Subject: [MMUSIC] Stephen Farrell's No Objection on draft-ietf-mmusic-sdp-mux-attributes-14: (with COMMENT)

From: "Stephen Farrell" <[email-masked]>
Date: Wed, 26 Oct 2016 02:50:06 -0700

Stephen Farrell has entered the following ballot position for
draft-ietf-mmusic-sdp-mux-attributes-14: No Objection

When responding, please keep the subject line intact and reply to all
email addresses included in the To and CC lines. (Feel free to cut this
introductory paragraph, however.)

Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
for more information about IESG DISCUSS and COMMENT positions.

The document, along with other ballot positions, can be found here:
https://datatracker.ietf.org/doc/draft-ietf-mmusic-sdp-mux-attributes/

----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

- 4.5 and 5.7: What if the different a=crypto lines
specify different strength ciphersuites? Wouldn't it be
better to pick the strongest or to say they MUST be the
same (as is done in 5.35)? If picking the first is the
right answer then maybe warn folks to not put a stronger
ciphersuite anywhere else?

- 5.36 vs. 5.39: It wasn't clear to me why these have
different rules - can you explain?

---

From: Suhas Nandakumar <[email-masked]>
Date: Wed, 26 Oct 2016 15:47:08 -0700

Hello Stephen

    Thanks for the review . please see inline.

> https://datatracker.ietf.org/doc/draft-ietf-mmusic-sdp-mux-attributes/

[Suhas]:  I did think about it some more and I am not sure the mux draft
opens up an vulnerability in this scenario.
For example, Even with the IDENTICAL category, the Offerer can include a
weak cipher in all the m=lines and thus force the Answerer to select the
weak one or have the Answerer reject the Offer. I am not sure if making it
iDENTICAL would help us guard against the wrong cipher selection.
.
In the TRANSPORT scenario, if the Answerer selected the m=line with a weak
cipher the Offerer has 2 options a) Don't include the weak cipher b) Do
another Offer/Answer with the modified list (with strong ciphers or
inactive media)

Please advise ..

> different rules - can you explain?
[Suhas] : It looks like both the fingerprint (Section 5.36) and
zrtp-hash(5.39) attributes have the same Multiplexing category of TRANSPORT
assigned and thus follow the same rules. Am i missing something here ?

> _______________________________________________
> mmusic mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/mmusic
>

---

From: Stephen Farrell <[email-masked]>
Date: Sun, 30 Oct 2016 21:50:57 +0000

Hiya,

> another Offer/Answer with the modified list (with strong ciphers or

It's less an issue of creating a vulnerability as it is of
making it easier for people to end up in a situation where
they think they have better security than is in fact the
case. I think experience shows that disallowing differences
of that kind is a good plan. But I could understand if it
was the case that allowing such discrepancies made it easier
to get interop in some cases. I don't know if that latter
is the case.

> assigned and thus follow the same rules. Am i missing something here ?

In the ZRTP case you have a MUST and level == M. In the other
there's no MUST and it has level == B. At this point I forget
what those level things mean though;-)

S.