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.