Essay on Ok Ntfs
• What can you do after authentication? • ”The prevention of unauthorized use of a
resource, including the prevention of use of a resource in an unauthorized manner” (ITU-T Recommendation X.800)
AC concepts reference makes monitor request user or represented subject by ”principal” process, method, code…
read, write, delete, create…
object ﬁle, memory, device, process, method, code… protected entity
is granted access (or not)
• Authentication: who made the request? • Authorization: is the subject authorized/ trusted to perform the operation?
• Basic: observe, alter – very abstract, good for modeling …show more content…
Where is each used? (Examples, OS, computer architecture?) Why? (Advantages, disadvantages?)
ACLs vs. Capabilities
File protection, authentication data
• Good for owned objects: can review rights by inspecting objects rights of a subject each reference
• Good: Delegation possible MMU, page table, open ﬁle descriptors, certiﬁcates
• Hard to e.g. revoke all • Expensive to check at
• Hard to see who has with delegation
what access to an object
• Harder to revoke, esp.
• Checking ﬁle ACL for each read/write operation is too expensive (why?)
• Typical solution:
f = open(”ﬁle.txt”,O_RDWR);
‣ check ACL when ﬁle is opened, return ﬁle descriptor which contains rights allowed at opening = capability ‣ check capability at read/write operations
Any problems possible? fail = write(f, buffer, size);
But who sets access rights?
• Deﬁne an owner of each object • Let owner set access rights for objects at his/her discretion
Discretionary AC (DAC)
• Like standard ﬁle protection
Any problems possible?
Mandatory AC (MAC)
• System-wide access control policy decides • Avoids mistakes (or centralizes