Transcript Chapter 19

Chapter 19:
Computer and Network Security
Techniques
Business Data Communications, 6e
IPSec Functions
• Authentication Header (AH)
• Encapsulating Security Payload (ESP)
• Key exchange
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ESP Transport and Tunnel Mode
• Transport mode: provides protection
primarily for upper-layer protocols.
Typically used for end-to-end
communications between two hosts.
Payload is encrytped but not the header.
• Tunnel mode: provides protection for the
entire IP packet. The entire packet is
placed within a new outer IP packet. Used
when one destination is a security gateway. 3
Scope of ESP Encryption and
Authentication
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Key Management
• Manual: system administrator manually
configures each system with its own keys
and with the keys of other communicating
systems.
• Automatic: An automated system enables
the on-demand creation of keys and
facilitates the use of keys. Used in large
system configurations.
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Advantages of IPSec
• Provides managers with a standard means
of implementing security for VPNs.
• Encryption and authentication algorithms
and security protocols are well studied.
• Users can be confident that IPSec provides
strong security.
• Can be implemented in firewalls and
routers owned by the organization, giving
network managers control over security.
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SSL Architecture
• Provides reliable end-to-end secure service.
• Uses two layers of protocols.
• SSL Record Protocol provides basic security
services to higher layer protocols such as HTTP
• SSL includes:
-Handshake Protocol
-Change Cipher Spec Protocol
-Alert Protocol
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SSL Protocol Stack
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Key SSL Concepts
• Connection: a transport that provides a
suitable type of service. Every connection
is associated with one session.
• Session: an association between client and
server. Defien a set of sryptographic
security parameters which can be sharedby
multiple connections.
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SSL Record Protocol Operation
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SSL Protocols
• Change Cipher Spec Protocol: simplest
protocol, consists of a single byte with a
value of 1; causes the pending state to be
copied into the current state.
• Alert Protocol: used to convey SSL
related alerts to the peer entity. Each
message consisst of 2 bytes; the first
denotes a warning or fatal error.
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Handshake Protocol
• The most complex part of SSL.
• Allows for servers and clients to
authenticate each other, negotiate an
encryption and MAC algorithm and
cryptographic keys to protect data.
• Used before any application data is
transmitted.
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Handshake Protocol Phases
• Phase 1: Initiates logical connection
• Phase 2: passes certificate, additional key
information and request for client certificate.
Also passes server-done message.
• Phase 3: client sends message to server
depending on underlying public-key scheme.
• Phase 4: completes setting up the secure
connection.
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802.11i Operational Phases
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802.11i Architecture
• Authentication: protocol used to define an
exchange between a user and an AS
• Access control: function that enforces the use of
the authentication function, routes messages
properly and facilitates key exchange.
• Privacy with message integrity: MAC-level
data are encrypted along with a message integrity
code that ensures that the data have not been
altered.
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802.11i Access Control
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Intrusion Detection
• Security Intrusion: a security event, or a combination of
multiple security events, that constitutes a security incident in which
an intruder gains, or attempts to gain, access to a system (or system
resource) without having authorization to do so.
• Intrusion Detection: A security service that monitors and
analyzes system events for the purpose of finding and providing realtime or near-real-time warning of, attempts to access system
resources in an unauthorized manner.
• Intrusion Detection System Classification:
-Host-based IDS
-Network-based IDS
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IDS Logical Components
• Sensors
• Analyzers
• User Interface
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Approaches to Host-Based IDSs
• Anomaly Detection: involves the collection
of data relating to the behavior of legitimate users
over time.
-Threshold Detection
-Profile based
• Signature Detection: involves an attempt to
define a set of rules or attack patterns that can be
used to decide an intruders behavior.
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Firewalls
• Provides an additional layer of defense
between internal systems and external
networks
• Firewalls use four techniques:
-Service Control
-Direction Control
-User Control
-Behavior Control
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Firewall Capabilities
• Defines a single choke point that keeps
unauthorized users out of the protected
network.
• Provides a location for monitoring
security-related events.
• Provides a platform for several Internet
functions.
• Serves as a platform for IPSec.
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Firewall Limitations
• Cannot protect against attacks that bypass
the firewall.
• May not protect against all internal threats.
• A wireless LAN may be accessed from
outside.
• A client (Laptop, PDA, portable storage
device, etc) may be infected outside and
then attached internally
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Firewall Types
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Antivirus Approaches
• Prevention: Do not all the virus to get into the
system.
• Detection: Once infection has occurred,
determine that it has occurred and locate the
virus.
• Identification: Once detection has been
achieved, identify the specific virus that has
infected a program.
• Removal: Remove all traces of the virus and
restore the program to its original state.
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Generic Decryption
• Enables antivirus programs to detect
complex polymorphic viruses.
• Generic Decryption elements:
-CPU emulator
-Virus signature scanner
-Emulation control module
• The most difficult design issue is to
determine how long to run the scanner.
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Digital Immune System
• Developed first by IBM, then refined by
Symantec.
• Provides a general purpose emulation and
virus detection system.
• Detects new viruses, analyze them, adds
detection and shielding for it, removes it
and passes information on about that virus
to other systems.
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Digital Immune System
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Behavior Backbone Software
• Integrates with the operating system and
monitors program behavior in real-time for
malicious actions.
• Blocks potentially malicious actions.
• Suspicious software is also blocked.
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Behavior-Blocking Software
Operation
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Requirements for Worm
Countermeasures
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Generality
Timeliness
Resiliency
Minimal denial-of-service costs
Transparency
Global and local coverage
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Classes of Worm Defense
• Signature-based worm scan filtering
• Filter-based worm containment
• Payload-classification-based worm
containment
• Threshold random walk (TRW) scan
detection
• Rate limiting
• Rate halting
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