Does trustd leak information about users' software usage to Apple and/or third parties?
macOS (as implemented in November 2020) occasionally sends out “some opaque information about the developer certificate of apps” based on timeouts and if it detects the ability to connect to Apple servers to check for certificate revocation.
Apple has also announced some substantial improvements as a result of last week’s events. They also fixed what I termed a “rookie mistake” of inadequately documenting and committed publicly to addressing the architecture of this feature. Time will tell how fast these roll out and if the systems are more resilient without compromising agility to contain malware and react to revoked certificates.

https://support.apple.com/en-us/HT202491


Gatekeeper performs online checks to verify if an app contains known malware and whether the developer’s signing certificate is revoked. We have never combined data from these checks with information about Apple users or their devices. We do not use data from these checks to learn what individual users are launching or running on their devices.
These security checks have never included the user’s Apple ID or the identity of their device. To further protect privacy, we have stopped logging IP addresses associated with Developer ID certificate checks, and we will ensure that any collected IP addresses are removed from logs.
In addition, over the the next year we will introduce several changes to our security checks:

A new encrypted protocol for Developer ID certificate revocation checks
Strong protections against server failure
A new preference for users to opt out of these security protections



The best two technical write ups I have seen of what in hindsight looks like a rookie mistake by Apple about inadequate documentation on how trustd functions made a bad day much worse for Apple and people that support or use macOS.

https://blog.jacopo.io/en/post/apple-ocsp/ (credit to Jacopo Jannone for the wording of “some opaque information”)
https://lapcatsoftware.com/articles/ocsp.html

The best non-technical summary (but also based on technical analysis and background) is John Gruber’s summary.

Just an embarrassing bug for Apple on a high-profile launch day.


https://daringfireball.net/linked/2020/11/14/macos-trustd-bug

The failed or congested OCSP service did cause a very widespread denial of service outage on macOS client computers November 12, 2020 for more than 90 minutes.

A crucial difference between OCSP and notarization is that the latter is only checked on first launch of the app. The notarization status is cached permanently and has no expiration, unlike OCSP. Thus, notarization only affects your ability to install new apps, it doesn't affect your ability to launch already installed apps.

I am certain that security researchers are probing these services heavily and some will publish think pieces whether or not Apple has made mistakes. If Apple has, I expect some to collect substantial bounty by responsibly reporting if user privacy is being actively compromised.

https://developer.apple.com/security-bounty/