CIS 2005 System Security

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CIS 2005System Security Control

• Module 5
• Operating System Security and Access Control

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Module Objectives

• identify the four types of separation that
  operating systems can use
• describe how memory and address protection can be
  achieved by operating systems
• demonstrate an understanding of different methods
  of access control to general objects

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Module Objectives (Contd)

• understand the need for user authentication
• list various methods of user authentication and
• list advantages and disadvantages of password
  systems.

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Operating System Security Issues

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Operating System Security Issues

• Due to
• Multiple programs running at once
• Multiple users using the same system
• Relates to
• Memory, disk drives, programs, data, networks,
  printers and other input/output devices

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Separation Sharing

• The basis of Operating System protection is
  keeping one users objects separate from other
  users.
• It also needs to provide sharing of some objects.

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Four types of Separation

• Physical separation
• Temporal separation
• Logical separation
• Cryptographic separation

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How to handle Sharing?

• These are various methods in increasing order of
  difficulty to implement and increasing
  protection.
• Do not protect
• Isolate
• Share all or share nothing
• Share via access limitation
• Share by capabilities
• Limit use of an object

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Memory and Address Protection

• Fence
• Relocation
• Base/Bounds Registers
• Tagged Architecture
• Segmentation
• Paging
• Combined Paging with Segmentation
• (Note You need to understand these concepts, but
  not every detail from the textbook.)

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Control of Access to General Objects

• Memory protection can be easily defined because
  access to memory should be done via programs and
  go through certain points of the hardware.
• However, other objects such as files, hardware
  devices and data structures, may be accessed by a
  user, program or other objects. The number of
  points of access may be large and type of access
  more than just read, write and execute.

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Access Control Techniques

• Directory like notes for each user which lists
  the files they can access.
• Access Control List one per object rather than
  user, and lists all subjects with access. To
  reduce overheads, groups and wild cards can be
  used.
• Access Control Matrix like a grid with objects
  on one side and subjects on the other. If access
  rights exist, they are stored at the junction of
  the two.

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Access Control Techniques (Contd)

• Capability subject must produce a ticket to
  confirm access to an object.
• Procedure Oriented Access Control all access to
  an object has to go through a procedure
  protecting it.

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File Protection

• We will look more closely at File Protection
  mechanisms that can be used. A basic
  understanding of the concepts is required.
• All-None protection
• Early use, only some system files were protected
  with a password.
• Group protection

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Single Permissions

• Password or Other Token
• Allow user to apply a password to a file.
• Difficulties are loss, use, disclosure
  revocation.
• Temporary Acquired Permission
• suid (set userid) in Unix operating system
• While running a program, you may have access like
  the owner of the program, not your own.

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Per Object and Per User Protection

• Such as with Access Control Lists and Access
  Control Matrices.
• Difficulties arise when many different variations
  in access are required and therefore, use of
  groups is limited.

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User Authentication

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What is Authentication?

• Authentication refers to the process of verifying
  the claimed identity of a user.
• Most of the protection offered by an Operating
  System is based on the user. If we cannot confirm
  the identity of the user then how can we ensure
  protection.

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Types of authentication

• PIN
• password
• your mothers maiden name

Something you know

• Biometrics
• Fingerprint
• Voice
• Retina

Something you have
Something you are

• Smart card
• Keys
• Dr/Cr card
• Drivers license

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Something you know
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Passwords

• Passwords have been known to be poor
  authentication mechanisms.
• However, due to the legacy of systems which use
  them, it is important to understand the
  procedures that can be followed to improve their
  effectiveness.
• It is also important to understand that they are
  very effective when used in combination with
  other methods.

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Password selection criteria

• Use non-alphabetic characters, upper lowercase
• Choose long passwords
• Avoid actual names or words
• Dont use information easily obtained about you
  (eg, phone number, address, DOB, login name)
• Choose an unlikely password (eg, 2Brn2B)
• Dont write it down
• Change it regularly
• Dont use the same password for different areas

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Password administration issues

• Training and education of users is needed in an
  ongoing basis on the selection of passwords and
  their need for confidentiality of passwords at
  all times.
• As an administrator, do not be too hard on users
  that ask to change their password due to memory
  loss or suspicion of disclosure to third party.
• Use of random checks can help identify weak
  passwords on your system.

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Word of warning

• Remember the Principle of Effectiveness.
• If you make the constraints on passwords such as
  length, time between change or content too
  difficult, some users may resort to writing the
  password down.

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Challenge-response systems

• Password changes every time it is used
• You and the system know a mathematical function
• The system provides an argument and you compute
  and return the value

Argument to the function
User calculates the answer
Answer
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Something you are
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Biometrics

• Biometrics are some immutable, verifiable human
  characteristics, which may be physiological,
  behavioral, or morphological.
• When using biometrics as an authentication
  device, you must accept a certain level of false
  positives and false negatives.

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Examples of biometric data

• Retina patterns
• Finger prints
• Hand prints
• Voice patterns

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Something you have
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Smart cards

• Plastic card with an imbedded silicon chip
• Similar shape to ATM cards, but can be in other
  shapes (eg, a ring, watch, bracelet)
• Produced by Visa, MarterCard, Mondex, American
  Express, Telstra etc.
• Contact-based vs. contactless

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Smart cards processing capabilities

• Magnetic stripe card (not a smart card)
• holds up to 140 bytes of data
• Memory storage only
• holds up to 1Kb of data
• Micro-processor
• holds up to 8Kb of data, 8 to 32-bit CPU
• Optical memory cards
• Uses a piece of compact disk (CD)
• holds up to 4.9Mb

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User Authentication

• Pulling it all together

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Pulling it all together

• Ideally, you dont rely on just one form of User
  Authentication. A combination of two or more
  methods which cover at least two of the
  categories will greatly reduce the chance of
  impersonation.
• Many authentication mechanisms need strong
  procedures/training in place for the users to
  strengthen security.