Re: Last Call: <draft-nandakumar-rtcweb-stun-uri-05.txt> (URI Scheme for Session Traversal Utilities for NAT (STUN) Protocol) to Proposed Standard

[Graham Klyne <[e-mail]>]

Hi Harald,

On 14/08/2013 19:49, Harald Alvestrand wrote:
> On 08/13/2013 12:14 AM, Graham Klyne wrote:
[...]
>> But, in a personal capacity, not as designated reviewer, I have to ask *why*
>> this needs to be a URI.  As far as I can tell, it is intended for use only in
>> very constrained environments, where there seems to be little value in having
>> an identifier that can appear in all the contexts where a URI may be recognized.
>>
>> The criteria for new URI schemes in http://tools.ietf.org/html/rfc4395 include:
>>
>> "New URI schemes SHOULD have clear utility to the broad Internet community,
>> beyond that available with already registered URI schemes."
>> -- http://tools.ietf.org/html/rfc4395#section-2.1
>>
>> This "utility to the broader community" is not clear to me, but I don't fully
>> understand the intended scope of this protocol, so I could be missing
>> something.  So, in declaring consensus for this specification, I would request
>> that this aspect at least be considered.
>
> I can only give  my personal opinion....
>
> 1) This is a format for a piece of data. This data cannot be expressed using any
> existing URI scheme - indeed, I don't think there exists another well-defined
> textual representation of this piece of data.
>
> 1) This is defining an identifier that will be used in W3C-defined APIs. W3C
> tends to use URIs every time they want a self-defining piece of data with a
> clearly defined structure.
> In the particular API where this is wanted, one wants to have STUN URIs, TURNS
> URIs and TURN URIs passed over the same interface. Thus, keeping with the W3C
> tradition of URIs seems reasonable.
>
> I think this answers the question about "utility to the broader community" to my
> satisfaction - your mileage may differ, of course.

Some thoughts occur to me:

1. My reading was that this is a generic NAT traversal protocol, so the 
requirement here is not Web/W3C specific.  But you do say "used in W3C-defined 
APIs"...

2. If this is being driven by W3C activities, this should probably be flagged 
with W3C TAG.  I'll raise it there.

3. URIs are not generally used as *data* formats, but rather as identifiers for 
resources.  Web architecture and REST principles tend to discourage information 
encoded in URIs in favour of data representation formats.  Cf. 
http://www.w3.org/TR/webarch/#uri-opacity, 
http://www.w3.org/2001/tag/doc/metaDataInURI-31.html

4. If the purpose here is simply to encode data, then there does already exist a 
suitable URI scheme, viz data:.  A new content type can be defined to actually 
encode the required data, and the whole be wrapped in a data: URI.  This 
approach has the advantage that alternative mechanisms (other than URIs) can be 
used to transfer the traversal data if required (though that may be moot in the 
very restricted intended scope of deployment for stun:, etc.)

>>
>> ...
>>
>> Further, according to http://tools.ietf.org/html/rfc5389 it appears that there
>> are security considerations with regard to the STUN protocol that it should
>> not be used in isolation:
>> [[
>>    Classic STUN also had a security vulnerability -- attackers could
>>    provide the client with incorrect mapped addresses under certain
>>    topologies and constraints, and this was fundamentally not solvable
>>    through any cryptographic means.  Though this problem remains with
>>    this specification, those attacks are now mitigated through the use
>>    of more complete solutions that make use of STUN.
>>
>>    For these reasons, this specification obsoletes RFC 3489, and instead
>>    describes STUN as a tool that is utilized as part of a complete NAT
>>    traversal solution.
>> ]]
>> -- http://tools.ietf.org/html/rfc5389#section-2
>>
>> It seems to me that creating a URI for STUN could encourage its use in
>> environments outside the "more complete solutions that make use of STUN".
>> This seems to be further reason that STUN[S] should not be a URI scheme.
>>
>> I have also suggested that, if registered, the URI scheme registration should
>> carries a "health warning" to this effect, and that it is not suitable for
>> general use that is not part of a "complete NAT traversal solution".  But I
>> also recognize that I do not fully grasp the security implications, and that
>> if those that do know better can agree that there is no potential for creating
>> security risks here, this suggestion may be unnecessary.
>
> This URI scheme does not represent STUN. It represents configuration data that
> is used to initialize a protocol machine that utilizes STUN.
>
> This configuration data has to be passed no matter what the format of the data
> is - whether it be URI or not.
>
> Thus, I do not think the argument raised is really relevant to the context. The
> data will be passed, and registering an URI scheme will cause no more and no
> less data to be passed.
>
> Again, my opinion.
>

If the URI is used only in very constrained contexts, then I agree.

But the whole point of using a URI is that, due to URI opacity, it can be used a 
a range of contexts where URIs are used.  If it cannot properly be used in those 
other contexts, I have to question if it really is a URI, as opposed to a string 
that happens to look like a URI.

I also note that this looks as if it may fall foul of the "confidential 
metadata" practice noted in the W3C TAG finding about metadata in URIs 
(http://www.w3.org/2001/tag/doc/metaDataInURI-31.html#hideforsecurity)

#g
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