Revocation of Access Rights

Are these to be performed

• Immediately or after a delay
• For all users or a selective group
• All rights or partial rights
• Temporary or permanent

Remove access rights for an object - given to a user/domain

Easy with global table or access list - search list for object and remove entry

Capabilities are distributed throughout the system - must be found and destroyed - difficult

• Expiry Time : capabilities expire after a time and new must be requested - this is refused if rights have been revoked
• Back pointers : objects maintain pointers to all capabilities issued - costly to implement, particularly if capabilities are passed around as parameters
• Indirect Capabilities : capability points to table entry which points to object - Invalidate entry to revoke capability - No selective revocation
• Keys : capability contains encrypted key checked by object - change key in object to revoke capability - No selective revocation