This article presents an overview of the security mechanisms in the NDN architecture that have been developed over the past several years. NDN changes the network communication model from the delivery of packets to hosts identified by IP addresses to the retrieval of named and secured data packets. Consequently, NDN also fundamentally changes the approaches to network security. Making named data the centerpiece of the architecture leads to a new security framework that secures data directly, and uses name semantics to enable applications to reason about security and to automate the use of cryptographic keys. In this article, we introduce NDN's approaches to security bootstrapping, data authenticity, confidentiality, and availability.