Re: [rtcweb] AVPF [was: Encryption mandate (and offer/answer)]

Dzonatas Sol <dzonatas@gmail.com> Fri, 09 September 2011 19:42 UTC

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Date: Fri, 09 Sep 2011 12:46:12 -0700
From: Dzonatas Sol <dzonatas@gmail.com>
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Subject: Re: [rtcweb] AVPF [was: Encryption mandate (and offer/answer)]
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On 09/09/2011 12:23 PM, Alan Johnston wrote:
> Ekr is correct.  If we allow RTP, which I think is a mistake, then
> there is always a downgrade attack
>    

Two encrypted states that negotiate with each other is not an attack. 
There is just no obvious equality between the two "when introduced."

Let the federated servers introduce them; otherwise, it's browser to 
browser with the bigger unknown.

Maybe QoS can include syllabic gain performance measurements to test 
that continuously, yet that is forward-thinking for many despite known 
proof.

> My point was that if we must support insecure media, we could avoid
> the complexity of CapNeg by not requiring a single pass non-secure
> media negotiation.
>
> - Alan -
>
> On Fri, Sep 9, 2011 at 1:35 PM, Eric Rescorla<ekr@rtfm.com>;  wrote:
>    
>> On Fri, Sep 9, 2011 at 11:11 AM, Matthew Kaufman
>> <matthew.kaufman@skype.net>;  wrote:
>>      
>>> On 9/9/11 10:47 AM, Alan Johnston wrote:
>>>        
>>>> � The default will be SRTP - this can be
>>>> expressed in SDP without CapNeg. �Should the RTCWEB clients choose to
>>>> instead negotiate RTP, then this could be done with a second SDP
>>>> Offer/Answer exchange.
>>>>          
>>> I believe you've just designed a downgrade vulnerability.
>>>        
>> Unless I'm missing something, if you (a) support an insecure mode and (b) allow
>> negotiation of insecure vs. secure, there's not really any way to
>> avoid a downgrade
>> issue; the attacker can always pretend not to support security and how do you
>> know better? Obviously, it helps if you can negotiate the use or non-use of
>> media security over a secure-ish signaling channel, but that doesn't reduce
>> the threat from the signaling service.
>>
>> Best,
>> -Ekr
>>
>>      
> _______________________________________________
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> rtcweb@ietf.org
> https://www.ietf.org/mailman/listinfo/rtcweb
>
>    


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