Security in distributed systems is a combination of confidentiality, integrity and availability of their components. It mainly targets the communication channels between users and/or processes located in different computers, the access control of users / processes to resources and services, and the management of keys, users and user groups. Distributed systems are more vulnerable to security threats due to several characteristics such as their large scale, the distributed nature of the control, and the remote nature of the access. In addition, an increasing number of distributed applications (such as Internet banking) manipulate sensitive information and have special security requirements. After discussing important security concepts in the Background section, this chapter addresses several important problems that are at the aim of current research in the security of large scale distributed systems: security models (which represent the theoretical foundation for solving security problems), access control (more specific the access control in distributed multi-organizational platforms), secure communication (with emphasis on the secure group communication, which is a hot topic in security research today), security management (especially key management for collaborative environments), secure distributed architectures (which are the blueprints for designing and building security systems), and security environments / frameworks.
