Microsoft is considering adding public-key pinning–an important defense against man-in-the-middle attacks–to Internet Explorer.
The feature is designed to help protect users against the types of MITM attacks that rely on forged certificates, which comprise a large portion of those attacks. Attackers use forged or stolen certificates to trick victims’ browsers into trusting a malicious site that the attacker controls. Public-key pinning helps prevent those attacks by binding a set of public keys issued by a trusted certificate authority to a specific domain. With that defense in place, if the user visits the site and is presented with a key that’s not part of the pinned set, the browser will reject the secure connection.
Public-key pinning as an extension to HTTP is laid out in an Internet-Draft submitted to the IETF by a group of Google security engineers in October. The
draft makes it clear that in order for the system to work, site operators must be up to the task.
