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Re: 9.2.2 Cipher fallback and FF<->Jetty interop problem

From: Cory Benfield <cory@lukasa.co.uk>
Date: Thu, 18 Sep 2014 09:33:15 +0100
Message-ID: <CAH_hAJHrhY1nQAHQ_o0uVPuqccLDzYAyNEuZ6q1Dh4ePDBKA_A@mail.gmail.com>
To: Greg Wilkins <gregw@intalio.com>
Cc: Stuart Douglas <stuart.w.douglas@gmail.com>, Martin Thomson <martin.thomson@gmail.com>, Brian Smith <brian@briansmith.org>, Ilari Liusvaara <ilari.liusvaara@elisanet.fi>, HTTP Working Group <ietf-http-wg@w3.org>
Greg, I've rearranged your post below because I found it flowed weirdly.

On 18 September 2014 06:21, Greg Wilkins <gregw@intalio.com> wrote:
> I don't actually agree with the premise that browser vendors are that
> morally corrupt.  I think they have a difficult line to walk between
> offering reasonable security and wide spread connectivity.       If they are
> offering old ciphers then I am sure that there are significant origin
> resources that can only be accessed with them.

Alright, this makes sense. We agree on the original premise, but let
me state it outright: all user-agents are strongly incentivized to
make as many connections as they possibly can. Being unable to provide
a resource to a user almost always costs you that user. Users rarely
pick a browser (e.g. Chrome), try to connect to a resource and find
that it fails where another browser (say IE) succeeded, and then say
"Thankyou Chrome for protecting me from myself!" They say "Chrome
sucks and doesn't work". This is the exact same reason Microsoft have
long had a team whose sole purpose is to specially code bugs *back in*
to new Windows versions to prevent programs breaking.

Most users will never thank a user-agent for making them more secure,
but they will always blame a user-agent for refusing to fetch
information for them. If there is a competitor user-agent that makes
them less secure but gives them access to a resource they want,
they'll just switch to that. Given that most browsers are not
charities, it cannot be a surprise that they aim to increase their
market share. Everyone is very nice in this forum because civility is
good and the world is made better by us all getting a bite at the
apple, but don't for a moment think that we're not all in some form of
competition.

> So he is saying that because browser vendor value market share more than
> their users security it is apparently our job to withhold the h2 protocol or
> just fail to connect in an  effort to push them towards being good web
> citizens.

No, this responsibility goes both ways. I, a user-agent provider, am
just as responsible as you to ensure good web citizenship. If hyper
connects to Jetty, does the ALPN handshake, and then finds a block
cipher has been negotiated, I am just as responsible as you for
tearing that connection down. The correct statement here is that "good
web citizens" are responsible for holding "bad web citizens" to
account.

I am confident that browsers will abide by the requirement in the
draft spec to tear down h2 connections to servers that don't negotiate
secure ciphers per 9.2.2. Everyone on this list will be working
together on this point (I hope). So the responsibility is not just for
you.

> But let's accept the premise that browser vendors are indeed morally corrupt
> and will deploy insecure ciphers rather than lose market share.

Why would anyone accept this premise? Especially with the loaded
language. I will accept a related premise: "browser vendors are
running businesses, and have an inclination to serve their own
financial best interests as well as the interests of their users". I
don't assume that *anyone* on this list is morally corrupt: I have
seen no evidence for this fact.

> Let's also
> assume that origin server deployers are also prepared to accept those bad
> ciphers and make their content available over them...  I have absolutely no
> idea how allowing those two to tango over http/1 rather than h2 pushes them
> to any better security practises.

It doesn't. None of the design goals I have ever seen for h2 include
making http/1 more secure. Why would they? And besides, what could the
spec possibly say? "If you negotiate h2 with insecure ciphers, tear
down the connection and refuse to ever allow connections from that
peer again"? If the connection fails, *clearly* a http/1 connection
can be made, so any ruling in the h2 spec does nothing to prevent what
you just discussed.

> Perhaps the failing abysmally to connect
> part might be a bit more persuasive, but I expect that is more likely to
> make them remove the good ciphers.

Yes it would. Again, server vendors want as many clients to be able to
connect to them as possible.

> If failure to connect is a driver to better cipher policy, then  we need not
> hobble h2 to achieve that.  Instead the browser vendors and server deployers
> can simply grow a pair and remove the bad ciphers.

Failing to connect is not a driver to good security policy, it's a
driver to *bad* security policy. Good security policy refuses
connections, bad security policy accepts them. And there will always
be pressure to make connections where others cannot. This is why
browsers let you browse to website with expired certs, it's why
libraries let you turn off certificate verification, and it's why
servers let you say you'll accept the TLS NULL cipher: because if they
don't, others will.

I don't think anyone in this list is a bad internet citizen because
we're all here trying to make it better! We've all got a vested
interest in the web being the best it can be. The problem is that us
taking the moral high ground leads to users picking up projects that
don't take the moral high ground. Absolutism here doesn't help anyone.
We have to work with what we've got. We have to be as secure as we can
be without driving users to implementations that don't care about
security.

Greg, I'm genuinely sympathetic to your original complaint. I've had
problem with cipher suites as well, and have accepted that the best I
can do is fail if the server screwed up. I don't like that approach.
But I think the goal of section 9.2.2 is laudable and I'd be loathe to
remove it without replacing it with something equally important.

Cory
Received on Thursday, 18 September 2014 08:33:42 UTC

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