Content-based publish/subscribe systems offer an interaction scheme that is appropriate for a variety of large-scale dynamic applications. However, widespread use of these systems is hindered by a lack of suitable security services. In this paper, we present scalable solutions for confidentiality, integrity, and authentication for these systems. We also provide verifiable usage-based accounting services, which are required for e-commerce and e-business applications that use publish/subscribe systems. Our solutions are applicable in a setting where publishers and subscribers may not trust the publish/subscribe infrastructure.