Re: [secdir] Security review of draft-ietf-rtcweb-fec-08 (was Re: Security review of draft-ietf-perc-srtp-ekt-diet-08)

Justin Uberti <justin@uberti.name> Sat, 09 February 2019 01:51 UTC

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From: Justin Uberti <justin@uberti.name>
Date: Fri, 8 Feb 2019 17:51:32 -0800
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To: Hilarie Orman <hilarie@purplestreak.com>
Cc: Ben Campbell <ben@nostrum.com>, The IESG <iesg@ietf.org>, secdir@ietf.org, draft-ietf-rtcweb-fec all <draft-ietf-rtcweb-fec.all@tools.ietf.org>
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Subject: Re: [secdir] Security review of draft-ietf-rtcweb-fec-08 (was Re: Security review of draft-ietf-perc-srtp-ekt-diet-08)
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Any suggestions on the sort of text you would like to see?

e.g. "In the WebRTC context, FEC is specifically concerned with recovering
data from lost packets; any corrupted packets will be discarded by the SRTP
decryption process. Therefore, as described in [RFC3711], Section 10..."

On Fri, Feb 8, 2019 at 5:46 PM Hilarie Orman <hilarie@purplestreak.com>
wrote:

> I think that the purpose of the FEC should be explicit, else the
> interaction with
> encryption will remain a source of confusion forever.
>
> Hilarie
>
> ----- Original Message -----
> From: Justin Uberti <justin@uberti.name>
> To: Ben Campbell <ben@nostrum.com>
> Cc: Hilarie Orman <hilarie@purplestreak.com>om>, The IESG <iesg@ietf.org>rg>,
> secdir@ietf.org, draft-ietf-rtcweb-fec all <
> draft-ietf-rtcweb-fec.all@tools.ietf.org>
> Sent: Fri, 08 Feb 2019 18:20:41 -0700 (MST)
> Subject: Re: Security review of draft-ietf-rtcweb-fec-08 (was Re: Security
> review of draft-ietf-perc-srtp-ekt-diet-08)
>
> On Fri, Feb 1, 2019 at 2:49 PM Ben Campbell <ben@nostrum.com> wrote:
>
> > Hi,
> >
> > Please note that this review is for draft-ietf-rtcweb-fec-08, not the
> PERC
> > draft referenced in the subject.
> >
> > Thanks!
> >
> > Ben.
> >
> >
> > > On Feb 1, 2019, at 1:42 AM, Hilarie Orman <hilarie@purplestreak.com>
> > wrote:
> > >
> > > Security Review of WebRTC Forward Error Correction Requirements
> > > draft-ietf-rtcweb-fec-08
> > >
> > > Do not be alarmed.  I have reviewed this document as part of the
> > > security directorate's ongoing effort to review all IETF documents
> > > being processed by the IESG.  These comments were written primarily
> > > for the benefit of the security area directors.  Document editors and
> > > WG chairs should treat these comments just like any other last call
> > > comments.
> > >
> > > The document describes the appropriate uses of FEC for web content when
> > > using WebRTC.  It also describes how to indicate that FEC is being
> used.
> > >
> > > The Security Considerations mention the possibility of additional
> network
> > > congestion when using FEC.  Although this can be a problem, I do not
> > think
> > > it is a security issue, thus it does not belong in this section.
> >
>
> Understood. I think this paragraph could easily be moved to the preceding
> section.
>
> > >
> > > There is a security-related issue wrt to FEC and encryption.  If the
> > > error model is that message blocks may be lost but not altered in
> > > transit, then FEC with encryption is fine.  But if FEC is added for
> > > the purpose of correcting corrupted bits in a message block, then it
> > > is important that FEC is done after encryption.  The draft seems to
> > > ignore the issue, and it also seems to recommend a processing scheme
> > > that would result in encryption of the FEC data.  If there is a body
> > > of practice for other IETF FEC protocols that explains these issues,
> > > an explicit reference to it in the Security Considerations would be
> > > very helpful.
> >
> > FEC is added specifically to protect against lost blocks. Any corruption
> of the blocks will be detected by the decryption procedure, and such blocks
> will be discarded.
>
> There is a reference to RFC 3711, which stipulates the fec-then-encrypt
> ordering. RFC 3711 is admittedly terse on this subject, but it is quite
> clear about the ordering.
>
>