Authentication-Advance Operating System-Lecture Slides, Slides of Advanced Operating Systems

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Lecture No.

Overview of today’s lecture

 User authentication  Password based authentication  UNIX password scheme  One-time password schemes  Challenge response authentication  Biometrics and other authentication schemes  Access control and authorization  Access control matrix

Authentication (2)

 Unix password security Encrypt passwords  One time passwords Lamport’s clever scheme (Read Tanenbaum for details)  Challenge-Response based authentication Used in PPP and many other applications

Authentication alternatives

 Badge or key Does not have to be kept secret. usually some sort of picture ID worn on jacket (e.g., at military bases)  Should not be forgeable or copy-able  Can be stolen, but the owner should know if it is  (but what to do? If you issue another, how to invalidate old?)  This is similar to the notion of a “capability” that we’ll see later

Access control

 Context  System knows who the user is  User has entered a name and password, or other info  Access requests pass through gatekeeper  OS must be designed so monitor cannot be bypassed ? Resource User process Decide whether user can apply operation to resource Reference monitor

Access control matrix [Lampson]

File 1 File 2 File 3 (^) … File n User 1 (^) read write - - read User 2 (^) write write write - - User 3 (^) - - - read read … User m (^) read write read write read Subjects Objects