Contact [email protected]

ExplainerNone

Specificationhttps://datatracker.ietf.org/doc/rfc9163

Summary

Expect-CT is an HTTP header that allowed websites to opt in to Certificate
Transparency enforcement before it was enforced by default. It also has
reporting functionality to help developers discover CT misconfigurations.


Blink componentInternals>Network>DomainSecurityPolicy
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Internals%3ENetwork%3EDomainSecurityPolicy>

Motivation

Expect-CT was designed to help transition to universal Certificate
Transparency (CT) enforcement, by allowing high-value websites to opt in to
CT enforcement/reporting for better security before CT enforcement was
required (by Chrome) on all public websites. However, Expect-CT has now
outlived its usefulness. Chrome requires CT on all public websites now, so
there is no security value to Expect-CT anymore. Expect-CT was also
designed to help site owners discover CT-related misconfigurations;
however, now that CT is universally required, CT is generally configured in
websites' certificates by certificate authorities and virtually never
configured by individual site owners, thus Expect-CT has very limited value
as a misconfiguration/debugging tool anymore either. No other browser has
implemented Expect-CT so removing it is not an interoperability concern.


Initial public proposal
https://groups.google.com/a/chromium.org/g/blink-dev/c/tgn5R-58iek/m/Q6YCnu0RFQAJ

TAG reviewn/a

TAG review statusNot applicable

Risks


Interoperability and Compatibility


No other browser has implemented Expect-CT or given signals that they
intend to (to my knowledge). Expect-CT is not user-visible so removing the
feature has no compatibility risk. Developers who are currently sending the
header should stop doing so just to save the bytes on the wire.

While the header is served on a large percent of requests (~6%), this is
likely due to a small number of large providers that can be informed of the
deprecation via 1:1 outreach. As described above, the header serves no
security value any longer, removing it will have no user-visible effects,
and the header provides extremely minimal debugging value to developers
since developers are no longer responsible for serving their own CT
information (100.00% of requests serve CT information directly embedded in
the certificate, which developers are not responsible for configuring).

*Gecko*: No signal

*WebKit*: No signal

*Web developers*: No signals

*Other signals*:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that
it has potentially high risk for Android WebView-based applications?



Debuggability

We'll add a console message informing developers that the header will/has
no effect and they should remove it.

Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>
?No

Flag name

Requires code in //chrome?False

Estimated milestones

No milestones specified


Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/6244547273687040

This intent message was generated by Chrome Platform Status
<https://chromestatus.com/>.

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