Security services based on cryptographic mechanisms assume keys to be distributed prior to secure communications. The secure management of these keys is one of the most critical elements when integrating cryptographic functions into a system, since any security concept will be ineffective if the key management is weak. This work approaches the problem of key management in a modular and hierarchical manner. It discusses key management security requirements, deals with generic key management concepts and design criteria, describes key management services and building blocks, as well as key management facilities, key management units, and their interrelationship.>