02 July 2015

Do you know which CAs can issue SSL/TLS certificates trusted by your PC or phone?

Most PC and phone users are blissfully unaware that their PC or phone have a very long list of trusted root CAs, certificate authorities that can sign SSL/TLS or code signing certificates that will be accepted at face value. Those root CA lists are regularly updated, most recently all Windows PCs silently got a bunch of new trusted root CAs from the Chinese government, India CCA, etc.

In other words: a few hundred organizations that you have probably never heard of, and a few thousand organizations trusted by them, can issue certificates that is trusted by your web browser, mail client, and used for signing software. Any of them can issue a SSL certificate for any web property, and sometimes they do issue certificates to the wrong party. When a certificate is issued to someone else than the legitimate site-owner, it opens up for man-in-the-middle attacks where an unknown third-party can intercept and modify communication between a web browser and web server.

To reduce the risk of getting man-in-the-middle'd by someone who got a certificate from one of those CAs (or the thousands of intermediates trusted by them), it is a good idea to regularly trim the list of trusted root CAs on your PC or phone so only the ones you really need are trusted. It is relatively easy to update the list of trusted root CAs on a PC or phone, the following two infographics shows how to trim trusted root CAs on Windows and Android, respectively.

Windows


Android




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