Notes for February 20, 1998

1. Greetings and felicitations!
   1. Reading: Pfleeger, pp. 273-276; Garfinkel & Spafford, pp. 271-288, 340-356
2. Puzzle
3. Practise: blocking writing to communicate information or do damage
   1. Limit writing (use of MAC if available; show how to arrange system executables)
   2. Isolation
   3. Quarantine
4. Practise: 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
5. Biba: mathematical dual of BLP
   1. P may read O if L(P) <= L(O) and C(P) SUBSET C(O)
   2. P may write O if L(O) <= L(P) and C(O) SUBSET C(P)
   3. Combined with BLP: continue example
6. Clark-Wilson
   1. Theme: military model does not provide enough controls for commercial fraud, etc. because it does not cover the right aspects of integrity
   2. Data items: "Constrained Data Items" (CDI) to which the model applies, "Unconstrained Data Items (UDIs) to which no integrity checks are applied, "Integrity Verification Procedures" (IVP) that verify conformance to the integrity spec when IVP is run, "Transaction Procedures" (TP) takes system from one well-formed state to another
   3. Certification and enforcement rules:
      C1. All IVPs must ensure that all CDIs are in a valid state when the IVP is run
      C2. All TPs must be certified to be valid, and each TP is assocated with a set of CDIs it is authorized to manipulate
      E1. The system must maintain these lists and must ensure only those TPs manipulate those CDIs
      E2. The system must maintain a list of User IDs, TP, and CDIs that that TP can manipulate on behalf of that user, and must ensure only those executions are performed.
      C3. The list of relations in E2 must be certified to meet the separation of duty requirement.
      E3. The sysem must authenticate the identity of each user attempting to execute a TP.
      C4. All TPs must be certified to write to an append-only CDI (the log) all information necessary to resonstruct the operation.
      C5. Any TP taking a UDI as an input must be certified to perform only valid transformations, else no transformations, for any possible value of the UDI. The transformation should take the input from a UDI to a CDI, or the UDI is rejected (typically, for edits as the keyboard is a UDI).
      E4. Only the agent permitted to certify entities may change the list of such entities associated with a TP. An agent that can certify an entity may not have any execute rights with respect to that entity.