[VOIPSEC] Why a secure keyechange for media encryption?

[Michael Prochaska]

Gupta, Sachin schrieb:
> Even with PKI, how you do the key exchange with the other end. As I
> mentioned before, the location of the one end is not known to other end.
> In most of the cases it will only be known to some Registrar(or some
> other sip entity). So PKI can not be used between 2 end points in this
> situation (which will mostly be the case).

sorry, but i don't understand your doubt.

of course, if i call foo at bar.com i don't know where foo at bar.com is. but 
as you say, there must be a registrar at bar.com which knows where 
foo at bar.com is.

to get the public key of foo at bar.com there has to be a service at 
bar.com which provides you with the key.

are there any problems i don't see?

regards,
michael

> Sachin
> 
> -----Original Message-----
> From: Michael Prochaska [mailto:tm021090 at fh-stpoelten.ac.at] 
> Sent: Friday, April 28, 2006 1:49 PM
> To: Gupta, Sachin
> Cc: voipsec at voipsa.org
> Subject: Re: [VOIPSEC] Why a secure keyechange for media encryption?
> 
> Gupta, Sachin schrieb:
> 
>>I am wondering how do you exchange the keys for encrypting the SDP 
>>end-to-end. Most of the time you do not even have the location 
>>information of the other end. How would key exchange work then?
>>One solution would be the pre-shared keys, which is not scalable.
> 
> 
> that is the main focus of my thesis :-) .... the key exchange problem
> 
> i think the only acceptable way will be any form of a PKI.
> TLS is fine but without certificates it's vulnareable for MITM.
> 
> in my mind there must be PKI clouds (providers, big companies - cross
> certification) to assure  real secure communication.
> 
> i have interpreted the "good luck with that" as general problems with
> S/MIME in connection with SIP.
> 
> regards,
> michael
> 
> 
> 
>>Sachin
>>
>>-----Original Message-----
>>From: Voipsec-bounces at voipsa.org [mailto:Voipsec-bounces at voipsa.org] 
>>On Behalf Of Michael Prochaska
>>Sent: Friday, April 28, 2006 12:51 PM
>>To: Hadriel Kaplan
>>Cc: voipsec at voipsa.org
>>Subject: Re: [VOIPSEC] Why a secure keyechange for media encryption?
>>
>>
>>
>>>If you don't trust the hop-by-hop signaling path to remain secure, 
>>>don't use it - your signaling is almost as sensitive as your media - 
>>>more for some, less for others.
>>
>>
>>that's the point in my eyes too. i would even say the signaling is 
>>more sensitive than the media. the media may be sensitive sometimes 
>>but the signaling IS sensitive everytime.
>>
>>
>>
>>>Send signaling directly to the far-end, or use s/mime to encrypt the 
>>>SDP (good luck with that).
>>
>>
>>is it problematic to encrypt the SDP with S/MIME in your mind?
>>
>>regards,
>>michael
>>
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