Re: [secdir] review of draft-ietf-sipcore-reinvite-06.txt

[Gonzalo Camarillo <[e-mail]>]

Hi Stephen,

did you have a chance to check whether my suggestions in the email below
address your concerns?

Thanks,

Gonzalo

On 27/10/2010 3:21 PM, Gonzalo Camarillo wrote:
> Hi Stephen,
> 
> thanks for your review. My answers inline:
> 
> On 21/10/2010 5:17 AM, Stephen Kent wrote:
>> I reviewed this document as part of the security directorate's 
>> ongoing effort to review all IETF documents being processed by the 
>> IESG.  These comments were written primarily for the benefit of the 
>> security area directors.  Document editors and WG chairs should treat 
>> these comments just like any other last call comments.
>>
>> This document (draft-ietf-sipcore-reinvite-06.txt) provides 
>> clarification on how to process a re-invite in SIP. The notion of a 
>> re-invite is defined in RFC 3261 (SIP). This document was created to 
>> clarify the description provided in 3261, based on feedback from 
>> implementers. It includes a number of examples designed to clarify. 
>> It is fair to say that this document not only offers clarifications, 
>> but also makes some changes to SIP handling of re-INVITEs. For 
>> example, the document notes that "Section 4.3 specifies new rules for 
>> the handling of target-refresh requests."
>>
>> The document makes reference to "properly" authenticated requests in 
>> a couple of places (4.4 & 4.6), but provides no indication of what 
>> constitutes proper authentication. I think it would be appropriate to 
>> include references to whatever SIP security mechanisms are currently 
>> recommended for message/session authentication (as opposed to what 
>> 3261 said 8 years ago).
> 
> I suggest adding the following text in both places: "(see Section 26.2
> of RFC 3261)".
> 
> http://tools.ietf.org/html/rfc3261#section-26.2
> 
> The way user agents authenticate incoming requests has not changed much
> since RFC 3261 was published.
> 
>> The document has a trivial Security Considerations section:
>>
>>     This document does not introduce any new security issue.  It just
>>     clarifies how certain transactions should be handled in SIP.
>>     Security issues related to re-INVITEs and UPDATE requests are
>>     discussed in RFC 3261 [RFC3261] and RFC 3311 [RFC3311].
>>
>> I checked 3261 and I agree that this document provides a decent 
>> review of security for SIP in general, but it makes no specific 
>> mention of UPDATE or (re)INVITE messages and attendant security 
>> concerns. RFC 3311 has an almost trivial Security Considerations 
>> section, but at least it does specifically refer to UPDATE and 
>> (re-)Invite messages, briefly, and the need for authentication. I 
>> think it would be appropriate to add a discussion of how these 
>> clarifications operate in various SIP security contexts, e.g., use of 
>> TLS for point-to-point SIP security or use of S/MIME for end-to-end 
>> SIP security. A statement that the security offered for SIP when the 
>> initial call setup was processed cannot be undermined by a later 
>> re-INVITE or UPDATE would be reassuring (if accompanied by a 
>> rationale for that statement :).
>>
> 
> I suggest adding the following text to the Security Considerations
> Section. Feel free to edit the text if you wish:
> 
> "In particular, in order not to reduce the security level for a given
> session, re-INVITEs and UPDATE requests SHOULD be secured in a similar
> or stronger manner as the initial INVITE request that created the
> session. For example, if the initial INVITE request was end-to-end
> integrity protected or encrypted, subsequent re-INVITEs and UPDATE
> requests should also be so."
> 
> A discussion on which security mechanisms should be applied in different
> contexts in outside the scope of this document, IMHO. SIP has been and
> is being deployed in so different environments that we would need a
> whole document (or more likely a set of them) to discuss all relevant
> issues.
> 
> Thanks,
> 
> Gonzalo
> 
> 

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