Notes for November 30, 2000

1. Greetings and Felicitations!
   1. Discuss project
2. Puzzle of the day
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. MULTICS ring mechanism
   1. MULTICS rings: used for both data and procedures; rights are REWA
   2. (b₁, b₂) access bracket - can access freely; (b_{3, 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. c. 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
5. 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 D_i in a list of n deciphering transformations, so
      R = (E₁(K), E₂(K), ..., E_n(K)) and any process with access to any of the D_i's can access the file
      AND-Access: need all n deciphering functions to get K: R = E₁(E₂(...E_n(K)...))
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.
   4. Basic Security Theorem: A system is secure if its initial state is secure and no action violates the above rules.
8. Lattice Model
   1. Set of classes SC is a partially ordered set under relation SUBSET with GLB, LUB
   2. Note: SUBSET is reflexive, transitive, antisymmetric
   3. Application to MLS: forms a lattice with elements being the Cartesian product of the linear lattice of levels and the subset lattics of categories
   4. Examples: (A, C) DOMINATES (A', C') iff A <= A' and C SUBSET C';
      LUB((A, C), (A', C')) = (max(A, A'), C UNION C')
      GLB((A, C), (A', C')) = (min(A, A'), C INTERSECTION C')

Puzzle of the Day

Computer security experts seem to like puns. So if you want to talk as a computer security expert, you must be able to inject bad puns into your conversation. To get you started, here are some puns from what the Book of Lists 2 calls the world's worst puns. Consider yourselves armed (or forewarned)!

1. The Eskimo stabbed himself with an icicle. He died of cold cuts.
2. In his dessert list, a San Antonio restaurateur suggests, "Remember the alamode!"
3. There was an advice-to-the-lovelorn editor who insisted, "If at first you don't succeed, try a little ardor."
4. The commuter's Volkswagen broke down once too often. So he consigned it to the Old Volks Home.
5. The wise old crow perched himself on a telephone wire. He wanted to make a long-distance caw.
6. A talkative musician couldn't hold a job. Every time he opened his mouth, he put his flute in it.
7. A farmer with relatives in East Germany heard that a food package he had sent had never arrived. Optimistically, he assured them, "Cheer up! The wurst is yet to come."
8. When the promoter of a big flower show was told that a postponement was necessary because the exhibits could not be installed on time, he explained to his backers, "We were simply caught with our plants down."
9. A critic declared that he always praised the first show of a new theatrical season. "Who am I," he asked, "to stone the first cast?"
10. Egotist: a person who's always me-deep in conversation.
11. "It's raining cats and dogs," one man remarked. "I know," said another. "I just stepped into a poodle."
12. An eccentric bachelor passed away and left a nephew nothing but 392 clocks. The nephew is now busy winding up the estate.
13. The baseball pitcher with a sore arm was in the throws of agony.

Matt Bishop Office: 3059 Engineering Unit II Phone: +1 (530) 752-8060 Fax: +1 (530) 752-4767 Email: bishop@cs.ucdavis.edu

Copyright Matt Bishop, 2000. All federal and state copyrights reserved for all original material presented in this course through any medium, including lecture or print.