Lecture4 - IS2150/TEL2810 IntroductiontoSecurity JamesJoshi

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1 IS 2150 / TEL 2810 Introduction to Security James Joshi Associate Professor, SIS Lecture 4 September 22, 2009 Access Control Model Foundational Results
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Objective Understand the basic results of the  HRU model Saftey issue Turing machine Undecidability 2
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3 Protection System State of a system Current values of  memory locations, registers, secondary storage, etc. other system components Protection state (P) A subset of the above values that deals with protection  (determines if system state is secure) A protection system  Captures the conditions for s tate transition   Consists of two parts: A set of generic rights A set of commands
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4 Protection System Subject ( S : set of all subjects) e.g. users, processes, agents, etc. Object ( O : set of all objects) e.g. processes, files, devices Right ( R : set of all rights) An action/operation that a subject is  allowed/disallowed on objects Access Matrix  A a [ s o R Set of Protection States: ( S O A ) Initial state  X 0  = ( S 0 O 0 A 0 )
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5 State Transitions X i X i +1 τ X τ X   : upon transition  τ i +1 , the  X ├* Y   : the system moves from  state  X to   Y  after a set of transitions X Y * X i X i +1 c ( p , p , …, p ) X c ( p , p , …, p ) X   : state 
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6 Primitive commands (HRU) Create subject s Creates new row, column in ACM;  s does not exist prior to this Create object o Creates new column in ACM o  does not exist prior to this Enter r into  a [ s , o ] Adds  r  right for subject  s  over object   o Ineffective if  r is already there Delete r from a [ s , o ] Removes  r right from subject  s  over object   o Destroy subject s Deletes row, column from ACM; Destroy object o Deletes column from ACM
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7 Primitive commands (HRU) Create subject s Creates new row, column in ACM;  s does not exist prior to this Precondition:  Precondition:  s s         S S Postconditions: Postconditions: S ´ =  S   s  },  O ´ =  O   s  } ( 2200 y     O ´)[ a ´[ s y ] =  ] (row entries for s) ( 2200 x     S ´)[ a ´[ x s ] =  ] (column entries for s) ( 2200 x     S )( 2200 y     O )[ a ´[ x y ] =  a [ x y ]]
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8 Primitive commands (HRU) Enter r into  a [ s , o ] Adds  r  right for subject  s  over object   o Ineffective if  r is already there Precondition:  Precondition:  s s         S S o o         O O Postconditions: Postconditions: S ´ =  S O ´ =  O a ´[ s o ] =  a [ s o  {  r  } ( 2200 x     S ´)( 2200 y     O ´)  [( x y ) ( s o   a ´[ x y ] =  a [ x y ]]
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This note was uploaded on 11/02/2009 for the course SIS 2150 taught by Professor Joshi during the Spring '09 term at Philadelphia.

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Lecture4 - IS2150/TEL2810 IntroductiontoSecurity JamesJoshi

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