Subject: AW: [Sipping] Via Hiding and integrity in 3GPP

From: Kroeselberg Dirk <[email-masked]>
Date: Fri, 12 Oct 2001 14:34:24 +0200

Hi,

maybe this helps to clarify things:
It seems that you are referring to an outdated version of 33.203 (possibly
v0.5.0)? The current version looks different, but anyway this is work in
progress.
As Miguel says, integrity protection is under discussion. The MITM attacks
you are concerned about are not possible, since integrity and (entity)
authentication are different building blocks that can terminate at different
entities in 3GPP. Authentication always runs between UA and the home
network.

There are related requirements in the security section of
draft-garcia-sipping-3gpp-reqs-00.txt. But nothing of this is linked to Via
Hiding.

Dirk

> -----Ursprüngliche Nachricht-----
> Von: James Undery [mailto:[email-masked]]
> Gesendet am: Freitag, 12. Oktober 2001 13:28
> An: Miguel A. Garcia
> Cc: [email-masked]
> Betreff: [Sipping] Via Hiding and integrity in 3GPP
> 
> Hi,
> 
> All these discussions about Via Hiding scare me from a security stand
> point. Please correct me if I am wrong, but, Via Hiding is mainly for
> commercial reasons (i.e. hiding info from competitors). (If not it's
> security through obscurity which is acknowledged as a bad practise.)
> This Via-Hiding must occur on the all the P-CSCFs and I-CSCFs (incase
> of reINVITEs). 3GPP TS 33.203 section 7.2.2 says "When the P-CSCF
> receives a SIP message, which is integrity, [sic] protected and the
> integrity check fails the P-CSCF shall silently discard that message".
> This implies to me integrity protection can never be enabled, opening
> the system to all manner of MITM attacks. If the integrity is hop by
> hop the authentication of the UA to its home network is going to be
> open to replay attacks (or include the original message exposing the
> info trying to be hidden).
> 
> James
> 
> 
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_______________________________________________
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---

From: "James Undery" <[email-masked]>
Date: Fri, 12 Oct 2001 14:10:43 +0100

> -----Original Message-----
> From: Kroeselberg Dirk [mailto:[email-masked]]

> v0.5.0)? The current version looks different, but anyway

I got the version from Miguel's draft.

> entities in 3GPP. Authentication always runs between UA and the home

Without having the authentication of the message tied to the content
of the message, authentication credentials can be replayed (or a
complex method such as time syncing is required). By separating
intergrity and authorisation you complicate or weaken the security,
complex security protocols are harder to trust, weak ones no better.
Simplifying the security model so these are different building blocks
makes it easier to satisfy the requirements, just doesn't cover the
way I'd attack a 3G network ;-)

> draft-garcia-sipping-3gpp-reqs-00.txt. But nothing of this

My experience of the security of Digest Authentication is what leads
me to believe info stripping and hiding are detrimental to secure
authentication.

James