Re: iSCSI: possible DH-CHAP rationale

["Ofer Biran" <BIRAN@il.ibm.com>]

David,

The problem with Assumption 1 (as David Jablon hinted) is that
obtaining a password can cause much more damage then a single
connection hijack.

And it might be more then just freely reusing it on that target.
I, for example, use the same password for all systems (shame
on me... but otherwise I'd be lost)- when the first system
complains on expiration I go into an overall renewal process.

Another related point - from iSCSI Security Considerations section:

"The CHAP authentication method (see Chapter 10) is vulnerable
to an off-line dictionary attack. In environments where this
attack is a concern, CHAP SHOULD NOT be used without additional
protection. Underlying IPsec encryption provides protection against
this attack."

So for DH-CHAP it would be fair to put the warning:

"The DH-CHAP authentication method (see Chapter 10) is vulnerable
to an impersonation combined with off-line dictionary attack.
In environments where this attack is a concern, DH-CHAP SHOULD NOT
be used without additional protection. Underlying IPsec
authentication provides protection against this attack."

If DH-CHAP is made the only MUST implement method, since IPsec is
not mandatory to use - such a MUST NOT use for the only MUST implement
method is a strange outcome.

  Regards,
   Ofer


Ofer Biran
Storage and Systems Technology
IBM Research Lab in Haifa
biran@il.ibm.com  972-4-8296253


Black_David@emc.com@ece.cmu.edu on 16/04/2002 00:39:33

Please respond to Black_David@emc.com

Sent by:    owner-ips@ece.cmu.edu


To:    ips@ece.cmu.edu
cc:
Subject:    iSCSI: possible DH-CHAP rationale



Reminder: This is NOT posted in my role as wg chair.

I thought I'd attempt to lay out a possible short
rationale for why DH-CHAP may be interesting:

(1) Assumption: If one is concerned about active attacks
 on session authentication, one should also be
 concerned about active attacks on the TCP session
 that       results after the authentication (e.g., TCP
 hijack for which exploit code is readily available).
(2) For iSCSI, the defense against active attacks
 on the TCP session after authentication is
 IPsec ESP.
(3) Hence, if one is concerned about active attacks,
 one should be running IPsec, and hence the
 scenario of concern for CHAP/DH-CHAP/SRP is
 passive attacks (e.g., packet sniffer).

DH-CHAP is clearly superior to CHAP in dealing with
passive attacks.  I don't think SRP is significantly
better in this regard.

Comments?
--David

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