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FFW,e HUV ;.HUV 3Ge HUV ;05+HUV 22l H$ ;1H$ 5Ge H$ ;33H$ 44l HHˆ;4HHˆj  !!7 ` Homework 1 G `Due Date : April 20, 2000 :`Points : 100 H` ! s( 10 points ; handout, exercise 1.15) The president of a large software development company has become conpcerned about competitors learning proprietary information. He has determined to stop them. Part of his security nmechanism is to require all employees to report any contact with employees of the companys competitors, even @Zif it is purely social. Do you believe this will have the desired effect? Why or why not? `>( 20 points ; handout, exercise 2.4) Consider a computer system with the set of rights {  r ,  w ,  x ,  a ,  l ,  m ,  o  }. 1 Using the syntax in class (and in section 2.3 of the handouts), write a command  delete_all_right s( p ,  q ,  s ). @hThis command has  p  delete all rights the subject  q  has over an object  s . `pModify your command so that the deletion can occur only if  p  has  m  rights over  s . !0 #Modify your command so that the deletion can occur only if  p  has  m  rights over  s  and  q  does  not  have  o  @rights over  s . 1Ҫ |( 30 points ; handout, exercise 2.6) This question asks you to consider the consequences of not applying the princiު@*ple of attenuation to a computer system,. !2 oWhat are the consequences of not applying it at all? In particular, what is the maximal set of rights subjects @Qwithin the system can acquire (possibly with the cooperation of other subjects)? !3 Suppose attenuation of privilege only applied to  access  rights such as  read  and  write , but not to rights such @as  own  or  grant_rights . Would this ameliorate the situation discussed in the previous part? Why or why not? F rConsider a restricted form of attenuation, which works as follows. Associated with each subject  p  is an *ancestor right a p . A subject  q  is attenuated by the maximal set of rights that it, or any subject to which  q  has UU4,ancestor rights. So, for example, if any ancestor of  q  has  r  premission over a file  f ,  q  can also  r   f . How does @@Uthis affect the spread of rights throughout the access control matrix of the system? 4R`M( 40 points ; handout, exercise 3.1) Prove or give a counterexample: 5*^ hThe predicate  can  share ( a ,  x ,  y ,  G 0 ) is true  if and only if there is an edge from  x  to  y  in  G 0  labelled  a , or if the UUlU7@following hold simultaneously: 64zޤ hVthere is a vertex  with an  s -to- y  edge labelled  a ; 7?`|there is a subject vertex  x  such that  x  =  x  or  x  initially spans to  x ; 8?`there is a subject vertex  s  such that  s  =  s  or  s  terminally spans to  s ; and 9* Uthere is a sequence of subjects  s  =  x 1 , ,  x n  =  x  with  x i  and  x i +1  (1  i  <  n ) being connected by an edge XUU7@Alabelled  t , an edge labelled  g , or a bridge. HHˆ;6HHˆ66 la4q>x!a4qa4qje4'@in[char[(*W"Bold"W*)s],indexes[0,1,char[G],num[0.00000000,"0"]]]}? ?":? 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