Security is essential to enable the Internet of Things (IoT). Key security measures that work well on the traditional Internet, however, do not necessarily adapt well to the IoT. Specifically, authentication and/or authorization based on certificates provided by certificate authorities (CAs) cannot, in current form, scale to the expected 50 billion devices. And widely used encryption technologies for the Internet require too much energy for resource-constrained devices. This paper describes a secure network architecture with key distribution mechanisms using local, automated authorization entities. The architecture provides security guarantees while addressing IoT-related issues including resource constraints. For evaluation, we show that the architecture's overhead scales at a significantly slower rate than widely used SSL/TLS and works well with resource-constrained devices.