Notes for November 30, 2000
- Greetings and Felicitations!
- Discuss project
- Puzzle of the day
- Capability-based addressing: show picture of accessing object
- Show process limiting access by not inheriting all parent's
- Revocation: use of a global descriptor table
- MULTICS ring mechanism
- MULTICS rings: used for both data and procedures; rights are
- (b1, b2) access bracket - can
freely; (b3, b4) call bracket - can
through gate; so if a's access bracket is (32,35) and its call
is (36,39), then assuming permission mode (REWA) allows access, a
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
rings 40-63: cannot access a
- 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
- Lock and Key
- Associate with each object a lock; associate with each
process that has access to object a key (it's a cross between ACLs and
- Example: use crypto (Gifford). X object enciphered with key
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
process with access to any of the Di's can access the
AND-Access: need all n deciphering functions to get K:
- Mandatory vs. Discretionary;
- security levels
- Bell-LaPadula Model
- Simple Security Property: no reads up
- Star Property: no writes down
- Discretionary Security Property: if mandatory controls say it's
okay, check discretionary controls.
- Basic Security Theorem: A system is secure if its initial state is
secure and no action violates the above rules.
- Lattice Model
- Set of classes SC is a partially ordered set under relation
with GLB, LUB
- Note: SUBSET is reflexive, transitive, antisymmetric
- Application to MLS: forms a lattice with elements being the
Cartesian product of the linear lattice of levels and the subset lattics
- 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
The Eskimo stabbed himself with an icicle. He died of cold cuts.
In his dessert list, a San Antonio restaurateur suggests, "Remember
There was an advice-to-the-lovelorn editor who insisted, "If at
first you don't succeed, try a little ardor."
The commuter's Volkswagen broke down once too often. So he consigned it
to the Old Volks Home.
The wise old crow perched himself on a telephone wire. He wanted to
make a long-distance caw.
A talkative musician couldn't hold a job. Every time he opened his
mouth, he put his flute in it.
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."
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
A critic declared that he always praised the first show of a new
theatrical season. "Who am I," he asked, "to stone the
Egotist: a person who's always me-deep in conversation.
"It's raining cats and dogs," one man remarked. "I
know," said another. "I just stepped into a poodle."
An eccentric bachelor passed away and left a nephew nothing but 392
clocks. The nephew is now busy winding up the estate.
The baseball pitcher with a sore arm was in the throws of agony.
Office: 3059 Engineering Unit II
Phone: +1 (530) 752-8060
Fax: +1 (530) 752-4767
Copyright Matt Bishop, 2000.
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presented in this course through any medium, including lecture or print.
Page last modified on 11/30/2000