[VOIPSEC] Why a secure keyechange for media encryption?

Dan Wing dwing at fuggles.com
Fri Apr 28 11:00:12 PDT 2006


Michael Prochaska wrote:
> 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.

You should carefully separate active man-in-the-middle from
passive man-in-the-middle.  Just elevating an attack from a passive 
attack to an active attack is useful.

As well, determine if the man-in-the-middle would always need to *be* in 
the middle when you established a call with a remote peer.  Read ZRTP's 
specification and you'll pull out some of these ideas.

> in my mind there must be PKI clouds (providers, big companies - cross 
> certification) to assure  real secure communication.

Check out SPKI, RFC2692 and RFC2693.

-d

> 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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> 
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