ADCS
Chapter 8
PC And Network Security
“Keys to success... Research your
idea, Plan for success, Expect
success, & just plain do it! It amazes
me how many people skip the last
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success will follow you every step of
the way!" -- Josh S. Hinds
Prepared by:
SITI ZAINAH ADNAN
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comment,
please feel free to email me at
sitizai@hotmail.com
Your cooperation is very much
CS262/0602/V2 appreciated ! Chapter 8 - 1
ADCS
Chapter 8
PC And Network Security
TOPICS
• Introduction
• Contributors to Security Problems
• Security Measures
• Protection for File
• Communication Security
• Network Security Issues
– Encryption in Networks
– Network Access Controls
– Network Firewall
• Traffic Control
CS262/0602/V2
Chapter 8 - 2
ADCS
References
• Book (available at the
Informatics library)
– http://www.cert.org/research/JHT
hesis/Word6/
• Notes (available at IVC)
CS262/0602/V2
Chapter 8 - 3
ADCS
Introduction
• Recently the use of personal
computer and computer
communication network has
spread substantially.
• It is very important to define the
security measures at all levels viz.
PC, communication media and
network (both LAN and WAN).
CS262/0602/V2
Chapter 8 - 4
ADCS
Introduction
• PC:
– Small machine
– Used by single person at a time
– With single user system, many copies
of software needed to run the
program on each different machine
• Mainframe:
– More conventional
– Multi-user machine
– One copy of software is bought by
computing centre, and all users can
make use of the one copy of the
executable code of program
CS262/0602/V2
Chapter 8 - 5
ADCS
Contributors to
Security Problems
• The major problem facing personal
computer users involve secrecy,
integrity and availability of
programs, data and machines.
• Hardware Vulnerabilities
– Most PCs do not have any
hardware level protection
– Although PCs have simple
password authentication, such
features can be easily bypassed
by clever users.
– The controls for PCs are much
less stringent than for
mainframe computers
– Limited memory protection
CS262/0602/V2
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ADCS
Contributors to
Security Problems
• Other Vulnerabilities.
– Users are the source of security
problems, but not PCs.
– Users often do not consider the
security risks when dealing with
program or data within PC.
CS262/0602/V2
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ADCS
Contributors to
Security Problems
• Vulnerabilities in PC security:
– Low awareness level - PC is just
another office tool - typewriter
– Few hardware controls - no
restricted access to I/O
– No audit trail - impossible to tell
who has accessed what and
when
– No unique responsibility - no
one will responsible for the
maintenance of the PC, since PC
is stored by different users
– Environment attack - food,
smoke, power surge
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Chapter 8 - 8
ADCS
Contributors to
Security Problems
– Physical access - PC left
unattended, anyone can access
– Care of media, components diskettes are not keep properly
– No backup
– Questionable documentation poor documentation, leads to
mistake, no guideline
– Amateur quality software - they
may not practice full/complete testing
during program development, so
possible vulnerabilities is untested
– High portability - vulnerable to theft,
easily moved from one place to
another
• Note: Amateur - one lacking the skill of a
professional
CS262/0602/V2
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ADCS
Contributors to
Security Problems
– Magnetic retention - ERASE file
doesn’t actually erase/overwrite
the file, others may access it
– Combination of duties - most
PC application designed for user
to perform all task/steps, may
lead to malicious act e.g. can
delete files etc
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ADCS
Security
Measures
• Although the list of vulnerabilities is
long and varied, the issues involved
fall into four major classes:
– User responsibility
– Improper procedures for use
– Hardware concerns
– Software concerns
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ADCS
Security
Measures
• Why PC is more vulnerable than
mainframe:
– No dedicated h/w protection
– Lack of physical security
– No audit protections
– Users less aware of security
– Lack of user training
– PC s/w is less reliable
CS262/0602/V2
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ADCS
Security
Measures
• User Awareness of
Responsibilities
– Computer users must
understand the vulnerabilities of
computers.
– Awareness can be developed
from:
• Reading
• User awareness programmes
• High-level assessment of the
risk of computing
• Unpleasant and costly
experience
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ADCS
Security
Measures
• Procedures for Use
– Vulnerabilities can be controlled by
administrative procedures.
– Sensible policies can reduce the
risk associated.
– Policy could include statements on:
• Unattended machines
• Care of media
• Backups
• The environment
• Separation of duties
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ADCS
Security
Measures
• Procedures to improve PC
security:
– Do not leave PCs unattended if
they contain sensitive information
or are running sensitive
computations
– Do not leave printers unattended
if they are printing sensitive output
especially if it’s located in public
place
– Secure media as carefully as you
would the equivalent confidential
reports - locked up diskette and
PC, turn off PC to clear volatile
memory, label the disk etc
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ADCS
Security
Measures
– Do not allow eating or drinking,
or smoking in any room
containing a PC
– Treat media with care - keep
away from magnetic field
– Perform periodic backups
– Practice separation of authority no one person has authority to
affect sensitive data e.g. 2
accounting system on 2 systems,
by 2 people so that figures must
balance between the 2 systems
CS262/0602/V2
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ADCS
Security
Measures
• Hardware Controls
– Hardware controls are not
effective for PCs as compared to
mainframes.
– PCs have no privileged mode for
hardware executive or memory
protection.
– Some controls that depend on
hardware are:
• Secure the equipment through
bolting/screw the PC on the
desk
• Consider add-on hardware
access control devices such
as smart card
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ADCS
Security
Measures
• Software Controls
– Common software vulnerabilities
include:
• The lack of audit trail.
• The use of software from
entrusted sources - source of
virus
• Poor documentation - no
proper guideline, lead to
mistake
• The lack of operating system
controls, such as reuse of file
space or access control - lead
to sensitive data exposure to
other users
CS262/0602/V2
Chapter 8 - 18
ADCS
Security
Measures
• Notes: audit trails
– A chronological record of
computer activity automatically
maintained to trace all use of
computer
– For security purpose, it’s
preferable that the record be
maintained by the OS
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ADCS
Security
Measures
– Protection against software
vulnerabilities:
• Use all software with full
understanding of its potential
threats e.g. communication s/w
can leak information, program
compute incorrect answer, s/w
can destroy files
• Don’t use software from
dubious sources - s/w from
large, reliable manufacturers
less likely to exhibit problems,
don’t access s/w from bulletin
board
• Note: Dubious - not clear or obvious;
questionable; doubtful
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ADCS
Security
Measures
• Be suspicious of all results many application developed by
nonprogrammers, they don’t
follow SE practices (design,
methods, thorough testing),
therefore data might be
incorrect or may corrupt data
from other sources
• Maintain periodic complete
backups of all system
resources.
CS262/0602/V2
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ADCS
Protection
for File
• Essentially, there are four types of
protection applicable to PC files:
– Access controls - provide by s/w
– User-invoked encryption
– Copy right protection - limits
someone ability to copy a file
– No protection - control the
environment
CS262/0602/V2
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ADCS
Protection
for File
• Access Controls
– Provided either as a part of the
operating system or as auxiliary
packages.
– Most PC operating systems do not
provide access controls to files any user can access any file
– Where these controls are
available, people do not use
them, this negligence results from
environment and ease of use of
PC
CS262/0602/V2
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ADCS
Protection
for File
• User-invoked Encryption
– Any user can perform encryption;
no complicated or expensive
mechanism is required.
– This technique provides
protection against casual
observers and for sensitive
applications.
CS262/0602/V2
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ADCS
Protection
for File
• Copy Right Protection
– There are essentially three ways
to prevent a file from being
copied:
• One can depend solely on
software.
• One can use a combination of
software and hardware
device.
• One can use hardware alone.
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ADCS
Protection
for File
• Software Techniques
– Uses software magnetic media
design to hide certain control
features - s/w can only be run if
the magnetic media is present
when executing program
– A program check sum is created
to prevent modification e.g. use
hash function to verify the s/w
serial number
CS262/0602/V2
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ADCS
Protection
for File
• Software and Hardware
Combinations
– A hard token called key is used
together with the software
package in order for the program
to run - Dongle (h/w attached to
serial port) to prevent
unauthorised duplicate, s/w will
not operate without the key (e.g.
server key)
– Such feature is commonly used for
expensive PC software such as
CAD/CAM software.
CS262/0602/V2
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ADCS
Protection
for File
• Hardware Techniques
– This method uses translating the
program code into a micro chip.
– The micro chip is then plugged into
the PC and run during power-up.
– Such method is commonly used for
time-sensitive applications where
performance is the key concern.
– For example; Simple automated
gate control system.
• No Protection
– Provide no protection at all.
– However, this is freely acceptable
by the public domain users
– e.g. shareware - no control at all
CS262/0602/V2
Chapter 8 - 28
ADCS
Security Modems
• Security for a single user
communicating with a computer via a
modem
• Modem – allows anyone to call the
computer
• Protections:
–
–
–
–
Call-back or dial-back modems
Password modems
Encryption modems
Silent modems
CS262/0602/V2
Chapter 8 - 29
ADCS
Security Modems
• Call-back or dial-back modems
– Attached to computer
– User call the computer and enter
login ID
– Modem then hangs up, figures out
the telephone number of office or
home where the authorised owner
of login ID should be, then calls the
number
– Only then the user can log into the
system
CS262/0602/V2
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ADCS
Security Modems
• Password modems
– User must enter a password before
the modem will connect the user to
the computer
• Encryption modems
– All information encrypted as it’s
sent
– Protection against wiretapping and
from unauthorised users
– Used in pair at both sender and
receiver ends
CS262/0602/V2
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ADCS
Security Modems
• Silent modems
– The modem won’t signal that the
connection has been made until the
login process is begun
– It is intended to keep crackers
doing random dialling from knowing
that they have found a computer
CS262/0602/V2
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Communication
Media
ADCS
• Wire pair and Coaxial cable:
– Passive wiretapping is just
listening - intercepting the
communication without
damaging the cable
– Active wiretapping is injecting
something into the communication
line by cutting the jacket onto a
wire
– Wiretapping can be achieved at
junction boxes or place where
cable is exposed to public.
– Other security concerns include
wire interference that causes
communication malfunction.
CS262/0602/V2
Chapter 8 - 33
ADCS
Communication
Media
• Microwave and Satellite:
– In both cases, the signals are
available in air.
– Any one with appropriate
equipment can retrieve
information from open air
signals.
• Optical Fiber:
– The connectors used is the most
vulnerable point for most fiber optic
connections.
– Light signals can be reflected into
multiple directions if the
connection is not made properly.
– Offers the best security compared
to other media.
CS262/0602/V2
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ADCS
Network Security
Issues
• Users of computer networks have
the same expectations as users of
conventional computer systems:
–
–
–
–
Delivery of accurate messages
Delivery only to intended recipient
Protection from loss
Modification or observation of
messages in transit
– Reliable services
• Several inherent security problems in
networks include:
– Share resources
– Complexity of networking
systems
CS262/0602/V2
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ADCS
Encryption in
Networks
• Encryption is a very powerful tool for
providing privacy, authenticity, integrity
and limited access to data.
• Networks often secure data using
encryption in combination with other
controls.
CS262/0602/V2
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ADCS
• Link Encryption:
– Provides encryption feature
between two computer systems
through a line.
– Data is encrypted just before
system place it on
communication link (layer 1 and
2 – OSI model)
– But message is plaintext inside the
hosts
– If the intermediate hosts are
compromised – all message
passing thru them are exposed
– Commonly used to secure leased
circuit between two companies
provided their hosts are secure
– Provides node authentication.
CS262/0602/V2
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ADCS
– Advantage :• Require only one key per host
pair
• Encryption is invisible to user
– Disadvantage :• Inflexible hardware
implementation
• Data is not secure at sender,
receiver and intermediate node.
CS262/0602/V2
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ADCS
Encrypted message
CS262/0602/V2
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ADCS
• End-to-end Encryption:
– Provides security from one end of
the transmission to another.
– Usually done using software,
therefore it is more flexible
compared to other (layer 6 or 7 of
OSI model)
– Precedes all routing and
transmission processing of the
layer, the message is transmitted in
encrypted form throughout the n/w
– Messages sent through hosts are
protected
– Commonly applied to user
connection to host.
– Provides user authentication.
CS262/0602/V2
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ADCS
– Advantage :• Flexible software implementation
• Message is encrypted in the
intermediate nodes
– Disadvantage :• Require one key per user pair
• Encryption is apply by user
CS262/0602/V2
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ADCS
CS262/0602/V2
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ADCS
Network Access
Controls
• Is concerned about protection of
data within the network.
• Similar to access control for computer
system, but network access controls
have several unique features.
CS262/0602/V2
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ADCS
Network Access
Controls
• Port Control:
– A serious vulnerability to a network
is dial-in port access.
– User authentication is difficult
when user dials in from a
telephone.
– Port protection is accomplished by
several administrative and
hardware techniques.
CS262/0602/V2
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ADCS
Network Access
Controls
• Automatic call-back:
– Provide authentication to ensure
that caller is the correct person for
the connection.
– Call forwarding feature must be
implemented with careful network
configuration controls.
– Provide table of telephone
number for authorised users (must
be well protected against
modification)
– e.g. a user can call at 3 different
location (different tel. No) provided
that the user gives all 3 tel. No to
the computer as legitimate no.
CS262/0602/V2
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ADCS
Network Access
Controls
– e.g. Callback features in
Windows 2000 Server:
• The Remote Access Service
(RAS) server calls the remote
access client after the user
credentials have been verified
• The server calls the caller back
during the connection
establishment at a telephone
number set by the administrator
• Other than for authentication, it
can save the caller telephone
charges as well
CS262/0602/V2
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ADCS
Network Access
Controls
• Differentiated access rights:
– Sensitive data can be protected by
limiting the places from which
access is allowed
– Access to sensitive data objects
must be from direct connection
(secure place e.g. office) and not
thru another n/w host
– Useful for sale representative:
• Can transfer non sensitive data
from outside
• Can only access data (sales
projections, pricing structure) at
office
CS262/0602/V2
Chapter 8 - 47
ADCS
Network Access
Controls
• Node authentication:
– Process of network nodes
convincing other nodes that it is
authentic.
– Protocols involving encryption are
used to verify the identity of nodes
by using secret key and public
key
– E.g. SSL protocol verifies both the
client and server nodes before the
communication takes place
CS262/0602/V2
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ADCS
Network Firewall
• A firewall is a system or group of
systems that enforces an access
control policy between two
networks.
• It filters all traffics between a
protected (inside) n/w and a less
trustworthy (outside) n/w
• The purpose is to keep “bad” things
outside a protected environment
CS262/0602/V2
Chapter 8 - 49
ADCS
Network Without A Firewall
Internet
Private Network
CS262/0602/V2
Chapter 8 - 50
ADCS
CS262/0602/V2
Chapter 8 - 51
ADCS
Network Firewall
• The firewall can be thought of as a
pair of mechanisms.
• One which exists:
– To block traffic - prevent access
from outside
– To permit traffic - allow traffic to
pass from inside to outside ( one
way traffic)
• It implements an access policy.
CS262/0602/V2
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ADCS
Network Firewall
• Purpose of firewall
– To allow the organisation to do
business transaction over
Internet.
– Also to protect the sensitive or
proprietary data.
– To keep hackers out of the
network.
– Act as corporate “ambassador”
to Internet e.g. to do promotion
– Used to store public information
on products and services, files to
download etc.
– As a check point through which
all traffic must pass.
CS262/0602/V2
Chapter 8 - 53
ADCS
Network Firewall
• Services provided by firewall
– Some firewall permit only Email
traffic through them. Thereby
protecting the n/w against any
attacks
– Protect against unauthenticated
logins from the “outside” world, to
prevent vandals from logging into
machines on the n/w
– Provide single check point where
security and audit can be
imposed.
CS262/0602/V2
Chapter 8 - 54
ADCS
Network Firewall
• The four common firewall
implementations are:
– Packet filtering
– Single-Homed Bastion host
– Dual-Homed Bastion host
– Screened subnet with DMZ
CS262/0602/V2
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ADCS
Network Firewall
• The Packet-Filtering Firewall
– It is the simplest among other four
models.
– It is inexpensive.
– It analyzes network header fields
and get the IP addresses and Port
numbers (UDP or TCP) of the
incoming packet.
– It can filter unwanted traffics.
CS262/0602/V2
Chapter 8 - 56
ADCS
Network Firewall
• The Packet-Filtering Firewall
– The drawback are:
• It needs a good technical
expertise.
• It solely depends on single
device
• It doesn’t hide internal
network IP addresses
• Poor monitoring and logging
capabilities
• Once router compromised,
then no security for internal
network
CS262/0602/V2
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ADCS
Packet Filtering
InterNet
Routes or blocks packets,
as determined by site's
security policy.
Screening
Router
Internal
Network
CS262/0602/V2
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ADCS
Network Firewall
Single-Homed Bastion
• One computer acts as the firewall and
the network interface
• Information coming from an external
network first goes to the bastion,
then it will be forwarded to the
company’s network.
• Packet filtering router is configured
to forward all the incoming information
to the bastion host
• Bastion provides application
filtering. It can be configured to
disallow file downloading, if the
company policy prohibits downloading.
CS262/0602/V2
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ADCS
Network Firewall
Single-Homed Bastion
• Can hide internal network
configuration using NAT (Network
Address Translation)
• The disadvantages are
– Increased cost and reduced
performance
– If router’s access list is
compromised the whole network
can be accessed
– The security of internal network
solely depends on the router
CS262/0602/V2
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ADCS
Screened Host Gateway
Single-Homed Bastion
Bastion
Host
Permitted
Blocked
Internet
Protected
network
Router ,w/Packet
Screening
CS262/0602/V2
Chapter 8 - 61
ADCS
Screened Host Gateway
Single-Homed Bastion
InterNet
Firewall
Screening
Router
Bastion Host
Internal
Network
CS262/0602/V2
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ADCS
Network Firewall
Dual-Homed Bastion
• It uses a computer with two or
more NIC (network interface card),
with their IP forwarding features
disabled.
• Software-imposed firewall help
forward valid packets between
subnets e.g. can check for Telnet,
Rlogin, FTP, HTTP/Web or
NNTP/Usenet news
• It is more secure because it creates a
complete physical break between
your network and any external
network, such as Internet.
CS262/0602/V2
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ADCS
Network Firewall
Dual-Homed Bastion
• Advantages:
– Can perform elaborate logging or
support user authentication
– It doesn’t expose internal IP
addresses
– Even router is compromised and
access list changed to allow IP
packets from outside hosts to
internal network, packets are
blocked by proxy since IP
forwarding switched off at kernel
level
• Disadvantages
– If the proxy is compromised, it can
be used to gain access to internal
network
CS262/0602/V2
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ADCS
Dual Homed Gateway
Dual-Homed Bastion
Proxy Services
Bastion
Host
Protected
network
Internet
Router
CS262/0602/V2
Chapter 8 - 65
ADCS
Dual Homed Gateway
Dual-Homed Bastion
Proxy Services
InterNet
External Host
Real Server
Firewall
Proxy Server
Dual homed Host
Internal
Network
Internal Host
Proxy Client
CS262/0602/V2
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ADCS
Network Firewall
Screened-Subnet Firewall with DMZ
• It is also known as Demilitarized
Zone (DMZ)
• It uses bastion host to support the
circuit-level and application level
gateways while defining DMZ.
• The DMZ functions as a small
isolated network between the
Internet and the internal network.
• The DMZ can be used to host
publicly accessible
internetworking servers, including
Web and FTP servers, Mail servers
or front-ends for E-commerce
CS262/0602/V2
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ADCS
Network Firewall
Screened-Subnet Firewall with DMZ
• Advantages:
– Internal network is invisible to
internet and it cannot construct
direct routes to the internet
CS262/0602/V2
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ADCS
De-Militarized Zone
Architecture
CS262/0602/V2
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ADCS
De-Militarized Zone
Architecture
CS262/0602/V2
Chapter 8 - 70
ADCS
De-Militarized Zone
Architecture
Firewall
InterNet
Exterior Router
Bastion Host
Internal
Network
Perimeter
Network
Interior Router
Choke Router
CS262/0602/V2
Chapter 8 - 71
ADCS
Network Firewall
• Firewall Drawbacks
– Cannot protect attacks that don’t
go through firewall
– Cannot protect against data driven
attack – attacks in which
something is mailed or copied to
an internal host where it is then
executed e.g. firewall couldn’t
protect virus attack.
CS262/0602/V2
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ADCS
Traffic Controls
• Interceptors can tap all blocks of
message passing through
network.
• Can also determine who is
communicating frequently with
whom.
• Several techniques are done to
prevent interceptors from listening
to active traffic, such as:
• Pad Traffic
• Routing control
CS262/0602/V2
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ADCS
Traffic Controls
• Pad Traffic
– Deters a listener monitoring
messages from active links.
– Network generates spurious
(noise) messages to all computer
links to confuse the listener
– The noise will distorts the
information in the covert channel
– The intended host must be able to
recognize the messages as false
messages so that they will not
interfere with communication with
legitimate users
CS262/0602/V2
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ADCS
Traffic Controls
• Routing Control
– Routing control through specific
filter technology that allows
particular network address
passing through the gateway:
• Redirect messages – reroute
messages from A-C to go thru B
and ultimately to C. In this case
A-B (meaningful message) and
B-C (no value message)
• Periodically misroute
messages – changing an A-B
message into an A-C message.
B will experience missing
message
CS262/0602/V2
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ADCS
Traffic Controls
• Periodically delay a message
– to destroy the
synchronization between A-C.
Effective if channels depends
on the timing of message
– Note: Gateway – a device (has
processor and main memory) that
operates at transport level and above of
OSI model to connect more than 2
dissimilar n/w
CS262/0602/V2
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