TLS Connection Validation by Web Browsers: Why do Web Browsers Still Not Agree?

The TLS protocol is the primary technology used for securing web transactions. It is based on X.509 certificates that are used for binding the identity of web servers' owners to their public keys. Web browsers perform the validation of X.509 certificates on behalf of Web users. Our previous research in 2009 showed that the validation process of Web browsers is inconsistent and flawed. We showed how this situation might have a negative impact on Web users. From 2009 until now, many new X.509 related standards have been created or updated. In this paper, we performed an increased set of experiments over our 2009 study in order to highlight the improvements and/or regressions in Web browsers' behaviours.