[1397] in Kerberos
Verifying passwords without getting new tickets
daemon@ATHENA.MIT.EDU (Mark Lillibridge)
Mon May 20 19:52:24 1991
From: Mark Lillibridge <mdl@B.GP.CS.CMU.EDU>
Date: Mon, 20 May 91 17:28:05 EDT
To: cjr@simpact.COM
Cc: kctreima@eos.ncsu.edu, kerberos@ATHENA.MIT.EDU
In-Reply-To: Chris Riddick's message of Mon, 20 May 91 16:54:38 EDT <9105202054.aa04144@nss1.simpact.COM>
> From: Chris Riddick <cjr@simpact.COM>
>
> There is a way to render the dictionary attack ineffective. That is the use
> of one-time passwords. With a onetime password, even a TGT that was stolen
> simply by eavesdropping during login would not be useful. The password that
> was extracted via the dictionary attack (other other cryptanalysis) was only
> good for that login (i.e., TGT). The next time the user logs in, a
> different password will be required.
No. "One-time passwords" (this is really the wrong term for
this, but I know what you mean from the previous time you explained
yourself), do NOT by themselves render the dictionary attack
ineffective. If the user chooses his/her own master password, the fact
that one-time passwords are generated from it will not make the attack
impossible. [The details of how to alter the attack to deal with this
are left to the reader.]
However, forcing the user to use a randomly generated password
will render the dictionary attack useless. Granted, this is
particularly easy to do when the user already has to carry a one-time
password generator device around with him/her.
> From: "Jon A. Rochlis" <jon@MIT.EDU>
>
> All you need to do is eavesdrop on X logging in once.
>
>That is *much* harder than simply asking for a ticket in somebody
>else's name and therefore even though it's only a partial solution, it
>add significant value. Security is a world of tradeoffs.
>
> -- Jon
Jon's point above is important, however. Just because you can't
protect against the attack, doesn't mean you can't make it harder.
I don't remember off hand if krb5 actually prevents you from doing a
dictionary attack without eavesdropping or setting off alarms.
- Mark Lillibridge
