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Google Spat With Chinese Firm Highlights Digital Certificate Security Challenges

Chrome will no longer trust certs issued by CNNIC following recent snafu, and Mozilla Firefox will revoke certs issued by the Chinese authority before April 1.

A decision by Google to drop a Chinese root certificate authority (CA) for its role in the recent issuance of unauthorized digital certificates for several Google domains underscores yet again the brittle nature of the Internet trust model. Mozilla also announced that it will take action against the CA.

Google yesterday said that its Chrome browser would no longer recognize certificates issued by China Internet Network Information Center (CNNIC). The change will take effect in a future Chrome update, according to Google.

"For a limited time we will allow CNNIC’s existing certificates to continue to be marked as trusted in Chrome, through the use of a publicly disclosed whitelist," Google security engineer Adam Langley said in a blog update this week.

CNNIC will have an opportunity to apply for re-inclusion as a trusted certificate authority for Chrome in future, once the company has implemented suitable technical and procedural controls, Langley said.

Mozilla, meanwhile, also said it is taking action against CNNIC for the errant certificates. But the browser maker stopped short of completely removing CNNIC's certificates from its root store. Instead, Mozilla said it would update Firefox so the browser will not trust any certificate issued before April 1, 2015 by CNNIC's roots. Like Google, Mozilla also said CNNIC could apply for full inclusion once it completes certain additional steps to improve its processes.

Google's move evoked sharp criticism from CNNIC. "The decision that Google has made is unacceptable and unintelligible to CNNIC," the company said in a statement. "For the users that CNNIC has already issued the certificates to, we guarantee that your lawful rights and interests will not be affected," the company said, without specifying how. 

Both browser makers were responding to a recent incident where a CNNIC customer, Egypt-based MCS Holdings, accidentally issued unauthorized digital certificates for several Google domains using an unrestricted intermediary certificate authority granted to it improperly by CNNIC. 

Digital certificates are a fundamental component of the Internet trust model. Web browsers rely on digital certificates to authenticate websites and to encrypt communications between websites and browsers. Websites use certificates like those issued by a CA like CNNIC to basically vouch for their identity so browsers know to trust them.

The unauthorized certificates that were issued by MCS potentially could have let someone set up fake Google domains and intercept communications between and to the domains. "CNNIC is included in all major root stores and so the [wrongly issued] certificates would be trusted by almost all browsers and operating systems," Langley wrote in a blog post last week explaining the issue.

The problem resulted from MCS's mishandling of an unrestricted intermediate certificate that Google and Mozilla say CNNIC should never have issued to MCS in the first place.

"We have concluded that CNNIC’s behavior in issuing an unconstrained intermediate certificate to a company with no documented PKI practices and with no oversight of how the private key was stored or controlled was an 'egregious practice,'" Mozilla wrote in its bog.

Google’s decision to pull CNNIC's certificates from its root store makes sense, says Dan Kaminsky, DNS expert and chief scientist at security vendor White Ops.

"Managing certs is an extraordinarily high-touch business with very serious requirements for correctness," Kaminsky says. "Mistakes can be very painful to correct, as revocation does not work in practice."

Certificate authorities like CNNIC get paid to do a job, and if they can't do it, somebody else needs to get paid to do it, he says. "This is likely to further moves by browser vendors to be more involved managing and overseeing the global population of certificates."

Andrew Sullivan, fellow at Internet performance company Dyn, says the entire episode highlights the somewhat fragile nature of trust on the Internet.  "CAs are never supposed to screw up," he says. As an entity authorized to issue the certificates that websites use to authenticate their identity on the Web, a CA is in a position of enormous responsibility.

"The entire web of trust depends on the CA never screwing up because if they do we are all hosed," Sullivan says.

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