Subject: RE: [Isms] Discussion: Architecture direction for ISMS

From: "Blumenthal, Uri" <[email-masked]>
Date: Mon, 18 Apr 2005 17:13:18 -0400

Blumenthal> I was saying that CURRENTLY *by conscious design*
    Blumenthal> SNMP entities do not have credentials of its own, and
    Blumenthal> operate exclusively on behalf of users who request
    Blumenthal> operations.

> Is the following a technically accurate restatement of the above:
>
> Currently, by design, USM SNMP engines share a credential for each
> user?

IMHO no it is not. Because user credentials kept by one SNMP engine *at
least* cryptographically differ from credentials of the same user on a
different SNMP engine. So there is no sharing.

It is possible though that user credentials for each SNMP engine (for
one user) are generated from one source (user password). In that case
the stored credentials will still be different (grabbing keys from one
engine doesn't open the doors to another), but a way to attack is clear:
brute-force through the password space (the weakest link).

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From: Sam Hartman <[email-masked]>
Date: Mon, 18 Apr 2005 21:02:15 -0400

>>>>> "Blumenthal," == Blumenthal, Uri <[email-masked]> writes:

    Blumenthal> I was saying that CURRENTLY *by conscious design* SNMP
    Blumenthal> entities do not have credentials of its own, and
    Blumenthal> operate exclusively on behalf of users who request
    Blumenthal> operations.

    >> Currently, by design, USM SNMP engines share a credential for
    >> each user?

    Blumenthal,> IMHO no it is not. Because user credentials kept by
    Blumenthal,> one SNMP engine *at least* cryptographically differ
    Blumenthal,> from credentials of the same user on a different SNMP
    Blumenthal,> engine. So there is no sharing.

OK.  I will push the spec up on my reading list.  I'm horribly
confused here.

---

From: Wes Hardaker <[email-masked]>
Date: Mon, 18 Apr 2005 18:13:28 -0700

>>>>> On Mon, 18 Apr 2005 21:02:15 -0400, Sam Hartman <[email-masked]> said:

Sam> Currently, by design, USM SNMP engines share a credential for
Sam> each user?

Sam> OK.  I will push the spec up on my reading list.  I'm horribly
Sam> confused here.

No, you're both right but you're missing what each other is saying (I
think).

    B
   /
  / 
A
 \
  \
   C

In the above 3 engines, A B and C, there may be one USM user name
"Sam" known to all three.  If A is the command generator then the key
that it shares with B for "Sam" (potentially, but not required to be,
derived based on the EngineID) will be different than that it shares
with C (a unique combination of user name and engineID distinctly
identifies a USM user).

Sam's point, I think, is that a credential is actually shared between
A and B and that thus both engines do, at time of communication, have
information about the shared user credential.  B won't respond unless
A has properly proven the credential is shared, and A won't accept a
response from B if the credential is not identical to the request it
sent out (assuming at least authNoPriv here).

Uri's point is that the credential shared for "Sam" between A and B is
different than that for the credential which is shared between A and C
since the credential between A and B is unique to B's engineID (A = CG
here still) and between A and C is unique to C's engineID.

-- 
Wes Hardaker
Sparta, Inc.

---

From: Sam Hartman <[email-masked]>
Date: Mon, 18 Apr 2005 21:47:57 -0400

>>>>> "Wes" == Wes Hardaker <[email-masked]> writes:

    Wes> Sam's point, I think, is that a credential is actually shared
    Wes> between A and B and that thus both engines do, at time of
    Wes> communication, have information about the shared user
    Wes> credential.  B won't respond unless A has properly proven the
    Wes> credential is shared, and A won't accept a response from B if
    Wes> the credential is not identical to the request it sent out
    Wes> (assuming at least authNoPriv here).

Yes, that was my point.

    Wes> Uri's point is that the credential shared for "Sam" between A
    Wes> and B is different than that for the credential which is
    Wes> shared between A and C since the credential between A and B
    Wes> is unique to B's engineID (A = CG here still) and between A
    Wes> and C is unique to C's engineID.

OK, understood.