Google Chrome attempts to use the root certificate store of the underlying operating system to determine whether an SSL certificate presented by a site is indeed trustworthy, with a few exceptions.
In order for Chrome to be able to trust a root certificate, it must either be included by the underlying operating system or explicitly added by users. If you are a root CA, the following contacts should be used:
Google Chrome maintains a hard-coded list in the binary of which root certificates are "EV-Qualified", along with the appropriate OID that must appear on certificates issued from that root to be considered EV certificates. If you are a root CA who issues EV certificates and Google Chrome does not already recognize these certificates as EV certificates, please file a bug in our bug tracker (http://bugs.chromium.org/new) including the name of your CA, the fingerprint of your EV root, the OID you use to issue EV certs, a link to your WebTrust for CAs - EV audit, and a link to a server hosting a test or real certificate issued from this root.
On Apple OS X, Google Chrome currently uses the System Keychain to determine which root certificates are EV-Qualified. To ensure certificates issued from your root are considered EV certificates, please contact the Apple Root Certificate Program for inclusion. Please note that this may change at any time, so inclusion within the Google Chrome hard-coded list is recommended.
From 1 January 2015, Google Chrome requires all EV certificates to use Certificate Transparency. Full details can be found in EVCTPlanMay2015edition.pdf.
Google Chrome reserves the right to distrust root certificates present in the operating system's root certificate list. At the core of trust in the PKI system is the fact that the operation of Root CAs is beyond reproach. If one of these guardians of trust were to operate in a non-trustworthy way, it would be no different than a police officer who was covering up a crime or protecting the identity of a criminal (because it reflected personally on the officer), or a firefighter who was not responding to fires in which people died. If one of these bastions of public trust (police, fire) were violating the trust we had placed in them, the reaction would be strong and swift. And, it is worth noting that this is so egregious a violation, that there is no consideration as to the collateral damage that might be caused by removing him/her from society - for example, hardship to his family, since he is the sole breadwinner. Our hearts would go out to those who were adversely affected, but it would not alter the effect.
We trust root certificate authorities to properly perform the following tasks:
Note: the amount of communication required for a mis-issuance is proportional to the possible effect. For example, if an authorized employee simply misspells a server name of a customer, then notifying the customer, revoking the certificate and reissuing a correct one is probably adequate. However, if unknown individuals were able to issue multiple fraudulent certs, especially for well-known internet sites (like Microsoft, Yahoo or Google), then immediate full and public disclosure is expected in addition to specific outreach to the affected site(s). Any error should be on the side of over-disclosure.
In the case of a compromise of a root certificate authority, Google reserves the right to add that root certificate to the list of root certificates that Google Chrome will not trust, regardless of the settings of the underlying operating system. That decision will be based in part on the response and how proactive the root certificate authority is in regards to discovering and mitigating the incident.
Let’s look at a couple of examples of recent compromises relative to these principles.
In March of 2011, Comodo issued fraudulent certs for a number of well-known internet sites including Microsoft, Yahoo and Google. This was not due to a compromise at Comodo, but rather at an authorized Registration Authority operating on Comodo’s behalf. In that case, Comodo immediately spotted the mis-issuance, revoked the certificates, notified the affected parties, and made a full and public disclosure of what had happened, albeit a week after the event. While the compromise itself cannot be minimized, Comodo mostly acted in a manner consistent with the trust placed in them as a Root CA (earlier disclosure would have been better).
In another case, in July 2011, Diginotar discovered a compromise to their systems, resulting in the mis-issuance of hundreds of certificates. Upon discovery, they chose to quietly revoke the certificates and not announce to anyone the occurrence. Subsequently, a certificate for *.google.com which was issued by their Root CA was found in the wild, and reported by an astute user who was using Chrome as his browser. Chrome has extra checks built in for accessing Google sites, and displayed a warning to the user. The discovery only became public because the user posted his discovery on a public web forum.
This case is very different from the Comodo case, despite a surface similarity. First, Diginotar did not have adequate controls (logging) in place to detect certificate mis-issuance. They only noticed once it was brought to their attention by third parties. They also (apparently) did not have sufficiently adequate controls in place to prevent unauthorized access to their network and systems. It is unclear whether they had adequate audit procedures in place as those depend upon adequate logging, which was not present. In addition to this, once these breaches were discovered, Diginotar did not publicly disclose the breaches, nor did they publish a post-mortem describing what happened, and what was being done to remediate the problem. We do not know if Diginotar notified the organizations for whom there was a mis-issuance, as they have not been forthcoming with that information. Based on which organizations were affected, we strongly believe that they did not, as those organizations would have almost certainly announced the mis-issuance themselves.
As a further indication of their lack of regard for proper security, once their certificates had been removed from browsers (essentially, removing their trusted status), they simply advised end-users to “click-thru” warnings that the browser generates at sites that cannot present a chain of trust to an established Root certificate. Thus, Diginotar was advocating even more bad security practices to circumvent the provisions put into place to protect end-users from their original bad practices. (Note: Diginotar removed the direction to click-thru warnings a couple of days later, and replaced it with a statement that 99.9% of the time the warnings are incorrect, and the certificates can be trusted. They also posted directions on how to download the Diginotar Root certificate and install it manually as a trusted Root certificate.)
These actions by Diginotar raised serious questions about 1) their competence to run a Certificate Authority (of any kind, much less a Root CA), and 2) their interest in protecting the Internet as a whole, over their own interests. For these reasons, we no longer felt that Diginotar deserved the trusted position they once had, and we removed them from that position. We felt that removing their trusted status was warranted for all CAs that Diginotar operates. Further, we intended to block their attempts to restore themselves to a position of trust by creating (or using) alternate CAs.
It is imperative that a user of Google Chrome can be confident that when proper SSL indications are shown in the browser, the user is in fact communicating with the intended site and not an attacker or other man-in-the-middle using a root certificate obtained improperly from a CA. Anything that contravenes this principle, including issuance of certificates for a website to a party other than the legitimate operator of that website, or delegation of authority that results in the issuance of certificates for a website to a party other than the legitimate operator of that website, is a serious violation of trust that will be dealt with in accordance to this policy.
The root certificate policy for Chrome OS is forthcoming.