Quantum key distribution (QKD) enables two remote parties to share a common random binary key that is unknown to a potential eavesdropper. QKD networks based on trusted nodes (QKD nodes) have been widely adopted to enlarge the key distribution distance and enrich QKD-based applications. The trustworthiness of a QKD node is fundamental to ensure the overall security in a QKD network. This Recommendation provides guidance for the secure implementation and operation of QKD nodes in QKD networks. This Recommendation identifies security threats, provides security requirements for QKD nodes and provides specific techniques to meet the requirements.