CS 361 MidtermSample QuestionsInstructor : Dr. Bill YoungName:Read all questions carefully. Answer all questions in the space provided. You may usescratch paper to do your work but only answers recorded on the test paper will be graded.Be as concise as possible. Note: the questions on this sample are all questions asked onpast midterms, but this sample is longer than an hour test.CS361 Midterm: Sample 11. (10 points) Suppose you have a secure system with three subjects and t hree objects,with levels as listed below.TypeName LevelObject Obj1 (H, {A, B})ObjectObj2 (L, {B})ObjectObj3 (L, {A, B})Subject Subj1 (L, {A, B})SubjectSubj2 (H, ∅)SubjectSubj3 (L, {A, B, C})Here H dominates L. You wish to implement a Bell and LaPadula model of securityfor this system. Fill in the access rights (R and/or W) permitted by the model foreach subject/object pair in the a ccess matrix below:Obj1 Obj2 Obj3Subj1Subj2Subj32. (10 points) Assume you have a six sided die that is lopsided in such a way that itrolls each of 1, 2, or 3 twice as often as each of 4, 5, or 6. You wish to send theresults of a series of rolls over a transmission channel. Compute the entropy of thislanguage. (Please write down the appropriate sum; you don’t have to compute anumeric answer.) You might al so be as ked to show an encoding that is be tter thanthe naive encoding and prove that it is better.CS361 Midterm: Sample 23. (10 points) Imagine a Bell and LaPadula-like secure system with the following fiveoperations.(READ s o): if the subj ect and object exist and L(s) ≥ L(o), the subject obtainsthe current value of the object; ot herwise, do nothing.(WRITE s o v): if the subject and object exist and L(s) ≤ L(o), the object getsvalue v; otherwise, do nothing.(CREATE s o): add a new object with the given name, a level equal to the sub-ject’s level, a nd an initial value of 0. If an obj ect of that name exists, donothing.(DESTROY s o): eliminate the designated object f r om the state, assuming thatthe object exists and the subject has WRITE access to it. Otherwise, donothing.(RUN s): the named subject runs some arbitrary private code that cannot accessor modify any of the objects on the system.Describ e a covert channel in this system. That is, show a series of instructions thatwill send a 0 from high to low, and anot her that will send a 1 from high to low.You might also be asked to d i splay the row in the shared resource matrix appropriatefor this system that reflects the channel.CS361 Midterm: Sample 34. (Short answer – 20 points) Fill in the word or phrase that best matches the de-scription provided. In most cases, what is needed is a general term, not a specificinstance of the concept.(a)Security concern involving whether resources ar eon hand when needed.(b)Describ es an information transmission mediumover which a message is transmitted without distortion or loss of informatio n.(c)An encryption algorithm that replaces each sym-bol uniformly by another symbol.(d)The common name for the partial order amongsecurity levels in a hierarchical a ccess control system such as Bell and LaPadula.(e)An information transmission medium that uti-lizes system resouces that were not designed to transmit information.(f)The aspect of security concerning who can alteror modify stored information.(g)Security policy that says that an agent cannotaccess information for a client if he has previously served a client in the same“conflict” class.(h)The property that says t hat the levels of sub-jects and/or objects can vary, but only in ways that don’t violate the systemsecurity properties.(i)Unit used to measure the entropy of a la ngua ge.(j) Describ es any cryptographic system that usesthe same key for encryption and decryption.CS361 Midterm: Sample 45. (10 points) Declassification (lowering the security level of an object) effectivelyviolates the *-property of Bell and LaPadula because the information in that objectflows from high to low.(a) Would raising the level violate either of the BLP properties? Why or why not?(b) Would raising the integrity level of an object violate any principles of Biba’sStrict Integrity model? Explain your answer.CS361 Midterm: Sample 56. (5 points) Suppose you work for a company with a Chinese Wall security policywith clients in the following conflict classes:• { Cadbury, Nestle }• { Ford, Chrysler, GM }• { Citicorp, Credit Lyonnais, Deutsche Bank }• { Microsoft }You have previously worked o n cases for Nestle and Citicorp, and you are ready fora new assignment.List any of your company’s clients for whom you are not able to work as yournext assignment. Assume you can work for a client for whom yo u have previouslyworked.7. (5 points) Assume you have a distributed system with n hosts and you wish toimplement secure pairwise encrypted communication, i.e., from any host to anyother. How many keys are needed if you have symmetric (secret-key) encryption?How many if you have asymmetric (public-key) encryption? This question is aboutmaterial from Week 8 (so not covered on the test).CS361 Midterm: Sample 68. (10 points) Steve Lipner uses the a ccess control rules of Bell and La Padula andof Biba’s Strict Integrity policy to model a commercial security environment. Thefollowing is a simplified version of Lipner’s model.Confidentiality labels are generated in terms of the hierarchical levels (f rom highto low): AM and SL. In addition there are five need-to-know categories: D , PC,PD, SD, T.Integrity labels are defined in terms of the hierarchical levels (from high to low):ISP, IO, ISL. There are two integrity need-to-know categories: ID, IP.Finally, users/objects are given labels according to their role/type:User Role Confidentiality IntegrityOrdinary users (SL, {P C, P D}) (ISL, {IP })System programmers (SL, {SD, T }) (ISL, {ID})System controllers (SL, {D, P C, P D, SD, T }) (ISL, {IP, ID})Object type Confidentiality IntegrityProduction code (SL, {P C}) (IO, {IP })Software tools (SL, {T }) (IO, {ID})System programs (SL, ∅) (ISP, {IP, ID})Assuming the following users/objects have the associated roles/types, fill in thetable below with the R and/or W permissions that the system would allow.NameRole or TypeUser1 Ordinary userUser2System programmerUser3System controllerObj1 Production codeObj2Software toolObj3System programObj1 Obj2 Obj3User1User2User3CS361 Midterm: Sample 79. (5 points) L abels in the Bell and Lapadula model are of the form (L, C), where Lis from a totally ordered set and
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