I have a laptop (Windows 8.1) and a desktop (Windows 7) with the exact same version of Chrome on (54.0.2840.99) but when visiting some sites, I get the following error.
Net:ERR_CERTIFICATE_TRANSPARENCY_REQUIRED
I only ever get it on the desktop though. I have tested the site on ssllabs.com and get a rating of A back.
What could the issue be? Would a difference in OS be causing it?
You didn't name any specific sites, but since this is a question from 2017 where there was no general CT enforcement I'm guessing that you were accessing a site with a Symantec/Symantec-subsidiary issued certificate.
Prior to the complete distrust they had been sentenced that all certs starting from 2016-06-01 would have to fulfill CT requirements.
See: https://security.googleblog.com/2015/10/sustaining-digital-certificate-security.html
And this means that Chrome would require a special bits of additional information to come along with a certificate. These are called SCTs (Signed Certificate Timestamps) and are sort of a proof of inclusion/proof of a promise to include that certificate in a CT log. Chrome required a number of SCTs, some from Google logs some from non Google logs.
And the longer the cert is supposed to be valid for the more SCTs you need.
And these SCT can have several different delivery mechanisms.
Details here: https://github.com/chromium/ct-policy/blob/master/ct_policy.md#qualifying-certificate
So I'm guessing that you were surfing to a site that served a Symantec-ish cert but didn't deliver enough SCTs to please Chrome.
