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FEW)a Macro Name }?H =rD.0?H FEW*a Replace With }H =tD/1H FEW+a Comments }? =vD0B? FFW,a HUV ;.HUV ❝3G܁e HUV ;05+HUV 22靕l H$ ;1H$ 5G܁e H$ ;33H$ 44靕l HH;4HHŁi117 ` Homework 3 G ܁`3Due Date : March 2, 1999 Points : 200 H` ! z( 20 points ) A computer security expert claims that one of the measures necessary to obtain computer security is @Pthe separation of programmers and operators Is she right? Justify your answer. ;`6( 20 points ) Consider the UNIX file system. !7 oHow could a mandatory access policy be defined so that a user has access to a file only if the user has access @Ito all subdirectories higher (closer to the root) in the file structure? 8`)What would be the effect of this policy? !A {( 20 points ) Why is labelling (associating labels with objects and subjects) a security requirement? That is, why rcould a trusted computing base not simply maintain an access control table with entries for each subject and each @>object rather than having labels associated with each object? !6 t( 30 points )Compare the Clark-Wilson model rules to typical software engineering approaches for protecting @+abstract data types from program routines.  ( 40 points ) Suppose information is classified on the basis of (i) content level ( C  for confidential and  S  for secret), *@wand (ii) department ( D 1 , ...,  D 4 ), where the relationship among departments is given by: `DD 1      D 3      D 4 0`&D 2      D 4 1`4D 1      D 2  =   2`>D 2      D 3       3 vIn case of proper containment,  D i      D j , two distinct departments are assumed,  D i  and  Dj  D i . If  D i      Dj        and UUuthere is no containment of one in the other, it is useful to define an additional department in the intersection. By 1the Bell-LaPadula Model, the natural permissible information flows are dictated by the partial orders (i)  C      S  *@oand (ii)  D i      Dj  if and only if  D i      Dj . 4UUK`#Assume the set of security classes 5W`K  = { ( x ,  y ) |  x     { C ,  S } and  y  = some department } 9`9Construct a lattice of secure information flow such that D`1K  contains a minimum number of classes; and E*`N( x 1 ,  y 1 )    ( x 2 ,  y 2 ) if and only if  x 1      x 2  and  y 1      y 2 . UUU& ( 70 points ) We are now going to test  lassen  from the point of view of the ordinary user. The goal is to perform 0U%nany of the following: read the file /README, alter the file /CHANGEME, or lock up the system (a denial of serwvice attack). As in the first homework, the first step in a penetration test is to hypothesize flaws, or potential vulqnerabilities. For this exercise, you must assume you are analyzing the system as though you have no access to it @Qother than from the network. You will hypothesize potential flaws and test them. !> nPlease devise three possible system-based vulnerabilities on the system. You are also to describe how to test lfor the flaw, possibly with the aid of an atack tool (but without one is fine, and indeed preferable). Your @9description should have the format given on the web page <`Jhttp://seclab.cs.ucdavis.edu/projects/vulnerabilities/doves/template.html =`&Run your test and report the results. ? }Please post your description, and the results of your attack, to the newsgroup  ucd.class.ecs253.d . Do not post nany attack tools you use  but do submit them with your answer to this question. Your submitted answer may vbe a copy of your news posting, plus any attack tools used. As part of the requirement for this answer,  each stu ~dent must submit 3 different potential vulnerabilities ; the first poster of each vulnerability gets credit for it. So be @?sure your vulnerabilities are different than your classmates! !@ zEach registered student in the class has been given an account on  lassen . Your account name is the same as your ~name on  toadflax  or, if you do not have one there, on the CSIF. Your password is the first 8 digits of your student @nidentification number as given by the registrar.  Please change your password as soon as you log in . Bnj` Extra Credit WC܁~U nWhat assumptions with respect to trust would an implementation of the Clark-Wilson model make? In particular, HH;6HH 66 靕l d;;<@H$ ;<;>H$ == 靕l H$ ;=;H$ <W܁܁hEFebruary 17, 1999ECS 253 / CC 746 DA WINTER 1999Page 1  HUV ;>;<@HUV ?? 靕l HUV ;?;HUV ❝>W܁܁lDLast modified at  5:43 pm on Wednesday, February 17, 1999  HH;@;>HHAA 靕l HH;A;HH❝@W܁܁` }?H =xD1C?H FFW-a }H =zDBH FFW.a d=~EEd=DdFF 靕l d=DdRCERUX[^adgjmpsvy| %).1dLeftd;Rightd ReferenceddHTMLdDHTMLd HeadingsdĿ@@ QMapping Table Title. Ŀ@@ QBody.  f@PQTitleBody. 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