W3C home > Mailing lists > Public > public-webappsec@w3.org > March 2017

Re: Single Trust and Same-Origin Policy v2

From: Mike West <mkwst@google.com>
Date: Mon, 27 Mar 2017 11:49:29 +0200
Message-ID: <CAKXHy=erAWyxHHxKq0yJ14EUpNkW9258QtAX-vuP9ZTo-1YpXQ@mail.gmail.com>
To: John Wilander <wilander@apple.com>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>
Hey John! Thanks for continuing the conversation!

On Fri, Mar 24, 2017 at 8:25 PM, John Wilander <wilander@apple.com> wrote:

> *# Single Trust*
>
> Users have a few interface signals to decide if they trust a site. There’s
> the URL bar which may show the full URL, the origin, just the host, or the
> name of the organization for sites with EV certificates. The URL bar also
> conveys TLS status with padlocks, warnings, and colors. Recently, Chrome
> and Firefox started to warn about insecure password fields so that’s
> another great signal. Then there's the very subtle mixed passive content
> indicators. I’m sure there’s more.
>
> We argue that in addition to the above, websites should have the ability
> to tell users that only first party resources are involved in a web page.
>

As a quick note here (with the caveat that I am _not_ a UX expert), Felt,
et al. published "Rethinking Connection Security Indicators
<https://www.usenix.org/system/files/conference/soups2016/soups2016-paper-porter-felt.pdf>"
at SOUPS last year, and it's a really great read on the topic of security
UI. One of their conclusion is that users do not perceive the lack of a
"secure" icon as a warning. Accordingly, Chrome is moving to reduce the
number of indicators we show to users, and to focus more on indicators of
insecurity rather than security. Chrome's current UI is a stepping-stone on
the way to dropping the "green lock" indication of security for HTTPS in
favor of a "red triangle with an exclamation point" indication of
non-security for HTTP at some point in the future. That's a long way of
saying that adding new indicators is an uphill struggle that needs solid
justification.

While I can imagine that single-trustness might have some value for a
site's developer, I'm not clear about the value it would provide to the
site's users. Can you help me understand the decisions you think this would
enable?

We call this Single Trust – pages where there’s just one entity the user
> has to trust. This makes a lot of sense on pages with password fields and
> credit card fields but I personally would also like the inbox and message
> form where I interact with my physician to be single trust. Pages where you
> submit confidential news tips should also be single trust. And single trust
> would be great for pages where I’m supposed to interact through a plugin
> such as a bridge to a smart card reader.
>

Do you imagine single-trust as something users would be exposed to once in
a blue moon, when a trust decision really matters (the "confidential news
tips" case), or do you want to encourage it to be a pervasive expectation
for most sites a user visits?


> Ideally, single trust should be possible for multiple domains belonging to
> the same organization which is not possible through CSP alone. This leads
> us to …
>

As Bil noted below, the DNS-level carveout means that "belonging to the
same organization" can't be a strong guarantee. The name belongs to the
organization, but the service being named may well be outsourced. You
suggest below that "From a user standpoint, the single trust is in the
organization that takes responsibility for requests and responses.", but
can you talk a little bit about the ways in which the status quo fails to
offer the same guarantee? Isn't an organization that relies on third-party
ads "tak[ing] responsibility" for those requests by adding the ad calls and
forming a contractual relationship with the provider?

If single trust gives real advantage to developers, I worry that it will
simply devolve into delegating a set of subdomains to a third-party (`
ads.example.com`, `provider1.ads.example.com`, `provider2.ads.example.com`,
and so on). Given revenue concerns, the slope doesn't seem that slippery. :)

*# Same-Origin Policy v2*
>
> Good TLS and the same-origin policy are the cornerstones of web security
> and for a single domain it works just fine. But we end up with tradeoffs
> since the SOP considers apple.com and icloud.com as different as apple.com and
> europa.eu. The most well-known tradeoff is third-party cookies but there
> are tradeoffs for third-party frames, Fetch, workers, and storage. If we
> apply strict rules on third parties we hamper cross-site ecosystems such as
> single sign-on and site integration. If we instead loosen up the rules we
> get cross-site security breakdown and/or third-party tracking.
>
> We would like to discuss how to technically implement a secure SOP v2 that
> takes domain control/ownership into account. This would allow:
>
>    - Seamless single sign-on across domains with one owner.
>
> Both Google (Smart Lock for Passwords
<https://developers.google.com/identity/smartlock-passwords/android/associate-apps-and-sites>)
and Apple (Shared Web Credentials
<https://developer.apple.com/reference/security/shared_web_credentials>)
are shipping ~similar solutions to this problem for the specific case of
password managers. Developers are asked to put a file somewhere on their
domain that lists a set of origins and apps that are associated with each
other, and stored credentials are made available in various ways across
those associations.

Though both end up using their respective app stores as a root of trust, it
would be interesting to compare the `assetlinks.json` and
`apple-app-site-association` file contents to see if there's a cowpath
waiting to be paved here. It's probably also worth looking at past efforts
like DBOUND <https://datatracker.ietf.org/wg/dbound/charter/> to see if we
can learn anything from their struggles to get something like this defined
and shipping.

>
>    - Seamless integration across domains with one owner, such as
>    messaging between frames and access to storage.
>
> This worries me a bit. As Eduardo noted earlier, Google uses subdomains
explicitly to break the integration between applications living on/under `
google.com`. I think it's pretty unlikely that Google would opt-into a
system that gave `accounts.google.com` script access to `youtube.com` (and
would be even more unlikely to adopt the inverse), for instance.

Do you have some concrete use-cases you'd like to enable here that are
difficult in the status quo via `postMessage()`, etc? You suggest that we
could make this "much more elegant", but I don't understand how. :)

>
>    - Much better transparency and rules around third-party resources.
>
> What does this encompass?

Thanks again!

-mike
Received on Monday, 27 March 2017 09:50:23 UTC

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