Google Chrome will no longer check for revoked SSL certificates online

Google plans to remove online certificate revocation checks from future versions of Chrome, because it considers the process inefficient and slow.

Browsers currently check if a website's SSL certificate has been revoked by its issuing Certificate Authority (CA) when trying to establish an HTTPS connection. These checks are done by querying CA-operated servers through a special protocol known as OCSP (Online Certificate Status Protocol).

The problem is that browsers can't always communicate with the validation servers because of various technical problems and when something like this happens, the HTTPS connections should not be established; at least in theory.

However, because these failures can have a serious usability impact, especially when CAs experience server downtime, browser vendors have decided ignore revocation checks that result in network errors. This is a referred to as a soft-fail.

"An attacker who can intercept HTTPS connections can also make online revocation checks appear to fail and so bypass the revocation checks," Google security engineer Adam Langley said in a blog post on Sunday.

"So soft-fail revocation checks are like a seat-belt that snaps when you crash," he said. "Even though it works 99% of the time, it's worthless because it only works when you don't need it."

This suggests that online certificate revocation checking doesn't add a lot of value to Web security in its current implementation. However, keeping it on comes at a significant cost -- browsing speed.

"The median time for a successful OCSP check is ~300ms and the mean is nearly a second," Langley said. "This delays page loading and discourages sites from using HTTPS."

After considering the drawbacks, Google decided to remove OCSP checks from future versions of Chrome and replace them with a local list of revoked certificates that can be updated without requiring a browser restart. Attackers could theoretically block the update process, but this will require more effort than blocking an OCSP revocation check, Langley said.

The security engineer invited CAs to voluntarily contribute their revoked certificates to the list by publishing them in a format and place that's accessible to Google's crawler.

Experts have raised serious questions about the security and reliability of the current SSL infrastructure during recent months, following security breaches at several CAs that resulted in rogue certificates being issued. Various proposals for improving or replacing the current system are being discussed.

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