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

[Eric Rescorla <ekr at networkresonance.com>]

At Tue, 26 Feb 2008 22:08:46 -0800,
Eric Rescorla wrote:
> 
> At Tue, 26 Feb 2008 23:55:22 -0600,
> Dean Willis wrote:
> > Here's a novel thing:
> > 
> > Let's say I know your identity is sip:ekr at networkresonance.com, and  
> > that your relationship with the PKG allows you to retrieve keys for  
> > parameterized versions of that identity.
> > 
> > I can construct a new cryptographic identity for you, perhaps "sip:ekr at networkresonance.com;ID=2009121222 
> > " and use that to sign a message to you. You've never seen this  
> > identity before and don't yet even have the private key for it. You  
> > then go to your PKG and retrieve said key and use it to verify the  
> > message.
> 
> Yes, this is a commonly discussed in the IBE world, but it doesn't
> work as well with store-and-forward signature systems because the
> relying party has no opportunity to insist that you provide an
> identity of his choice.

Oh, I should mention: what's the value of needing a new key to
*verify* the message? What does that do for the sender?
The relying party can simply assume the signature is valid.
If the sender wants to force the recipient to have a new 
key, they need to encipher the whole message or require
a signed receipt from the recipient.

-Ekr
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