Google joins Mozilla, Microsoft in pushing for early SHA-1 crypto cutoff

The browser makers are worried about research that shows SHA-1 is even weaker than previously believed

Google is considering banning certificates signed with the SHA-1 cryptographic function in Google Chrome starting Jul. 1. This follows similar announcements from Mozilla and Microsoft over the past two months.

The browser vendors had previously decided to stop trusting SHA-1-signed certificates presented by HTTPS websites on Jan. 1, 2017, a year after certificate authorities are supposed to stop issuing new ones.

However, due to recent research showing that SHA-1 is weaker than previously believed, Mozilla, Microsoft and now Google are all considering bringing the deadline forward by six months.

"In line with Microsoft Edge and Mozilla Firefox, the target date for this step is January 1, 2017, but we are considering moving it earlier to July 1, 2016 in light of ongoing research," Google Chrome team members Lucas Garron and David Benjamin said Friday in a blog post. "We therefore urge sites to replace any remaining SHA-1 certificates as soon as possible."

Until then, starting with Chrome version 48, which is expected to land early next year, the browser will display errors if the certificates served by websites have SHA-1 signatures and were issued after Jan. 1, 2016. That's because public certificate authorities (CAs) are not supposed to issue new SHA-1-signed certificate after that date.

Later in the year, Chrome might be updated to apply the same treatment to website certificates that chain back to intermediary certificates signed with SHA-1.

Websites like Facebook and those protected by CloudFlare have implemented a SHA-1 fallback mechanism. Both companies have argued that there are millions of people in developing countries that still use browsers and operating systems that do not support SHA-2, the replacement function for SHA-1, and will therefore be cut off from encrypted websites that move to SHA-2 certificates.

The companies also want CAs to continue to issue SHA-1 certificates into 2016, but only to website owners that can prove that they serve SHA-2 certificates to modern browsers and fall back to SHA-1 only for older clients.

The advent of cheap cloud computing in recent years has signed the death warrant for SHA-1, a hashing algorithm that dates back to 1995 and is known to be vulnerable to computationally intensive collision attacks that could result in signature and therefore certificate forgery.

While the U.S. National Institute of Standards and Technology has long mandated that federal agencies should move away from SHA-1, the SSL industry has lagged behind, to the point that in September almost one in three of the most popular 145,000 HTTPS-enabled websites were still using a SHA-1 certificate. The percentage is now around 15 percent.

Three years ago, researchers estimated that a practical attack against SHA-1 would cost $700,000 using commercial cloud computing services by 2015 and $173,000 by 2018.

However, in October, a group of researchers presented a new way to break SHA-1 that is expected to lower the cost of attacks more quickly than previously anticipated. It is this research that has browser makers worried and prompted them to consider an early cutoff date for SHA-1 certificates.

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