Notes for November 29, 1999
- Greetings and Felicitations!
- Puzzle of the Day
- 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 organization Y.
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 reads O
into C, puts its own ACL on C)
- MAC: separate category withO, 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
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 (MAC
on copy, ACL is copied as well (MAC characteristic)
access control restrictions can be tailored on a subject/object basis
- Malicious logic
- Quickly review Trojan horses, viruses, bacteria; include animal and
Thompson's compiler trick
- Logic Bombs, Worms (Schoch and Hupp)
- Ideal: program to detect malicious logic
- Can be shown: not possible to be precise in most general case
- Can detect all such programs if willing to accept false positives
- Can constrain case enough to locate specific malicious logic
- Can use: writing, structural detection (patterns in code), common code
analyzers, coding style analyzers, instruction analysis (duplicating
OS), dynamic analysis (run it in controlled environment and watch)
- Best approach: data, instruction typing
- On creation, it's type "data"
- Trusted certifier must move it to type "executable"
- Duff's idea: executable bit is "certified as executable" and
must be set by trusted user
- Practise: Trust
- Untrusted software: what is it, example (USENET)
- Check source, programs (what to look for); C examples
- Limit who has access to what; least privilege
- Your environment (how do you know what you're executing); UNIX
- Practise: detecting writing
- Integrity check files a la binaudit, tripwire; go through signature
- LOCUS approach: encipher program, decipher as you execute.
- Co-processors: checksum each sequence of instructions, compute checksum
as you go; on difference, complain
Send email to
Department of Computer Science
University of California at Davis
Davis, CA 95616-8562
Page last modified on 12/3/99