com>> wrote:
Password security researchers learn more and more from data breaches seemingly every week. Dictionaries and candidate generation algorithms get better all the time. So here’s a question. Maybe the answer has changed over the last few years and we should revisit our assumptions.

Two different people independently choose this same password. It could be “ilovecats” or it could be something less obvious.

What is the probability that this password will not be in attackers’ dictionaries or it will be hard to crack?

(If this chance is small, then what do we gain by salting?)

-          Marsh

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