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Verifying TLS Certificates
Checking the Box
Most websites deliver their content in encrypted form, as indicated by HTTPS at the start of the URL. The web browser only accepts data from the requested server after it has verified its identity by a valid certificate. After that, the web content appears in the browser and you can start browsing. If it discovers security issues, the browser issues a warning. You can get a certificate warning for many reasons: an expiry date in the past, a self-signed certificate, an unknown issuer, or a missing intermediate certificate.
If the web browser does not give you a clear explanation of the cause, or if you are interested in the certificate chain, the certigo [1] command-line tool can be a big help. The utility accesses the web server like a browser, reports on the certificates it receives, and provides further information about the type of encryption. Figure 1 shows how certigo checks a website and confirms with green highlighting that all the certificates are valid and no intermediate certificates are missing.
Figure 1: The certigo utility checks the entire chain – from the server certificate to the certificate authority – and color codes the results.
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