Notes for November 21, 2000
- Greetings and Felicitations!
- a. Turn back midterm
- b. Go over project
- Puzzle of the day
- Principal and identity
- Users, groups, roles
- Identity on the web
- Host identity: static and dynamic identifiers
- State and cookies
- Anonymous remailers: type 1 and type 2 (mixmaster)
- Privilege in Languages
- Nesting program units
- Temporary upgrading of privileges
- Access Control Lists
- UNIX method
- ACLs: describe, revocation issue
- MULTICS ring mechanism
- MULTICS rings: used for both data and procedures; rights are REWA
- (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
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
rings 40-63: cannot access a
- 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
- 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
- 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
- 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 Dis can access the file
AND-Access: need all n deciphering functions to get K:
R = E1(E2(...En(K)...))
Puzzle of the Day
Your UNIX system has been attacked. The uucp entry in your /etc/passwd
file has a UID of 0. You have run ps to see if any unusual processes
were executing. None were. You ran ls to find any unusual files or
directories. None were reported. You ran du to determine if the size of
any file system was unusually large (indicating hidden files). Nope.
You suspect that someone has, somehow, hidden files (or directories) and
an executing process. You decide to start at the /dev directory, to see
if they created any new device files. Again, an ls lists only those
files you expect to see. But you are still suspicious, and want to
confirm the results.
What would you do?
You still suspect that the attacker left an illicit process executing.
But ps showed nothing. How would you confirm or refute your suspicion?
Office: 3059 Engineering Unit II
Phone: +1 (530) 752-8060
Fax: +1 (530) 752-4767
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.
Page last modified on 11/22/2000