Re: [AVTCORE] Fwd: I-D Action:draft-lennox-avtcore-srtp-encrypted-header-ext-00.txt

[Qin Wu <[e-mail]>]

----- Original Message ----- 
From: "Jonathan Lennox" <[e-mail]>
To: "Qin Wu" <[e-mail]>
Cc: <[e-mail]>
Sent: Friday, May 06, 2011 9:29 AM
Subject: Re: [AVTCORE] Fwd: I-D Action:draft-lennox-avtcore-srtp-encrypted-header-ext-00.txt


On May 5, 2011, at 9:25 PM, Qin Wu wrote:

> [Qin]: I agree using the same keystream to encrypt twice  will cause two-time pad security failure issue,
> i.e., first use the keystream to encrypt STRP payload, and then use the same keystream to encrypt 
> header extension elements.
> 
> However if we regard the payload of header extension elements and SRTP payload as a big payload, 
> we only need to use the same keystream to encrypt this big payload once. there is no two-time pad 
> security issue, right?

That's true, but it wouldn't be backward-compatible with existing receivers, which understand SRTP but ignore extension headers they're not familiar with -- the keystream would start in the wrong place.

[Qin]: So who will care header extension elements? the intermediary node or receiver who are signalled by SDP.
--
Jonathan Lennox
[e-mail]