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

Magnus Westerlund <magnus.westerlund@ericsson.com> Thu, 29 August 2019 14:19 UTC

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From: Magnus Westerlund <magnus.westerlund@ericsson.com>
To: "rlb@ipv.sx" <rlb@ipv.sx>
CC: "fluffy@iii.ca" <fluffy@iii.ca>, "perc@ietf.org" <perc@ietf.org>, "suhasietf@gmail.com" <suhasietf@gmail.com>, "iesg@ietf.org" <iesg@ietf.org>, "perc-chairs@ietf.org" <perc-chairs@ietf.org>, "draft-ietf-perc-double@ietf.org" <draft-ietf-perc-double@ietf.org>
Thread-Topic: [Perc] Magnus Westerlund's Discuss on draft-ietf-perc-double-10: (with DISCUSS and COMMENT)
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Date: Thu, 29 Aug 2019 14:19:20 +0000
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Subject: Re: [Perc] Magnus Westerlund's Discuss on draft-ietf-perc-double-10: (with DISCUSS and COMMENT)
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Hi,

I will clear when the new version is available or an RFC-editor note to
this affect has been included. 

Cheers

Magnus

On Thu, 2019-08-29 at 09:50 -0400, Richard Barnes wrote:
> Easy enough.  I think RFC 3711 is clear enough, but if you want it to
> be more explicit, so it shall be.  I just copied over the language
> from 3711.
> 
> https://github.com/ietf/perc-wg/pull/174
> 
> 
> 
> On Thu, Aug 29, 2019 at 5:50 AM Magnus Westerlund <
> magnus.westerlund@ericsson.com> wrote:
> > Hi,
> > Hi,
> > 
> > 
> > Back from vacation. 
> > 
> > No Richards explanation doesn't help. Section 5.1 contains a
> > normative
> > description of how to create a synthetic packet. That description
> > is
> > not expplicit that the padding shall be part of the information
> > that is
> > included. Thus, implicitly the described procedure forbidds
> > padding.
> > Per RFC 3550 the padding is not part of the payload thus the need
> > for
> > being explicit about that the padding is to be included here. 
> > 
> > My suggestion is still that the following bullet: 
> > 
> >  *  Payload: The RTP payload of the original packet
> > 
> > Is changes to be explicit that padding is to be included:
> > 
> > "* Payload: The RTP payload (including
> >    padding) of the original packet”
> > 
> > Any other way that makes it explcit that the origianl packets
> > padding
> > is to be included is fine by me. But it does need to be explcit.
> > 
> > Cheers
> > 
> > Magnus
> > 
> > On Fri, 2019-08-16 at 07:46 -0700, Suhas Nandakumar wrote:
> > > Hey Magnus
> > > 
> > >    Wondering if Richard's response answers your question?
> > > 
> > > Thanks
> > > Suhas
> > > 
> > > On Mon, Aug 5, 2019 at 7:48 AM Richard Barnes <rlb@ipv.sx> wrote:
> > > > 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 <
> > > > magnus.westerlund@ericsson.com> 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 <fluffy@iii.ca>
> > > > > > Sent: den 17 maj 2019 20:34
> > > > > > To: Magnus Westerlund <magnus.westerlund@ericsson.com>
> > > > > > Cc: The IESG <iesg@ietf.org>; perc-chairs@ietf.org; draft-
> > ietf-
> > > > > perc-
> > > > > > double@ietf.org; suhasietf@gmail.com; perc@ietf.org
> > > > > > 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”
> > > > > > 
> > > > > > 
> > > > > > 
> > > > > > 
> > > > > 
-- 
Cheers

Magnus Westerlund 


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