[Security] Enhancements to H.233 and H.234

Tue Sep 17 06:48:48 EDT 2002

Roni,

regarding recommended DH parameters, H.234 apparently follows a different
philosophy than H.235:

H.234 does not recommend any particular DH set. Any DH-set should work as
long as the parameters are chosen with care.
On the other hand, H.235 recommends certain sets of DH parameters (taken
from RFC2412). H.235 also allows to use arbitrary (i.e. non standardized)
DH-parameters if there is a need for.

Now I do not know why H.234 did not recommend any particular set. I can only
speculate: perhaps it was decided to leave that issue to the implementation.
Or such agreed parameters were simply not available in those former days.
Anyway, this makes the ITU recommendation pretty vague and introduces
potential interoperability problems.

H.235 defines the recommended DH-values in order to yield a consistent
security level among key management and media security taking into account
the media encryption algorithms and also exportability issues. It was
further recognized that using the well-defined DH parameter aids in
interoperability and simplifies implementations.

One good question that we are touching is:
Should we leave H.234 in the same spirit as the document is/was?
Or should we improve and add more recommendations such as suggested
DH-parameters and some more text?

I can see arguments for either way...

With kind regards

Martin Euchner.
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 -----Original Message-----
From:   Even, Roni [mailto:roni.even at POLYCOM.CO.IL]
Sent:   Tuesday, September 17, 2002 8:11 AM
To:     ITU-SG16 at echo.jf.INTEL.COM
Subject:        Re: [Security] Enhancements to H.233 and H.234

Patrick,
I still do not understand number 1 since this tag is in the context of h.233
and should be specified like that.
As for the prime number look at the RFC 2412. H.235 refer to it since it
includes verified prime numbers for 1024 and 1536 and I suggest we have the
same recommendation as H.235. Maybe you should consult with Martin Euchner
Regards
Roni

> -----Original Message-----
> From: Patrick Luthi [mailto:patrick.luthi at tandberg.no]
> Sent: Tuesday, September 17, 2002 12:59 AM
> To: Even, Roni; ITU-SG16 at echo.jf.INTEL.COM
> Subject: RE: [Security] Enhancements to H.233 and H.234
>
>
> Roni,
>
> See my answers in-line!
>
> Regards,
>
> Patrick
>
> At 16:03 9/12/2002 +0300, Even, Roni wrote:
> >Patrick,
> >I looked at the contributions and have some comments.
> >
> >1. In H.233 why the new tag class, why don't you use 11 as
> the rest of H.233
> >messages.
>
> We used 00 because it defines the universal tag class (11
> being context
> specific), and we thought that SE_NULL, as data type null
> message, would
> best belong to that class. This makes it consistent with ASN.1.
>
> >2. By adding the new encryption algorithm you need a longer
> DH prime. In
> >H.235 they have a table in annex D which is based on
> RFC2412. Do you think
> >we should have the option to recommend the same numbers as
> H.235 does.
>
> H.233 nor H.234 are specifying any Diffie Hellman prime values and my
> understanding is that it is left to the implementor to choose
> the best
> value. I see your point, and in the interest of interoperability, a
> specified value would help.
> I will think about how to best integrate some text specifying
> prime values
> in H.234. One idea was to add a note in the section about
> Diffie Hellman
> (clause 4/H.234) saying something (inspired by D.7.1/H.235) like this:
> It is recommended to use a prime value of 512 bits for the
> DES algorithm
> (when exportable security is of concern), 1024 bits for
> Triple DES and AES
> algorithms (when high security is of concern), and 1536 bits
> for Triple DES
> and AES algorithms (when very high security is of concern).
> Would that address your concerns? Any feedback or comments
> are welcomed!
>
>
> >Regards
> >Roni Even
> >
> > > -----Original Message-----
> > > From: Patrick Luthi [mailto:patrick.luthi at TANDBERG.NO]
> > > Sent: Friday, August 30, 2002 1:54 AM
> > > To: ITU-SG16 at echo.jf.INTEL.COM
> > > Subject: [Security] Enhancements to H.233 and H.234
> > >
> > >
> > > Dear experts,
> > >
> > > We would like to share with you 2 proposals for enhancements
> > > to H.233 and
> > > H.234 that we are planning to submit to the October
> meeting of SG16.
> > >
> > > Enhancements to H.233: this contribution proposes to add the
> > > Triple Data
> > > Encryption Algorithm (TDEA or triple DES) and the
> Advanced Encryption
> > > Standard (AES) to the list of algorithms in H.233 along with
> > > corrections of
> > > some inconsistencies.
> > >
> > > Enhancements to H.234: this contribution proposes changes to
> > > H.234 to allow
> > > the exchange of asymmetric length of encryption keys.
> > >
> > > Please let me know if you have any suggestions or comments!
> > > The plan would
> > > be to ask for Consent for both recommendations at the
> closing of the
> > > upcoming SG16.
> > >
> > > Best regards,
> > >
> > > Patrick
> > >
> > > _____________________________
> > > Patrick Luthi
> > > Manager - Technical Standards
> > > Rapporteur (chairman) for the ITU-T multimedia systems,
> terminals and
> > > data-conferencing Experts group (Question 1/16)
> > > TANDBERG
> > > N-1366 Lysaker, Norway
> > > Phone: + 47 67 125 125
> > > e-mail: patrick.luthi at tandberg.no
> > >
>

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