Iolus is a novel framework for scalable secure multicasting. The paper discusses the differences between securing unicast and multicast communications, highlighting that multicast security is fundamentally different due to its group-based nature. This leads to scalability challenges, as changes in group membership affect all members. Iolus addresses these issues by using a secure distribution tree, where each subgroup is independent and can manage its own keying material. This approach allows for efficient key management and reduces the impact of membership changes on the entire group. The framework is designed to be flexible, supporting various security objectives and can be used for both direct secure multicasting and as a group key management service for other applications. The paper describes the architecture and operation of Iolus, including its use in secure multicast data delivery and as a keying service for video-conferencing applications. It also discusses deployment issues, performance results, and related approaches to multicast security. The framework is shown to be effective in handling scalability and security challenges in multicast communications.Iolus is a novel framework for scalable secure multicasting. The paper discusses the differences between securing unicast and multicast communications, highlighting that multicast security is fundamentally different due to its group-based nature. This leads to scalability challenges, as changes in group membership affect all members. Iolus addresses these issues by using a secure distribution tree, where each subgroup is independent and can manage its own keying material. This approach allows for efficient key management and reduces the impact of membership changes on the entire group. The framework is designed to be flexible, supporting various security objectives and can be used for both direct secure multicasting and as a group key management service for other applications. The paper describes the architecture and operation of Iolus, including its use in secure multicast data delivery and as a keying service for video-conferencing applications. It also discusses deployment issues, performance results, and related approaches to multicast security. The framework is shown to be effective in handling scalability and security challenges in multicast communications.