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

[Dean Willis <[e-mail]>]

On Feb 28, 2008, at 9:26 PM, Hadriel Kaplan wrote:

>
>
>> -----Original Message-----
>> From: [e-mail] [mailto:[e-mail]] On Behalf  
>> Of Eric
>> Rescorla
>> Sent: Thursday, February 28, 2008 2:14 PM
>>
>>> 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.
>
> Not to belabor this topic, but I don't think retargeting is an issue  
> for SIP use of IBE, if by that you mean Alice sent a request to Bob  
> and it got retargeted to Charles and thus Charles could not decrypt  
> it.  It would be considered a feature to some folks.  It would take  
> a second request to fix it, but that's only if retargeting occurs,  
> and then the caller gets to decide if they want to do it to Charles.
>
> The real killer for SIP usage of IBE is that Alice has no idea what  
> KG group Bob is a member of a priori.  For example if Alice is a  
> member of a KG group called "CLINTON", and Bob is a member of KG  
> group "OBAMA".  Alice won't know ahead of time that Bob is a member  
> of OBAMA.  Even if Alice had the OBAMA keying info at hand to use,  
> she wouldn't know Bob is a member of it until she tries reaching  
> Bob.  Since that would happen a lot, there's no serious advantage  
> over conventional pub-key retrieval to encrypt, methinks.

But if both the "CLINTON" and "OBAMA" groups were both subsidiaries of  
the "DEMOCRAT" group, hierarchical inheritance takes care of the  
problem.

You can also do some things using DNS or the like to figure out which  
"group" an identity is in if you can't deduce from the domain.

But where it really shines is in bounded user groups -- say, the set  
of participants in Skype, or people in the Department of Defense, or  
employees of Walmart, when the communication is WITHIN that group.

And if we're talking about something like a single P2PSIP overlay or  
confederation of overlays, then group closure is easy.

The larger the group and the more relatively frequent communications  
are within that group, the greater the efficiency gain from IB crypto.

--
Dean

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