network,security

1. 111
Trusted Systems and Trojan Horse
Done by : Hany Nasser
Supervised by : PhD Nabil Hamdy

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Trusted Systems
 Systems used to enhance the ability to
defend against intruders and malicious
programs.
 based on levels of security .

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Multilevel Security
 When multiple categories or levels of data are
defined, the requirement is referred to as
multilevel security.
 Typically use Mandatory Access Control.
 Primary Security Goal: Confidentiality (ensures
that information do not flow to those not cleared
for that level).

4. 4
Security Goal of MLS
 There are security classifications or security
levels
 Subjects have security clearances
 Objects have security classifications
 Example of security levels
 Top Secret
 Secret
 Confidential
 Unclassified
 In this case Top Secret > Secret > Confidential
> Unclassified

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Data Access Control
 Through the user access control
procedure (log on), a user can be
identified to the system.
 Associated with each user, there can be
a profile that specifies permissible
operations and file accesses.
 The operating system can enforce rules
based on the user profile.

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Data Access Control
 General models of access control:
 Access matrix
 Access control list
 Capability list

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Data Access Control
 Access Matrix: Basic elements of the model
 Subject
 Object
 Access right

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Data Access Control
 Access Matrix

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Data Access Control
 Access Control List: Decomposition of
the matrix by columns

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Data Access Control
 Access Control List
 For each object, An access control list lists
users and their permitted access right.
 The list may contain a default or public
entry.

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Data Access Control
 Capability list: Decomposition of the
matrix by rows

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Data Access Control
 Capability list
 A capability ticket specifies authorized
objects and operations for a user.
 Each user have a number of tickets.
 Capabilities are not forgeable.

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The Concept of
Trusted Systems
 Multilevel security
 Definition of multiple categories or levels of data
 A multilevel secure system must enforce:
 No read up
 No write down

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The Concept of
Reference Monitor

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The Concept of
Reference monitor
 Reference Monitor
 Controlling element in the hardware and
operating system of a computer that
regulates the access of subjects to objects
on basis of security parameters
 The monitor has access to a file (security
kernel database)
 The monitor enforces the security rules (no
read up, no write down)

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The Concept of
Reference Monitor
 Properties of the Reference Monitor
 Complete mediation
 Isolation
 Verifiability

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Trojan Horse
 It is a type of malware (malicious
software) designed to provide
unauthorized, remote access to a user’s
computer.
 Trojan horses do not have the ability to
replicate themselves like viruses.
 With the help of Trojan, an user can get
access to the Trojan horse infected
computer and would be able to access the
data.

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Types of Trojans
 Command Shell Trojan
 Email Trojan
 Document Trojan
 FTP Trojan

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Trojan Horse Defense

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Indications of Trojan Attack
 Browser redirects to unknown pages.
 Anti virus is disabled.
 Strange pop ups or chat messages appear
on the system.
 The computer shuts down automatically.
 Ctl+Alt+Del stops working.
 Printer prints documents automatically.

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Examples of Trojan
 Net bus
 Sub seven
 Y3K remote administration tool
 Back Orifice
 Beast
 Zeus
 The Black hole Exploit kit
 Flashback Trojan

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How to avoid being infected ?
 Do not surf or download anything from
stranger website.
 Do not open the unexpected attachments
on emails.
 We need an antivirus to protect our
computer from being infected.

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References
 Cryptography And Network Security, 4th
Edition by William Stallings.
 Computer Security, 2nd edition by Dieter
Gollman.
 Specifications of multi-level security
research by Daryl McCullough.

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Thank you