Security Models for Authorization, Delegation and Accountability

This dissertation, "Security Models for Authorization, Delegation and Accountability" by W C, Lui, 雷永祥, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Security Models for Authorization, Delegation and Accountability Submitted by Lui Wing Cheung for the degree of Doctor of Philosophy at the University of Hong Kong in August 2005 Role Based Access Control (RBAC) is an important access control technology. To support the principle of the least privilege in RBAC, a user should activate one or more roles in order to exercise the associated permission. However, the importance of managing the process of role activation has been neglected in existing studies. In this thesis, various approaches to manage the role activation process are proposed. The decentralized approach provides the most flexible and decentralized way to specify and enforce dynamic constraints. However, it cannot be supported by most existing RBAC systems. Therefore, an access control model and an authorization process are proposed to support the decentralized management of role activation policies in organizations. Another approach to decentralize the security management process is the delegation of authority. The delegation certificate is a popular technique for handling chained delega- tion. However, the authorization verification process is inefficient in handling long delegation chains. Proxy signature provides an alternative way for delegation which supports more effi- cient verification of authorization. However, only one level of delegation is supported. In this 2thesis, Kim et al.'s proxy signature, which only handles one level of delegation, is extended to support efficient verification for delegation chains. The proposed scheme is analyzed in terms of security and efficiency. Although delegation certificates and proxy signatures support the decentralized manage- ment of access rights in organizations without the need for a centralized server to mediate every delegation operation, they do not allow the permission to be delegated in a flexible way. Therefore, a new delegation model (delegation with supervision) is proposed to allow the var- ious delegators in a delegation chain to perform supervision on the delegate when exercising the delegated permission. The ways to support delegation with supervision are described by extending the delegation certificate and a proxy signature scheme. One important issue in delegation is accountability, which is neglected in traditional del- egation paradigms. In this thesis, the notion of accountability in delegation is introduced to associate an action with the users who should be legally/socially responsible/liable for the consequence of an action. To provide a context for discussion, a new accountability model for organizations is proposed. The accountability services may be provided by individual applica- tion or shared by multiple applications. This provides a flexible way to support accountability in organizations. Delegation certificates and proxy signatures require the presence of a trusted system to mediate access and enforce the security policy. Proxy cryptography supports decryption del- egation without the need for such a trusted component. To support a more decentralized alternative for delegation, a decryption delegation model is proposed to allow the users to delegate the permission to decipher encrypted documents (with a certain classification and 3time of receipt) without revealing the delegator's private key. The decryption delegation and re-encryption process at the receiver side is transp