RE: IPS-All: Reminder - Security draft last call ends Monday, Jul y 1 at 8am EST

[Black_David@emc.com]

Excerpting the important point:

> o.k. Lets see what I have understand now: If PFS by rekeying is not
> mandatory to use (and this is the situation) then you can established with
> DH exchange a key (referred here now by me as long-term key) and use other
> protocols, e.g. Basic Quick Mode or Stealthkey, to derive multiple keys
> (referred here as short-term keys) from the long-term key.  The compromise
> of short-term keys must not compromise the long-term key. This formulation
> should be also conform with Paul Koning's comment. 

Yes, with a slight clarification of "must not" - "when properly used,
compromise of short-term keys must not compromise the long-term
key".  Eventually, any key is vulnerable to compromise from overuse,
even if that use is only as part of generation of other keys.

Thanks,
--David
---------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 249-6449 *NEW*      FAX: +1 (508) 497-8500
black_david@emc.com         Cell: +1 (978) 394-7754
---------------------------------------------------

> -----Original Message-----
> From: Christina Helbig [mailto:cbh@zyfer.com]
> Sent: Friday, June 28, 2002 7:37 PM
> To: 'Black_David@emc.com'; ips@ece.cmu.edu
> Subject: RE: IPS-All: Reminder - Security draft last call ends Monday,
> Jul y 1 at 8am EST
> 
> 
> David, thank you for the time for answer. Comments inside:
> 
> > -----Original Message-----
> > From: Black_David@emc.com [mailto:Black_David@emc.com]
> > Sent: Friday, June 28, 2002 1:07 PM
> > To: Christina Helbig; ips@ece.cmu.edu
> > Subject: RE: IPS-All: Reminder - Security draft last call 
> ends Monday,
> > Jul y 1 at 8am EST
> > 
> > 
> > Christina,
> > 
> > Thanks for your comments.  I don't think there are technical issues
> > in the two areas of concern you've raised - could you please check
> > the following discussion and see if it's ok?
> > 
> > I. Rekeying and PFS
> > 
> > The requirement for PFS is "MUST implement" (must support) 
> > not "MUST use".
> > Christina's text appears to be objecting to a "MUST use" 
> > requirement - if
> > so, this is not a problem, as the requirement is "MUST implement",
> > which is the intention of the "must support" wording in 
> section 2.1 of
> > the security draft.
> o.k. I understood.
> > 
> > II.  Manual keying and PFS
> > 
> > Section 5.9 was not intended to provide an exception to the 
> > "MUST NOT use"
> > manual keying requirement stated in Section 2.3.3.  The 
> > Section 5.9 text
> > should be clarified to make this clear.
> > 
> o.k.
> > > Second, if PFS would be not mandatory by rekeying then you 
> > can use manual
> > > keying together with other protocols for frequent 
> rekeying, e.g. our
> > > proposal.
> > 
> > I don't think there's an issue here, but some terminology 
> > clarification is
> > in order - in essence properly designed "manual keying together with
> > other protocols for frequent rekeying" is "preshared keying" and is
> > allowed (in fact it's required).
> > 
> > The term "manual keying" describes situations in which keys are
> > preconfigured
> > (manually) and then those keys are used as the session keying 
> > material for
> > the SAs that carry traffic - rekeying is accomplished by (manually)
> > configuring new keys.  Manual keying is forbidden (MUST NOT use) for
> > IP Storage due to the inability to automatically generate new secure
> > session keys.
> > 
> > The term "preshared keying" describes situations in which the 
> > preconfigured
> > keys are used to derive multiple session keys in a fashion 
> > that compromise
> > of a session key does not imply compromise or serious 
> weakening of the
> > preconfigured keys (IKE uses a keyed prf [usually a hash] to 
> > obtain this
> > property).  Pre-shared keying is REQUIRED (MUST implement).
> > 
> o.k. Lets see what I have understand now: If PFS by rekeying is not
> mandatory to use (and this is the situation) then you can 
> established with
> DH exchange a key (referred here now by me as long-term key) 
> and use other
> protocols, e.g. Basic Quick Mode or Stealthkey, to derive 
> multiple keys
> (referred here as short-term keys) from the long-term key . 
> The compromise
> of short-term keys must not compromise the long-term key. 
> This formulation
> should be also conform with Paul Koenigs comment. 
> > The StealthKey mechanism described in 
> > draft-helbig-stealthkey-01.txt is
> > a preshared keying mechanism that can automatically generate new
> > (short-term) session keys, and hence is not forbidden by the 
> > requirement
> > that manual keying MUST NOT be used.  OTOH, StealthKey is not 
> > specified
> > in any of the IP Storage protocol drafts.
> > 
> o.k. We try to get some attention from the IPSec working 
> group for this
> proposal. I think this is the right WG. I was only concerned 
> that we have no
> chance to use this for IP Storage protocols but the right 
> understanding of
> Internet-Standards is really a skill after long-training.
> Thank you 
> Christina
> > Thanks,
> > --David
> > ---------------------------------------------------
> > David L. Black, Senior Technologist
> > EMC Corporation, 42 South St., Hopkinton, MA  01748
> > +1 (508) 249-6449 *NEW*      FAX: +1 (508) 497-8500
> > black_david@emc.com         Cell: +1 (978) 394-7754
> > ---------------------------------------------------
> > 
> > > -----Original Message-----
> > > From: Christina Helbig [mailto:cbh@zyfer.com]
> > > Sent: Friday, June 28, 2002 2:03 PM
> > > To: 'Elizabeth Rodriguez'; ips@ece.cmu.edu
> > > Subject: RE: IPS-All: Reminder - Security draft last call 
> > ends Monday,
> > > Jul y 1 at 8am EST
> > > 
> > > 
> > > These are my IPS Security draft last call comments. I'm also 
> > > impressed about
> > > the good work others have done.
> > > 
> > > I have problems with following text about rekeying and 
> > manual keying. 
> > > 
> > > I. Rekeying and PFS:
> > > 
> > > First there are two statements, which I think are not consistent:
> > > 
> > > a) 2.1.  Security requirements
> > > ...The IP block storage security protocols must support perfect
> > > forward secrecy in the rekeying process.
> > > 
> > > b) 2.2.  Resource constraints
> > > Computational horsepower should be available to perform a 
> > > reasonable amount
> > > of exponentiation as part of authentication and key derivation for
> > > connection setup.  The same is true of rekeying, although the
> > > ability to avoid exponentiation for rekeying may be desirable (but
> > > is not an absolute requirement).
> > > 
> > > In RFC 2409 is a clear definition of PFS for IKE:
> > > 3.3 Perfect Forward Secrecy 
> > > When used in the memo Perfect Forward Secrecy (PFS) refers to 
> > > the notion
> > > that compromise of a single key will permit access to only 
> > > data protected by
> > > a single key. For PFS to exist the key used to protect 
> > > transmission of data
> > > MUST NOT be used to derive any additional keys, and if the 
> > key used to
> > > protect transmission of data was derived from some other 
> > > keying material,
> > > that material MUST NOT be used to derive any more keys. 
> > > 
> > > If a) is the requirement than you can never avoid 
> exponentiation for
> > > rekeying because otherwise you must use keying material to 
> > > derive more than
> > > one key.
> > > 
> > > Second I think PFS should not be a requirement for rekeying, 
> > > only a nice to
> > > have. Why?
> > > 
> > > There is currently a discussion about PFS and rekeying by SOI 
> > > in the IPSec
> > > list and here is what I wrote and nobody opposed me (what not 
> > > mean that I'm
> > > right ;-)
> > > 
> > > "IMO there is a mix of the issue of PFS and rekeying in the 
> > > discussion.
> > > 1. Rekeying is needed if the amount of with the same key 
> > > encrypted data goes
> > > beyond specific values, because of some passive attacks 
> against the
> > > encrypted data (dependable also of the encryption algorithm 
> > > and its mode)
> > > and the active attack of replaying by ESP after the sequence 
> > > number counter
> > > has started again.
> > > 2. The need for PFS by the process of rekeying is not based 
> > > on protection
> > > against this attacks under 1. 
> > > 3. The property of PFS is an advantage in the case of 
> > > unauthorized access to
> > > secret information used to generate the communication keys. 
> > > If this secret
> > > information can be secured against unauthorized access then 
> > > rekeying can be
> > > done without the property of PFS. 
> > > 4. On the other hand there is always a need by IKE to 
> protect secret
> > > information against unauthorized access used for phase 1 
> > > authentication. If
> > > the protection of this secret information in the system is 
> > > sufficient why
> > > should there the protection of another secret information be 
> > > insufficient?
> > > 
> > > My proposal is: Rekeying is necessary under specific 
> > > circumstances, which
> > > should be described. PFS is not needed if the secret 
> > > information used to
> > > generate different communication keys is protected against 
> > > unauthorized
> > > access in the same manner like the phase 1 authentication secret."
> > > 
> > > The main reason for avoiding mandatory PFS by rekeying, I 
> > think is the
> > > computational overhead. I have mentioned in the SOI discussion:
> > > 
> > > "I found different statements about the CPU time necessary for one
> > > exponentiation between 30ms and some seconds. In the
> > > draft-ietf-ips-security-13.txt it's time for rekeying for one 
> > > SA by 10Gbps
> > > and 3DES in CBC mode all 27.5s or before 2^35 bytes are sent. 
> > > Assume the
> > > case of some hundred SAs per peer with permanently 
> > > irregularly distributed
> > > traffic between the SAs. Then rekeying at time is necessary 
> > > for every SA all
> > > 27.5 s. This looks like a computational border, so you must have
> > > amount-based rekeying in this case and encrypted bytes or 
> > > blocks must be
> > > counted for every SA. Is that a computational border too?"
> > > 
> > > There was no answer like "This is no problem". 
> > > 
> > > Last I like to mention the possibility to rekey without 
> > exchanges (and
> > > without PFS). We have developed a protocol for frequent 
> > > rekeying without
> > > exchanges and would be happy if some folks could have a look 
> > > at this and say
> > > if it makes sense or not
> > > (<http://www.rfc-editor.org/internet-drafts/draft-helbig-steal
> > thkey-01.txt>)
> >  
> > II. Manual keying and PFS:
> > 
> > First there are again two statements, which I think are not 
> > consistent:
> > 
> > 
> > c) 2.3.3. IKE
> > ...Manual keying MUST NOT be used since it does not provide 
> > the necessary
> > rekeying support.
> > 
> > d) 5.9 Use of AES in counter mode
> > 
> > ...The implication of this is that it is almost always an 
> error to use
> > IPsec manual keying with counter mode, except when the 
> implementation
> > takes heroic measures to maintain state across sessions.
> > 
> > That means there is an exception from MUST NOT?
> > 
> > Second, if PFS would be not mandatory by rekeying then you 
> > can use manual
> > keying together with other protocols for frequent rekeying, e.g. our
> > proposal.
> > Thank you for your patient regarding my bad English.
> > Christina
> > 
> > > -----Original Message-----
> > > From: Elizabeth Rodriguez 
[mailto:elizabeth.g.rodriguez@123mail.net]
> > Sent: Thursday, June 27, 2002 2:41 PM
> > To: ips@ece.cmu.edu
> > Cc: Elizabeth.G.Rodriguez@123mail.net
> > Subject: IPS-All: Reminder - Security draft last call ends 
> > Monday, July
> > 1 at 8am EST
> > 
> > 
> > Just a reminder to all to get your last call comments on the 
> > security draft in.
> > The cutoff is Monday July 1 at 8am EST
> >  
> > Thanks,
> >  
> > Elizabeth
> >  
> > 
>