Notes for February 21, 1997

1. Hello
2. Puzzle of the day
   1. Bob's mail box is a symbolic link to the password file
   2. Bob also owns cheryl's mail box
3. Practise: blocking writing to communicate information or do damage
   1. Limit writing (use of MAC if available; show how to arrange system executables); review quickly
   2. Isolation
   3. Quarantine
4. Trust
   1. Untrusted software: what is it, example (USENET)
   2. Check source, programs (what to look for); C examples
   3. Limit who has access to what
   4. Your environment (how do you know what you're executing); UNIX examples
   5. Least privilege; above with root
5. Practise: detecting writing
   1. Integrity check files à la binaudit, tripwire; go through signature block
   2. LOCUS approach: encipher program, decipher as you execute.
   3. Co-processors: checksum each sequence of instructions, compute checksum as you go; on difference, complain
6. Lattice Model
   1. Set of classes SC is a partially ordered set under relation ¾ with GLB (greatest lower bound), LUB (least upper bound) operators
   2. Note: is reflexive, transitive, antisymmetric