e2e all the way (Re: Another entry in the internet security hall of shame....)

[Dave Howe]

Ian G wrote:
> Steven M. Bellovin wrote:
>> Really?  You know that the public key you're talking to corresponds to 
>> a private key held by the person to whom you're talking?  Or is there 
>> a MITM at Skype which uses a per-user key of its own?
> yes, this is the optimisation that makes Skype work,
> it is (probably) vulnerable to an MITM at the center.
Almost certainly though, the authorities of whatever government holds a VoIP hub 
are going to start insisting that traffic is interceptable at that hub. of 
course with SIP, unless you are proxying both ends, you are doing direct 
client-to-client links anyhow (so any crypto must be e2e, by definition); again 
however, unless there is some sort of PK retention in place, mitm attacks and 
attacks on the initial key negotiation are possible.

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