Techniques for fighting mis-issuance of TLS certificates
The web has reached the tipping point where encrypted traffic – connections protected by HTTPS, which is HTTP over SSL/TLS – has overtaken unencrypted (HTTP) traffic. There are many reasons for this change, variously called HTTPS Everywhere or Always-On SSL, which we described in a previous FYI blog post. While this move certainly improves the security and privacy of interactions on the web, there still remains the Achilles’ heel of this ecosystem – the problem of mis-issuance of cryptographically legitimate certificates to rogue site operators. This blog post describes recent steps taken to guard against such occurrences, using techniques which can raise the necessary alarms before much harm propagates.
The Achilles’ heel of internet security is the mis-issuance of cryptographically legitimate certificates to rogue site operators.
The entire edifice of SSL/TLS-based security rests on certificates issued to the legitimate operators of websites, so that browser indicators (the secure lock icon, for example) based on various cryptographic checks can reassure users that they are communicating with their intended destination. Mis-issued certificates, whether available through lax procedures at a certificate authority (CA) or by a malignant act, removes that critical trust. A browser’s cryptographic checks cannot distinguish a duly-vetted legitimate server from a man-in-the-middle that has improperly obtained a cryptographically valid certificate. The latter might arise owing to the (mis)placed trust in a compromised root CA embedded in the browser or one issued by a corrupted intermediate CA that is in a legitimate chain of trusted certificates. This is, for example, why Google is reducing trust in SSL certificates issued by Symantec and why even Microsoft is the latest and last browser vendor to no longer going to trust anything issued by the WoSign/StartCom certificate authorities.
Some CAs make mistakes and fix them; some have a habit not well controlling certificate issuance. This seriously damages our trust in a secure internet.
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