Google announced that it has removed all trust in WoSign and StartCom certificates from Chrome and Android, following the discovery that the two certificate authorities misbehaved.
WoSign/StartCom Go Rogue
About a year ago, Mozilla uncovered that a Chinese Certificate Authority (CA) called WoSign had a number of technical and management failures, which included bypassing previous restrictions by browser vendors on distributing SHA-1 certificates.
The browser vendors had previously agreed not to accept SHA-1 certificates that were issued after January 2016. However, WoSign backdated its certificates so it could continue to issue SHA-1 certificates that would still be supported by the browsers (for legacy reasons).
Mozilla also found out that WoSign had secretly acquired a smaller CA, StartCom, which was against its CA policies.
WoSign previously denied both allegations, until Mozilla and others came up with sufficient evidence to show that the allegations were indeed true. The level of deception coming from WoSign was also what prompted Mozilla to plan a progressive removal of WoSign and StartCom’s certificates. Apple and Google followed with a similar plan.
Plans To Distrust WoSign/StartCom Certificates
Mozilla started phasing out these certificates in Firefox 51, while Google did the same thing starting with version 56 of Chrome, both of which came out last Fall. Google now seems ready to completely eliminate the support for WoSign and StartCom certificates from its browser.
Google initially whitelisted the top 1 million websites for using the WoSign/StartCom certificates, but it gradually reduced the length of that whitelist over the course of several Chrome releases. Starting with version 61 --we’re now at 59--Google will completely remove support for WoSign and StartCom certificates from Chrome.
This means that websites that are still using these certificates by the time Chrome 61 comes out will appear broken in the browser and won’t load for users of that particular Chrome version (as well as all the other versions coming afterward). Google recommended sites that still use WoSign and StartCom certificates to immediately replace them so as to not risk disruption of service for potentially a large portion of their users.
No More Mr. Nice Browser Vendor
Over the past couple of years, Google has shown that it’s not willing to compromise the security of its users if some of the CAs misbehave, no matter how large they are. Google has taken some severe measures against both WoSign and Symantec, one of the largest CAs, to ensure that they properly validate their certificates and follow the rules. This may have also led Symantec to consider the sale of its CA business.
The CA rules are important, because without them, the whole HTTPS security ecosystem could collapse. If users can’t trust the HTTPS connections to be secure anymore, then they may not make certain transactions or communications over the internet. Alternatively, they could switch to alternative encryption communications protocols, which may come with their own benefits and compromises.
The decisions to punish CAs by some of the major browser vendors, such as Google and Mozilla, must not have come easy. Banning a CA from the browser could easily turn into a PR battle if thousands of websites' users can't visit anymore because of broken certificates.
Ultimately, it’s still the site operators' responsibility to educate themselves on their certificates' security and ensure that their users’ connections to the site are protected. That includes not using certificates from CAs that don’t follow the rules or replacing them when necessary.
Google has also been promoting (and soon requiring) support for the Certificate Transparency certificate logging and monitoring system, which should make it much easier to identify when a CA is issuing problematic certificates. It should also encourage CAs to behave and to properly audit their own systems to ensure everything works as it should and that bad actors (whether hackers or malicious employees) aren’t abusing their systems to issue forged certificates.