PBDM: A Flexible Delegation Model in RBAC

1. PBDM: A Flexible Delegation Model in RBAC Xinwen Zhang, Sejong Oh George Mason University Ravi Sandhu George Mason University and NSD Security

2. Outline • Motivations • Related Works • PBDM0: user-to-user delegation • PBDM1: user-to-user delegation • PBDM2: role-to-role delegation • Conclusions and future work

3. Motivations • Permission level delegations are needed in many cases:

4. Motivations(cont’d) • User-to-user delegations • John delegates some of his permissions to Jenny when he is out of town • Role-to-role delegations • A professor can delegate “check-email” permission to a TA • Multi-step delegation and revocation • Jenny can delegate some permissions from John to Jim

5. Related Works • RBDM0: • E.Barka et al, NISSC 2000, ACSAC 2000 • A delegation framework • User-to-user delegation • Role-level delegation • RDM2000 • L.Zhang et al, SACMAT 2002 • Role-level delegation • Multi-step delegation

6. PBDM0 • Permission-based Delegation Model • A user-to-user delegation model • John creates a temporary delegation role D1. • John assigns the permission “change_schedule" to D1 with permission-role assignment and role PE to D1 with role-role assignment. • John assigns Jenny to D1 with user-role assignment.

7. PBDM0 • RR: regular roles • DTR: delegation roles Controlled by security administrator: • UAR: user-regular role assignment • PAR: permission-regular role assignment Controlled by individual user: • UAD: user-delegation role assignment • PAD: permission-delegation role assignment

8. PBDM0

9. PBDM1 • Problems in PBDM0: • A user can create delegation role by his discretion. Invalid permission flow can happen with malicious user. There reason is that there is no security administrator involvement in delegation. • Cannot support role-to-role delegation, since delegation role cannot be assigned to a regular role. • PBDM1: • Extension from PBDM0 • Permissions of a role are separated into two parts: regular and delegatable. • Only delegatable permissions can be used to create delegation roles. • User-to-user delegation

10. PBDM1 • RR: regular roles • DBR: delegatable roles • DTR: delegation roles • One-to-one map between RR and DBR

11. PBDM1

12. PBDM1 • UAR, UAB, PAR, and PAB are managed by security administrator. • UAD and PAD are managed by individual user. • Revocation options: • By a user: • Remove a user from delegatees, that is, revoke the user-delegation role assignment. • Remove one or more pieces of permissions from delegation role. • Revoke delegation role. • By a security administrator: • Remove one or more pieces of permission from a delegatable role to its regular role. • Revoke a user from regular role and delegatable role.

13. PBDM2 • Extension from PBDM1 • A role-to-role delegation model • A role is separated into three layers: • Regular role(RR): permissions cannot be delegated. • Fixed delegatable role(FDBR): permission can be delegated. • Temporal delegatable role(TDBR): inherit permissions from delegation roles with role-role assignment(RAD). • Delegation roles (DTR) are assigned to temporal delegatable role • Since there is no role hierarchy with TDBR, illegal permission flow will not happen.

14. PBDM2 • A delegation role D3 owned by PL’ and delegated to QE”: • Create a temporary delegation role D3 • assign the permission “change_schedule" to D3 • assign role PE’ to D3 • Assign D3 to QE”

15. PBDM2 • RR, FDBR, TDBR, DTR • RRH, FDBRH • UAR, UAFB, UATB • PAR, PAFB, PADB • RAD: delegation role-temporal delegatable role assignment

16. PBDM2 • Revocation options: • Remove one or more pieces of permissions from delegation role. • Revoke delegation role owned by a fixed delegatable role. • Remove one or more pieces of permission from a fixed delegatable role to its regular role.

17. Conclusions and Future Work • Conclusions: • Present a permission-based delegation model family, PBDM0, PBDM1, and PBDM2. • Support user-to-user and role-to-role delegation • Support multi-step delegation • Support multi-option revocation • Flexible delegation administration • Future work: • Constraints in RBAC delegation, such as separation of duty • Delegation management in decentralized environment