Subject: [Sip-security] Second part of minutes from SIP Security Adhoc at 51st IETF

From: "Frank W. Miller" <[email-masked]>
Date: Mon, 13 Aug 2001 14:34:24 -0400

This set was taken by Charles Kalmenek…

Frank W. Miller, Ph.D.
Chief Technical Officer
sentitO Networks, Inc.
www.sentito.com

SIP Security Ad-hoc, Wednesday evening
 
Start with threat model.  Start with Mike?s draft.  
 
Hop by hop vs. end to end is different from inside vs. outside.   Inside
means participants in the call itself; keeping outsiders out is easier;
may degenerate into hop by hop security.  
 
If your threat is an outsider, may be better using a hop by hop model
rather than http digest. Is the cost of these other methods
significantly higher?
 
Threats
 
Identical message replay
Modified message replay
Message forgery (e.g., impersonation)
Disclosure of signaling information
Denial of service (message injection, message deletion)
 
Theft of service (e.g., through replay attack of intercepted signaling)
Hang up somebody?s call
Bill diversion
Registration hijacking
User identity masquerading/spoofing
Impersonate another user
Impersonate a proxy
Create a registration that shouldn?t exist
Resource consumption (e.g., creation of state)
 
Authentication
Authorization
Confidentiality
Integrity
 
Pyramid picture can be used for analyzing trust boundaries
 
               P-bg
             /      \
        P-a     P-b
       /               \
 UAa ----------- Uab
 
This doesn?t help you understand which mechanisms are needed; it?s
useful to know when to invoke a particular mechanism.  
 
Henning: how do we convey desires and requirements for security along
the way?
 
End-to-end body confidentiality is needed, since bodies may be used to
carry end-to-end keys.
 
Mike: Parties along the path need to be able to authenticate UAC.
Henning: No, I don?t care that someone unknown to me makes a call to me.
It is useful to know it came from the Gas & Electric company.  Brian: Do
we need to be able to authenticate domains?  Chuck: similar to behavior
of caller id from PBXs where general number is provided as caller id.
 
Relationship between anonymity, authenticity and privacy.
 
Brian wants to have a simple hop by hop security mechanism (e.g., TLS)
in the bis document, and not much else.  
 
EAP authentication is being proposed for 3GPP.
 
Henning would like to use TLS; Mike would like to IPSec.  Mike?s concern
about TLS is that it doesn?t work with UDP.  Henning: TCP may not be so
bad for signaling trunks.  Dave: but you get HOL blocking.  Henning: you
are likely to have trust relationships with entities that you
communicate with a lot.  Brian: this is not a reason for distinguishing
between IPSec and TLS.
 
Problems with IPSec: keying is harder to do automatically;  because it?s
built into the OS, you end up assuming that  because a message came from
a particular IP address, you should trust it. Henning: we don?t need to
make this an either-or choice.   Dave: UA-proxy and proxy-proxy may be
different.  UA?s are currently not required to implement TCP.   Brian:
IPSec is not in any OS but SunOS.  Need to pick one that is mandatory to
implement.  There is no mandatory to use requirement.