Publish-subscribe protocols offer a unique means of data distribution, that has many applications for distributed systems. These protocols enable message delivery based on subscription rather than specific addressing; meaning a message is addressed by a subject string rather than to a specific recipient. Recipients may then subscribe to subjects they are interested in receiving using a variety of parameters, and receive these messages immediately without having to poll for them. This format is

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... natural match for anonymous delivery systems: systems that enable users to send messages without revealing their identity. These systems are an area of great interest, ranging from messaging relays like Tor, to publication systems like FreeHaven. However, existing systems do not allow delivery based on topics, a mechanism which is a natural match for anonymous communication since it is not addressed based on identity. We concretely describe the properties of and propose a system that allows publish-subscribe based delivery, while protecting the identities of both the publishers and subscribers from each other, from outside parties, and from entities that handle the implementation of the system.