Notes for November 30, 2000

1.	Greetings and Felicitations!

a.	Discuss project

2.	Puzzle of the day

3.	Capabilities

a.	Capability-based addressing: show picture of accessing object

b.	Show  process limiting access by not inheriting all parent's capabilities

c.	Revocation: use of a global descriptor table

4.	MULTICS ring mechanism

a.	MULTICS rings:  used for both data and procedures; rights are REWA

b.	 (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

c.	If the procedure is accessing a data segment d, no call bracket allowed; given the above, assuming permis-
sion 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

a.	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)

b.	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)...))

6.	Mandatory vs. Discretionary;

a.	security levels

b.	categories

7.	Bell-LaPadula Model

a.	Simple Security Property: no reads up

b.	Star Property: no writes down

c.	Discretionary Security Property: if mandatory controls say it's okay, check discretionary controls.

d.	Basic Security Theorem: A system is secure if its initial state is secure and no action violates the above rules.

8.	Lattice Model

a.	Set of classes SC is a partially ordered set under relation  with GLB (f), LUB ()

b.	Note:  is reflexive, transitive, antisymmetric

c.	Application to MLS: forms a lattice with elements being the Cartesian product of the linear lattice of levels 
and the subset lattics of categories

d.	Examples: (A, C)  (A', C') iff A  A' and C � C';
(A, C)  (A', C") = (max(A, A'), C � C')
(A, C) f (A', C') = (min(A, A'), C � 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.