Beginning January Google will start using full page warnings in
Chrome when the browser encounters sites using TLS/SSL or digital certificates
signed with the aging SHA-1 hashing algorithm.
The move will take effect once users update to Chrome 56, which is due for release around the end of January 2017. From that date, Chrome users will begin to see an interstitial or full page warning, that likely will warn them against proceeding. This will have a major impact on traffic for sites that still use SHA-1 signed TSL/SSL certificates.
Foreseeing a slow migration, Google started winding down support for SHA-1 in 2014 after research showed it would soon be cheap to launch a collision attack against SHA-1 and forge certificates, meaning any well-resourced attacker, such as a government agency or criminal group, could realistically impersonate any HTTPS site using a certificate signed with the algorithm.
“To protect users from such attacks, Chrome will stop trusting certificates that use the SHA-1 algorithm, and visiting a site using such a certificate will result in an interstitial warning,” said Andrew Whalley, a security engineer on Google’s Chrome security team.
This could pose a problem for potentially hundreds of thousands of websites that haven’t prepared for browser makers abandoning SHA-1. Microsoft will begin blocking SHA-1 certificates in February 2017 for both the Edge browser and Internet Explorer. Firefox will flag an “untrusted connection” when encountering a SHA-1 certificate from “early 2017”.
Security firm Netcraft in October found one million actively used SSL certificates signed with SHA-1.
Security firm Venafi Labs estimates that 35 percent of websites are still using SHA-1 certificates. Most major websites have switched, but the company says many websites still haven’t.
Google’s announcement on Tuesday sets a concrete deadline for website operators to switch to SHA-256 signed certificates or other so-called SHA-2 certificates. Google’s deadline is important for any site due to the sheer number of people who rely on Chrome to do things on the web.
Whalley urged website operators to check the Qualys SSL server test to asses their web server setup for any SHA-1 certificates and “immediately contact their CA for a SHA-256 based replacement if any are found”.
He also warned enterprise, which may still use these certificates for internal operations, to ensure there is no conflict with Google’s extended support of SHA-1.
“As Chrome makes use of certificate validation libraries provided by the host OS when possible, this option will have no effect if the underlying cryptographic library disables support for SHA-1 certificates; at that point, they will be unconditionally blocked. We may also remove support before 2019 if there is a serious cryptographic break of SHA-1.
Enterprises are encouraged to make every effort to stop using SHA-1 certificates as soon as possible and to consult with their security team before enabling the policy,” said Whalley.