Whenever I try to open this site, my Firefox displays a warning:

The owner of linearalgebras.com has configured their website improperly.

To protect your information from being stolen, Firefox has not connected to this website.linearalgebras.com uses an invalid security certificate. The certificate is only valid for the following names: *.github.com, github.com, *.github.io Error code: SSL_ERROR_BAD_CERT_DOMAIN

How can I check if it's safe for me to access the site?

Any help would be appreciated.

  • 1
    Just connect over HTTP? – Luke Park Aug 3 '16 at 22:41

It is (kind of) a misconfiguration.

The site is hosted on GitHub Pages and it does not have a certificate configured for the linearalgebras.com domain. GitHub does not seem to offer the option to configure a certificate for custom domains (although it can be configured with CloudFlare).

As GitHub does not block HTTPS connections coming to its addresses and seems to use the same infrastructure for its core services as well as GitHub Pages, any connection coming to the servers will get a certificate for GitHub-owned domains.

That said, there is no security risk in accepting the GitHub's certificate for linearalgebras.com and using the site over HTTPS. The connection would be encrypted and data could not be intercepted by a 3rd party. GitHub as a hosting provider would be able to access the data anyway.

Side note: if you try opening (the address DNS resolves to, but without SNI), you'll see the GitHub's 404.

  • 1
    Great book by the way – Verbal Kint Aug 4 '16 at 13:51

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