Re: [Sip] comments on draft-kupwade-sip-iba-00

[Michael Thomas <mat at cisco.com>]

Eric Rescorla wrote:
> At Thu, 28 Feb 2008 12:46:21 -0600,
> Dean Willis wrote:
>   
>>
>> A global or semi-global KG makes excellent sense in large domains,
>> especially where there are significant resource constraints.
>>     

Are we talking about a trust anchor that isn't DNS and isn't shipped in
web browsers currently?
>> Consider, for example, the 3GPP world of GSM phones. A KG hierarchy
>> rooted at the GSMA with each operator then having a subordinate KG could
>> make a lot of sense. We could get end-to-end security with significantly
>> fewer bits being transmitted than if users had to send copies of their
>> certificates along with every message.
>>
>> Similar characteristics apply in peer-to-peer cases. The enrollment
>> process could include a KG interaction. The resulting identity could be
>> used with IBS for node identification in the overlay as well as message
>> source verification ("identity" in and RFC 4474 context). This helps
>> prevent a number of the easy attacks on P2P infrastructure.
>>     
>
> Yes, and this is all equally possible with PKI systems. As I
> said at the beginning, the only thing that IBS is bringing
> to the party here is a smaller credential. As far as I'm
> awre, the size of the cert is not the primary reason for lack
> of adoption of any of these schemes 
>
> Again, what does IBS bring to the party except compression? [0].
>   

I just read through this too and I saw that in the abstract, and
also thought the size of credentials might be  "a problem" but isn't
"THE PROBLEM" with deployment.

Reading (quickly) through draft, I didn't get a sense for what
other problems this solves if any. I'll mention that in addition to
compression you can also use other methods to make key/name
bindings too which don't rely on krufty ASN.1 blobs to make
the point.
>   
>> And of
>> course, IBE could provide for message privacy as well as integrity
>> across the untrusted peers that will be serving as proxies.
>>     
>
> And now we're talking about something totally different: IBE.
> I agree that IBE has significantly different characteristics from
> PKI. The problems with IBE in SIP are totally different: namely
> not knowing the actual identity of the recipietn of the message.
> This is the norm in both SIP (retargeting) and P2P (churn)
> systems.
>   

So there's no majick here seemingly. Darn.

       Mike
> -Ekr
>
> [0] It's worth noting that the combination of using ECC and 
> doing LZW on certificates would significantly shrink the
> size of the cert. I haven't done the math, but I suspect down
> to the point where it's not the dominant factor.
>
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>   

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