Notes for February 5, 1997

  1. Hello
    1. Homework grades will be mailed back soon; grading programs is taking a bit longer than we thought
    2. No homework; study for exam and/or work on project
  2. Puzzle of the day
    1. Key point: pornographic pictures or pirated software can be left behind in a "." directory that the remove won't delete.
  3. Capabilities
    1. Capability-based addressing: show picture of accessing object
    2. Show process limiting access by not inheriting all parent's capabilities
    3. Revocation: use of a global descriptor table
  4. Lock and Key
    1. Associate with each object a lock; associate with each process that has access to object a key (it's a cross between ACLs and C-Lists)
    2. Example: use crypto (Gifford). X object enciphered with key K. Associate an opener R with X. Then:
      OR-Access: K can be recovered with any Di in a list of n deciphering transformations, so
      R = (E1(K), E2(K), ..., En(K)) and any process with access to any of the Di's can access the file
      AND-Access: need all n deciphering functions to get K: R = E1(E2(...En(K)...))
  5. MULTICS ring mechanism
    1. MULTICS rings: used for both data and procedures; rights are REWA
    2. (b1, b2) access bracket - can access freely; (b3, b4) call bracket - can call segment through gate; so if a's access bracket is (32,35) and its call bracket is (36,39), then assuming permission mode (REWA) allows access, a procedure in:
      rings 0-31: can access a, but ring-crossing fault occurs
      rings 32-35: can access a, no ring-crossing fault
      rings 36-39: can access a, provided a valid gate is used as an entry point
      rings 40-63: cannot access a
    3. If the procedure is accessing a data segment d, no call bracket allowed; given the above, assuming permission mode (REWA) allows access, a procedure in:
      rings 0-32: can access d
      rings 33-35: can access d, but cannot write to it (W or A)
      rings 36-63: cannot access d
  6. Mandatory vs. Discretionary;
    1. security levels
    2. categories
  7. Bell-LaPadula Model
    1. Simple Security Property: no reads up
    2. Star Property: no writes down
    3. Discretionary Security Property: if mandatory controls say it's okay, check discretionary controls.

You can also see this document as a Binhex Framemaker version 5 document, Postscript document, or a plain ASCII text document.
Send email to

Department of Computer Science
University of California at Davis
Davis, CA 95616-8562

Page last modified on 2/8/97