Notes for February 23, 1998
[ ended here ]
- Greetings and felicitations!
- Reading: Pfleeger, pp. 273-276; Garfinkel & Spafford, pp.
- Practise: detecting writing
- Integrity check files à 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
- Biba: mathematical dual of BLP
- P may read O if L(P) <= L(O) and C(P) SUBSET OF C(O)
- P may write O if L(O) <= L(P) and C(O) SUBSET OF C(P)
- Combined with BLP: continue example
- Theme: military model does not provide enough controls for commercial fraud,
etc. because it does not cover the right aspects of integrity
- Data items: "Condtrained 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
- 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
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
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
associated with a TP. An agent that can certify an entity may not have any
execute rights with respect to that entity.
- Chinese Wall
- Theme: market analyst must uphold confidentiality requirements (no use of
insider knowledge) but can advise different corporations.
- Data items: "objects" (axiomatic), "company datasets" (CD; sets of objects
belonging to a company), "conflict of interest classes" (COI; sets of company
datasets for companies in competition)
- Simple Security Property: Access is only granted if the object requested
(a) is in the same CD as an object already accessed by the subject, or (b)
belongs to an entirely different COI.
- Can derive: if subject accesses object, only other objects in that same CD
can be accessed within the same COI. Also, subject has access to at most one CD
in each COI.
- Sanitization: if it's sanitized then the model does not impose any
- *-Property: Write access is only granted if (a) access is permitted by the
simple security rule, and (b) no object can be read which is in a different CD
to the one for which write access is requested and contains unsanitized
- Can derive: the flow of unsanitized information is confined to its own CD,
but sanitized information may flow freely throughout system
- BLP: not satisfactory. Say user A accesses company dataset B. But then A is
sick, so management has user C do the access. Not possible unless we know for
certain C has not accessed anything else in B's COI; BLP doesn't save this
info. Also, BLP fixes what datasets a subject can access; the Wall allows
- Clark-Wilson: can model it exactly.
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