W3C home > Mailing lists > Public > public-webappsec@w3.org > December 2014

Public Key Pinning (was Re: [blink-dev] Re: Proposal: Marking HTTP As Non-Secure)

From: Jeffrey Walton <noloader@gmail.com>
Date: Sat, 27 Dec 2014 18:12:48 -0500
Message-ID: <CAH8yC8kmcfO6DLD5+rX4Be6_VSZeQAzpyCD+ixrkTtN=y8HHDw@mail.gmail.com>
To: rsleevi@chromium.org
Cc: "dev-security@lists.mozilla.org" <dev-security@lists.mozilla.org>, "public-webappsec@w3.org" <public-webappsec@w3.org>, security-dev <security-dev@chromium.org>, blink-dev <blink-dev@chromium.org>
Hi Ryan,

Sorry about the extra chatter.

>>> The control to stop most of the intercept related attacks - public key
>>> pinning - was watered down by the committee members to the point that
>>> the attacker effectively controls the pinset. (Here, I'm making no
>>> differentiation between the "good" bad guys and the "bad" bad guys
>>> because its nearly impossible to differentiate between them).
>
> To Jeffrey: can you please stop the ad hominem attacks

The authors should not take it personally. I've taken care not to name
any names or teams. In the end, its not the authors but the
organization bodies like the IETF.

Holding an author responsible is kind of like holding a soldier
responsible for a war. The buck stops with organizations like the
IETF. Or in the case of war, with the politicians or leaders. In both
cases, its a failure of leadership.

In this thread (https://www.ietf.org/mail-archive/web/websec/current/msg02261.html),
Chris Palmer suggested using shame as a security control. I get what
he was saying. When the IETF approves an externaltiy to control
security parameters like they did in this case, then they should
expect a little shame. Sunshine is the best disinfectant.

> Especially when the
> three authors have all worked on Chromium, and two are actively championing
> this proposal?

Three points here.

First and foremost, YES, the authors have done good work.

Second, there are some gaps and I think things should be improved.

Things should be improved because we have a pretty good idea of how
bad things can be (are?) because of Snowden. Its not just nosy
organizations, nosy OEMs and manufacturers, and oppressive regimes -
its friendly regimes, too. I could be wrong, but I think that includes
just about everyone.

We also know how to improve them, so no one is working in a vacuum
here. There's nothing bleeding edge about this stuff.

Third, as a side note, I *personally* want things improved because I
want to use and rely on this control. This is *not* me arguing
theoretically with folks. I often don't have a say in the application
type (web app, hybrid app, native application), so I'm always
interested in improving the web apps because they are security control
anemic.

> This sort of revisionist history does no one any good. It is
> a simple threat model: If you give up administrative access to your physical
> device, it is no longer your device.

Three points here.

First, history is important and this issue is significant. The issue
is significant because it was a big leap forward in security. When the
issues are raised publicly, they can be addressed. Again, sunshine is
the best disinfectant.

Second, at the design level, this particular risk that can be
controlled. Pinning the public keys is the control under many
scenarios. But a modified pinning scheme was offered, which (if I am
running through the use cases properly), pretty much leaves the
original problem untouched.

Third, it''s a leap: the site never gave anything away. It was taken
away from them and given to an externality. I even argue the user did
not give anything away. Most users don't have a security engineering
background, and therefore cannot make that decision. In this case, it
was *surreptitiously* taken away from them and given to an
externality.

> The thing you lament missing due to
> some shadowy committee members (hi! No shadows here!)

Guilty. I do have a suspicious mind :)

> ... if your device is physically owned, it is
> physically owned, and no remote server can express a policy that clients
> will not be able to override, short of Trusted Computing and Remote
> Attestation

OK, two points here.

First, pleading one short coming (such as all software has flaws, like
the firmware, loader and OS) and then claiming its a reason another
flaw (its OK for my application to be defective because there are
lower level defects the attacker can use) is simply bullocks. If
that's really the argument being made, then do away with HTTPS
altogether because there's always going to be a flaw somewhere (even
in HTTPS/PKI{X} itself).

Second, the attacker is a network attacker, and not a physical
attacker. So while the device may be owned (i.e., its got an
untrustworthy CA; or the firmware, loader, OS and application has
flaws), the attacker is only effective at the network level. In this
case, the software can provide effective controls to reduce risk.

I am aware there are residual risks. If the attacker steps up his
game, then we will look at other controls.

> I've avoided commenting all of the other times you've misrepresented how
> this came to be, but lest it be seen that our silence is assent, I have to
> at least call out this dissent.

I think its good that you raised the counterpoints.

----------

As a post script, I have two open questions. Perhaps you can help set
the record straight for posterity.

First, the open question of: why was circumvention added and why was
the policy element to stop circumvention taken away? In this thread
(https://www.ietf.org/mail-archive/web/tls/current/msg14722.html),
Yoav Nir claimed the policy element was removed because there was no
support for it. But that's a symptom, and not the reason.

I suspect it is primarily related to advertising, buts its just
speculation. Under the Advertising Theory, revenue is generated when
the message gets through, so the message must always get through.
Stopping the message because the channel is known insecure is not an
option for the business model.

Second, the open question of: why is the application relying on the
platform to perform pinning in a TOFU scheme? Why is the application
itself not allowed to perform the pinning at the application level? If
the application pins, it no longer a TOFU scheme because the
application is leveraging its *a priori* knowledge.

For example, WebSockets does not provide methods to query connection
security parameters. With things like trusted distribution channels,
application stores and side loaded trusted code, I don't have to worry
too much about tampering in transit. That means applications like the
Self Serve, Single Password Sign-On Change application can be assured
with a high degree of certainty its passing its high value data to the
right server, and not some middleware box or an imposter.

Jeff
Received on Saturday, 27 December 2014 23:13:15 UTC

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