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

Sean Turner <sean@sn3rd.com> Wed, 13 February 2019 02:38 UTC

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From: Sean Turner <sean@sn3rd.com>
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Date: Tue, 12 Feb 2019 21:38:14 -0500
Cc: Justin Uberti <justin@uberti.name>, Ben Campbell <ben@nostrum.com>, draft-ietf-rtcweb-fec all <draft-ietf-rtcweb-fec.all@tools.ietf.org>, The IESG <iesg@ietf.org>, secdir@ietf.org
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References: <201902010742.x117gdGm030846@rumpleteazer.rhmr.com> <F44FA6A0-4599-4BFF-8BEB-C67774714762@nostrum.com> <CALe60zD=OeTfjof3Q5UqnJRHsAQC-kS1oZYaQZ5HahAVOJgVKQ@mail.gmail.com> <240284129.169422738.1549676775109.JavaMail.zimbra@purplestreak.com> <CALe60zA6qwLLHpHHDp4Y5_PAX-wfBUmqw3gd5OWGx0zFJ57tvw@mail.gmail.com> <1466140720.170234113.1549687106882.JavaMail.zimbra@purplestreak.com>
To: Hilarie Orman <hilarie@purplestreak.com>
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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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Hilarie,

Justin produced this PR to address this:
https://github.com/juberti/draughts/commit/6e991d1eeaf1e505bb89957319be38df4ada56f5

Cheers,

spt

> On Feb 8, 2019, at 23:38, Hilarie Orman <hilarie@purplestreak.com> wrote:
> 
> OK, that's good.
> 
> Hilarie  
> 
> -- 
> 
> 
> ----- Original Message -----
> From: Justin Uberti <justin@uberti.name>
> To: Hilarie Orman <hilarie@purplestreak.com>
> Cc: Ben Campbell <ben@nostrum.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 18:51:32 -0700 (MST)
> Subject: Re: Security review of draft-ietf-rtcweb-fec-08 (was Re: Security review of draft-ietf-perc-srtp-ekt-diet-08)
> 
> 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.
>> 
>> 
> 
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