Re: [Perc] Magnus Westerlund's Discuss on draft-ietf-perc-double-10: (with DISCUSS and COMMENT)

[Richard Barnes <[e-mail]>]

Hey Magnus,

Sorry, should have responded on Point 1.  I think you're just mistaken on
that point.  Padding is included within the inner encryption.  The double
transform is an SRTP transform like any other; outside of the SRTP stack,
there is no "inner" or "outer", just the same old protect and unprotect.
So padding works the same as it does with any other SRTP transform.

Was there some text in the document that gave you the impression that
padding was not included under the inner encryption?  The only mention of
padding I see in the document is in the figure in Appendix A [1], where the
padding is correctly shown to be within the inner encryption.  Happy to
clarify if you have some suggestions for how.

--Richard

[1] https://tools.ietf.org/html/draft-ietf-perc-double-11#appendix-A

On Mon, Aug 5, 2019 at 2:32 AM Magnus Westerlund <
[e-mail]> wrote:

> Hi,
>
> Sorry, I missed when this update was submitted, thanks for the reminder.
>
> The new version addresses most of my discuss, but missed to do anything
> about point 1 below.
>
> Otherwise it appears to address my discuss points. How do you want to
> resolve it?
>
> Cheers
>
> Magnus Westerlund
>
> > -----Original Message-----
> > From: Cullen Jennings <[e-mail]>
> > Sent: den 17 maj 2019 20:34
> > To: Magnus Westerlund <[e-mail]>
> > Cc: The IESG <[e-mail]>; [e-mail]; draft-ietf-perc-
> > [e-mail]; [e-mail]; [e-mail]
> > Subject: Re: [Perc] Magnus Westerlund's Discuss on
> draft-ietf-perc-double-
> > 10: (with DISCUSS and COMMENT)
> >
> > >
> > > 1. Section 5.1:
> > >
> > > To me it appears that one fundamental security flaw exists in the
> > > definition of the inner encryption. That is the fact that RTP padding
> > > is not included into the inner encrypted part. This prevents the
> > > application of RTP padding to prevent the potential privacy leakage
> > > that "Guidelines for the Use of Variable Bit Rate Audio with Secure
> > > RTP" (RFC 6562) documents. To prevent this type of information leakage
> > > and other privacy preserving operations based on applying RTP padding
> > > it would be necessary to include the RTP padding into the inner
> > > encrypted envelope. Appendix A figure indicates that is the case, but
> the
> > process description in 5.1 is not matching that.
> > >
> >
> > So my read of 5.1 is that does this. Clearly we need to make the text
> clear
> > that it does that - what part of the 5.1 makes you think the padding is
> > stripped from the  payload ?
> >
> > Perhaps to make it explicitly clear we should change
> >
> > "* Payload: The RTP payload of the original packet”
> >
> > to be
> >
> > "* Payload (including padding) The RTP payload (including passing) of the
> > original packet”
> >
> >
> >
> >
>
>