Re: DISCUSS:draft-ietf-sip-dtls-srtp-frameworkdraft-ietf-sip-dtls-srtp-framework

So maybe the draft should mention in section 8.1, second paragraph, also
the possibility that an attacker may only impersonate B, without doing a
full MITM-attack.

Peter

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On 
> Behalf Of ext Dean Willis
> Sent: Monday, November 10, 2008 6:03 AM
> To: Suresh Krishnan
> Cc: [email protected]; [email protected]; [email protected]; 
> [email protected]
> Subject: Re: [Sip] 
> DISCUSS:draft-ietf-sip-dtls-srtp-frameworkdraft-ietf-sip-dtls-
> srtp-framework
> 
> 
> On Nov 6, 2008, at 2:58 PM, Suresh Krishnan wrote:
> 
> > Hi Eric,
> >
> > Eric Rescorla wrote:
> >> But then the attacker isn't *intercepting* their communications.
> >> Alice calls Bob and ends up talking to someone but she knows
> >> that she doesn't know who. The point is you can't use this to
> >> mount an MITM attack.
> >
> > Again. I agree with what you said. What I was commenting on is the  
> > following text from the draft
> >
> > "Bob would know that an attack was happening.  The fact that
> > one side can detect this attack means that in most cases where Alice
> > and Bob both wish the communications to be encrypted there is not a
> > problem."
> >
> > My question was, how would Bob detect this attack?
> >
> 
> I think I understand the question. Let's check.
> 
> Bob is talking, but nobody hears what he says, since he's 
> encrypted it  
> for Alice but Alice isn't getting it. Bob may well notice 
> that there's  
> something strange here.
> 
> An attacker in this position could also have affected things 
> such that  
> the call never reaches Bob. His phone doesn't ring, and Bob isn't  
> talking to anybody. So how does he know there's an attack? Why would  
> Eve have even allowed any signaling to get to Bob in the first place  
> if she had this sort of control?
> 
> Bob can't detect the attack, and this is not an issue with 
> DTLS-SRTP;  
> it's a fundamental aspect of the signaling model.
> 
> However, Alice, who is the only party here that's honestly 
> engaged in  
> a call and saying something that could be intercepted, CAN 
> detect the  
> attack. That's the important piece.
> 
> 
> --
> Dean
> 
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