  Although TLS is used on a daily basis by many critical applications, the
public-key infrastructure that it relies on still lacks an adequate revocation
mechanism. An ideal revocation mechanism should be inexpensive, efficient,
secure, and privacy-preserving. Moreover, rising trends in pervasive encryption
pose new scalability challenges that a modern revocation system should address.
In this paper, we investigate how network nodes can deliver
certificate-validity information to clients. We present RITM, a framework in
which middleboxes (as opposed to clients, servers, or certification
authorities) store revocation-related data. RITM provides a secure
revocation-checking mechanism that preserves user privacy. We also propose to
take advantage of content-delivery networks (CDNs) and argue that they would
constitute a fast and cost-effective way to disseminate revocations.
Additionally, RITM keeps certification authorities accountable for the
revocations that they have issued, and it minimizes overhead at clients and
servers, as they have to neither store nor download any messages. We also
describe feasible deployment models and present an evaluation of RITM to
demonstrate its feasibility and benefits in a real-world deployment.
