ETRI CIS OHP Form

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Authorization
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Authorization ?

• .restrict the potential actions of users.
• The aim is that the computing environment
  guarantees that only legitimate users can obtain
  access to computing facilities, and that only
  allowable and legitimate actions will be
  performed
• von Solms Eloff
• Synonyms Access Control, Entitlement

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Introduction

• Authorization Basics
• Authorization Models
• DAC
• MAC
• RBAC
• Authorization in Workflow Systems
• Authorization in UNIX systems
• Secret Sharing

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Motivation
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Limitations of Authorization

• Authorization relies on Authentication
• Effectiveness bounded by the system as a whole
  (e.g. buffer overflow)
• misbehavior of users, social component
• insider threat

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Authorization Models
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Access Control Mechanisms

• Supporting a DAC policy
• directory list
• access control list
• access control matrix
• Supporting a MAC policy
• Military security model
• BellLaPadula model

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Discretionary Access Control
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Directory List
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Access Control List
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Access Control List Example
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Access control matrix
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Mandatory Access Control Models

• Military Security Model
• principle of least privilege
• security classification hierarchy (clearance for
  subjects)
• each piece of information classified
• enforce information compartmentalization

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The security levels of the Military
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Military Security Model (I)

• A subject can obtain access to an object if and
  only if the following two conditions are true
• security_class(subject) gt security_class(object)
  
• compartment (object) Í compartment (subject)

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Military Security Model (II)
Two Compartments Nuclear Missiles (NUC) and
Satelliten Verteidigungssystem (SDI) Three
Security Levels Top secret (top), confidential
(con) and unclassified (un)
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Mandatory Access Models

• Bell LaPadula Model
• widely referenced model
• successor of military model
• subject and object labeling
• customized classification hierarchy
• allowable flow of information

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Mandatory Access ControlBell LaPadula Model

• simple security property No-read-up
• a subject Si can have read access to an object
  Oj only if
• C(Si) gt C(Oj)
• star-property No-write-down
• a subject Si can have write access to an object
  Oj only if
• C(Si) lt C(Oj)

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Bell LaPadula Model - Example
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Role Based Access Control (RBAC)
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UNIX Security File Permissions (I)

• Subjects Objects

• user e.g. root, daemon,
• guest, nobody, knorr, ...
• group e.g. admins, ikm,
• students, ...
• other

• files
• directories
• links (symbolic, hard)
• ...
• Access Rights
• Permissions, Privileges
• r, read
• w, write
• x, execute

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UNIX Security File Permissions (II)

• Read
• To be able to view contents of a file
• To be able to read a directory (listing)
• Write
• To be able to add to, rename or change a file
• To be able to delete, rename or move files in a
  directory
• Execute
• To be able to run a binary program or shell
  script
• To be able to enter a directory
• Privileges have no meanings for symbolic links.

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UNIX Security File Permissions (III)
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UNIX Security File Permissions (IV)
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UNIX Security chmod(1) Command

• File permissions are changed with the chmod(1)
  change mode command by the owner
• of a file. There are two syntaxes you can use
• (1) chmod DDD file file ...
• The DDD are three octal digits representing bits
  of protection
• rwx rwx rwx can be thought of as 111 111 111
  in binary
• 111 111 111 can be thought of as 777 octal
  (14 12 1 7)
• you specify an octal numbers whose bits are in
  the places you want turned on
• (2) chmod ugoa-rwx file ...
• This is the "symbolic" method
• chmod urwx means give the User Read, Write,
  and eXecute
• chmod grx means give the Group Read and
  eXecute
• chmod o-rwx means take Read, Write, and
  eXecute away from the Others
• chmod ax means give All eXecute permission
• chmod gr means give Group Read and make sure
  it has nothing else
• Symbolic modes can be strung together with
  commas
• chmod urwx,g-w,o-rwx for instance

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UNIX Security umask(1) Command

• umask user file-creation mode mask
• This is BACKWARDS to the chmod command
• It tells you which permissions will NOT be given
  and is used as a TEMPLATE
• 077 or 77 means don't let anyone but the User do
  anything with my files
• 027 or 27 means let the User do anything, let the
  Group do anything but Write, don't let the Others
  do anything

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UNIX Security other commands

• chown change owner
• Nowadays, only executable by owner of file
• chgrp change group
• Groups password needed
• whoami gives users identity
• only admin can add new users and groups
• Groups of user are listed in the file /etc/group