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

[Suhas Nandakumar <[e-mail]>]

Hey Magnus

   Wondering if Richard's response answers your question?

Thanks
Suhas

On Mon, Aug 5, 2019 at 7:48 AM Richard Barnes <[e-mail]> 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 <
> [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”
>> >
>> >
>> >
>> >
>>
>>