Subject: RE: [rohc] Comments on sigcomp-extended-02

From: "Price, Richard" <[email-masked]>
Date: Thu, 14 Mar 2002 16:12:18 -0000

> Hi Zhigang and others,
> 
> I really fancy the following suggestion you have in your posting:
> 
> ''However, I think we can add STATE_FREE(%id_start, 
> %id_length) to the base draft as suggested by Adam during 
> offline discussion two weeks ago. It allows the compressor to 
> explicitly delete a state on the decompressor side. Security 
> issue has been discussed and to my understanding there is no 
> new risk. ''
> 
> 
> In fact, a similar idea was raised in 
> http://www.cdt.luth.se/rohc/msg03652.html, but at the time it 
> seemed to be impossible due to security considerations. 
> 
> Are there any new facts of what can be done from the security 
> perspective?
> 
> In any case, if this is allowed i think we should definitely 
> include it in the draft.

Hi Jan,

Security in the SigComp-05 draft has been enhanced in order to
correctly support announcement information. When a state creation
and/or announcement request is made the application returns
more than just a simple "yes/no" to the request; in fact if the
request is successful then it provides the identity of the sending
endpoint as well. This is necessary so that SigComp knows which
compressor must be supplied with the announcement information.

As a bonus, since the application supplies the identity of the
endpoint which made the state creation request, SigComp can keep
track of the states created by each endpoint. This means that it
can remember the states created by the endpoint and can delete them
when the endpoint needs to free up some state memory.

Currently the base draft just deletes state using a FIFO algorithm,
but having an explicit STATE-FREE instruction would be even better
provided that there are no IPR issues. I believe that SigComp-05
prevents this from adding new security risks. The reason for this
is that STATE-FREE is only a request to delete state rather than
an explicit command; the actual state deletion can only be carried
out with the permission of the application.

Regards,

Richard

---

From: "Dr. Carsten Bormann" <[email-masked]>
Date: Thu, 14 Mar 2002 18:03:02 +0100

> The reason for this

Actually, STATE-FREE is an advisory that the state will no longer be used by
this endpoint.
There may be other endpoints using the same state.  State can only be
deleted once there is no endpoint referencing it any more.
STATE-FREE cannot have an effect unless the endpoint issuing it is
identified securely.
(Minor nit.)

Gruesse, Carsten

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