[999] in Kerberos
Why is initial user authentication done the way it is?
daemon@ATHENA.MIT.EDU (Jonathan I. Kamens)
Thu Jun 14 17:49:32 1990
Date: Thu, 14 Jun 90 14:29:39 -0400
From: "Jonathan I. Kamens" <jik@pit-manager.MIT.EDU>
To: mdl@B.GP.CS.CMU.EDU
Cc: kerberos@ATHENA.MIT.EDU
In-Reply-To: Mark Lillibridge's message of Thu, 14 Jun 90 11:06:42 EDT <9006141634.AA20691@PIT-MANAGER.MIT.EDU>
From: Mark Lillibridge <mdl@B.GP.CS.CMU.EDU>
Date: Thu, 14 Jun 90 11:06:42 EDT
The short answer: Because this scenario is also vulnerable to a
dictionary attack. Suppose I wanted to break your password under the
new scheme. I just wait until you log in, recording your data request
in part 1. I now pretend to be Kerberos, and try and decrypt your
initial request with each possible key until I succeed. Once I have a
key that successfully decodes your request, I have found your key.
This assumes that you have the ability to monitor transactions going
over the network. The way things stands now, you do not need to be
able to do this in order to get an encrypted packet to hack on,
whereas in the proposed system I described, you do; therefore, my
system provides at least some level of increased security.
Incidentally, it seems to me that the way the Kerberos protocol is
currently written, Kerberos is even *more* vulnerable to dictionary
attack than is /etc/passwd encryption.
This is because there are no seeds involved, so it's possible to
build up a large database of encrypted keys, because the decryption is
faster than crypt() (or at least I think it is; I'm not really sure
about this one, so someone correct me if I'm wrong), and because it's
possible to request an encrypted tgt for anyone in any realm, thus
eliminating the security (albeit slight) of passwd files not being
available for cracking on.
Given all this, it would seem to me that the issue of making the
protocol more secure should have been a high priority in the Kerberos
V5 design. Is there a particular reason why it wasn't?
Jonathan Kamens USnail:
MIT Project Athena 11 Ashford Terrace
jik@Athena.MIT.EDU Allston, MA 02134
Office: 617-253-8495 Home: 617-782-0710
