November 26, 2014

Updating our SSL certificates to SHA-256

Historical

Rob N ★

Alum

This is a technical post. The important points to take away are that if, like most of our customers, you’re using FastMail’s web client with a modern, regularly updated browser like Chrome, Firefox, Internet Explorer or Safari, then everything will be fine. If you’re using an old browser or operating system (including long-unsupported mobile devices like old Nokia or WebOS devices), it may start failing to connect to FastMail during December, and you’ll need to make changes to the settings you use to access FastMail. Read on for details.

For many years the standard algorithm used to sign SSL certificates has been SHA-1. Recently, weaknesses have been exposed in that algorithm which make it unsuitable for encryption work. It’s not broken yet, but it’s reasonable to expect that it will be broken within the next year or two.

A replacement algorithm is available, called SHA-256 (sometimes called SHA-2), and its been the recommended algorithm for new certificates for the last couple of years.

Back in April, we updated our certificates with new ones that used SHA-256. This caused problems for certain older clients that didn’t have support for SHA-256. After some investigation, we reverted to SHA-1 certificates.

Recently Google announced that they would start deprecating SHA-1 support this year. Chrome 40 (currently in testing, due for release in January) will start showing the padlock icon on fastmail.com as “secure, with minor errors”. Crucially, it will no longer display the green “EV” badge.

As a result, we are intending to update our certificates to SHA-256 during December. Its something we wanted to do back in April anyway, as we’d much prefer to proactively support modern security best practice rather than scramble frantically to fix things when breaches are discovered.

Unfortunately, this will cause problems for customers using older browsers. Most desktop browsers should not have any problem, though Windows XP users will need to update to Service Pack 3. Many more obscure devices (notably Nokia and WebOS devices) do not support SHA-256 at all, and will not be able to connect to us securely.

We will be attempting to support a SHA-1 certificate on insecure.fastmail.com and insecure.messagingengine.com, but only if our certificate authority will agree to issue one to us. Once we have that information I’ll update this post.

If you have any questions about this change, please contact support.