CAPS: Smoothly Transitioning to a More Resilient Web PKI

Many recent proposals to increase the resilience of the Web PKI against misbehaving CAs face significant obstacles to deployment. These hurdles include (1) the requirement of drastic changes to the existing PKI players and their interactions, (2) the lack of signaling mechanisms to protect against downgrade attacks, (3) the lack of an incremental deployment strategy, and (4) the use of inflexible mechanisms that hinder recovery from misconfiguration or from the loss or compromise of private keys. As a result, few of these proposals have seen widespread deployment, despite their promise of a more secure Web PKI. To address these roadblocks, we propose Certificates with Automated Policies and Signaling (CAPS), a system that leverages the infrastructure of the existing Web PKI to overcome the aforementioned hurdles. CAPS offers a seamless and secure transition away from today’s insecure Web PKI and towards present and future proposals to improve the Web PKI. Crucially, with CAPS, domains can take simple steps to protect themselves from MITM attacks in the presence of one or more misbehaving CAs, and yet the interaction between domains and CAs remains fundamentally the same. We implement CAPS and show that it adds at most 5% to connection establishment latency.