Notes for February 7, 1997
Homework grades will be mailed back as soon as we're done ... programs
are the bottleneck. Sorry!
Puzzle of the day
Key point: make sure anyone who needs to know is told,
especially those in charge of security across the network and
Simple Security Property: no reads up
Star Property: no writes down
Discretionary Security Property: if mandatory controls say it's okay,
check discretionary controls.
Then add categories:
simple security property is S cannot read O
if L(S) < L(O) or
C(O) not subset of C(S);
star property is S cannot write O
if L(O) < L(S) or
C(S) not subset of C(O)
Basic Security Theorem: A system is secure if its initial state is
secure and no action violates the above rules.
ORCON (Originator Controlled; Graubert)
Document/information can be passed on with approval of originator; real
world justification is that originator of document trusts recipients
not to release documents which they should not.
Untrusted subject x marks object O ORCON on behalf
of organization X
and indicates it is releasable to subjects acting on behalf of
not releasable to subjects acting on behalf of other organizations
without X's permission
any copies made have the same restriction
DAC: can't do this as the restriction would not copy over (y
into C, puts its own ACL on C)
MAC: separate category with O, x, y.
y wants to read O, copy to C;
MAC means C has same category as
O, x, y, so can't give z access to C.
Say a new organization w wants to provide data in B
to y but not to be shared with x or z.
Can't use O's category. Hence you get explosion of categories.
Real world parallel: individuals are "briefed" into a
category and those represent a formal "need to know" policy
that is standard across the entity; ORCON has no central clearinghouse
to categorize data; originator makes rules.
owner of object can't change ACL's relationship with object
on copy, ACL is copied as well (MAC characteristic)
access control restrictions can be tailored on a per-subject/object basis
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Department of Computer Science
University of California at Davis
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Page last modified on 2/8/97