Transcript Chapter 24 - William Stallings, Data and Computer

Data and Computer
Communications
Chapter 24 – Computer and Network
Security Techniques
Ninth Edition
by William Stallings
Data and Computer Communications, Ninth
Edition by William Stallings, (c) Pearson
Education - Prentice Hall, 2011
Computer and Network Security
Techniques
To guard against the baneful influence exerted by
strangers is therefore an elementary dictate of savage
prudence. Hence before strangers are allowed to enter a
district, or at least before they are permitted to mingle
freely with the inhabitants, certain ceremonies are often
performed by the natives of the country for the purpose of
disarming the strangers of their magical powers, or of
disinfecting, so to speak, the tainted atmosphere by which
they are supposed to be surrounded.
—The Golden Bough
Sir James George Frazer
—The Art of War
Sun Tzu
Virtual Private Networks and
IPSEC
 IPSEC



provides three main facilities:
an authentication-only function called the
Authentication Header (AH)
combined authentication/encryption function
called Encapsulating Security Payload (ESP)
key exchange functionality
Transport & Tunnel Modes
 ESP

supports two modes of use:
Transport
• which provides protection for upper-layer protocols
• typically used for end-to-end communication
between two hosts

Tunnel
• which provides protection to the entire IP packet
• used when at least one of the two ends is a
security gateway
ESP Encryption and
Authentication
Example of Tunnel Mode
Host A
IPSEC
Processing
Needed?
Outer IP
Header is
Stripped
Host B
Key Management
 IPSEC
key management involves the
determination and distribution of secret
keys.
IPSEC supports 2 types of key management
• Manual – requires a system administrator to
manually configure the systems and
corresponding keys
• Automated – no human intervention needed
and enables on-demand creation of keys
IPSEC and VPNs
 there
is a driving need for users and
organizations to be able to:


secure their networks
receive traffic over the internet while still
meeting the need to secure the network
Ipsec and VPNs
IPsec
provides the • can be implemented in
routers or firewalls owned
network
and operated by the
manager
organization
with
• a service provider can
simplify the job of planning,
complete
implementing, and
control over
maintaining Internet-based
the security
VPNs for secure access and
aspects of
secure communication
VPN
Application layer security

SSL – Secure Socket
Layer


general purpose service
designed to provide a
reliable end-to-end secure
service
set of protocols that relies
on TCP
• could be provided as part of
the underlying protocol suite
and transparent to
applications
• can be embedded in specific
packages

TLS – Transport
Layer Security


RFC 2246
basically an updated
service from SSL that
provides reliable endto-end secure data
transfer
SSL Architecture
(Two Important SSL
Concepts)
SSL Connection
• transport that provides a suitable type
of service
• peer-to-peer and transient
SSL Session
• association between client and server
• created by handshake protocol
SSL Record Protocol
MAC= message authentification code
Change Cipher Spec Protocol
(see Fig. 24.2 shown previously)
 the
simplest of the three SSL-specific
protocols
 makes use of the SSL Record Protocol
 consists of a single message, which
consists of a single byte with the value 1

sole purpose is to cause the pending state to
be copied into the current state
Alert and Handshake
Protocols (see Fig. 24.2 shown previously)
 Alert


Protocol (ex. Incorrect MAC)
conveys SSL related alerts to the peer entity
compressed and encrypted
 Handshake




Protocol
most complex part of SSL
allows server and client to authenticate
negotiates encryption and MAC algorithm as
well as the keys
used before the transmission of any
application data
Wi-Fi Protected Access
 Wi-Fi
Protected Access is also known as
WPA
 is the Wi-Fi standard

a set of security mechanisms created to
accelerate the introduction of
strong security into WLANs
WPA

Based on the IEEE
802.11i standard
 addresses 3 main
security areas
Authentication
Key management
Data transfer privacy

requires the use of an
Authentication Server
(AS)


PSK (pre-shared key)
does not require an
AS
defines a more robust
authentication
protocol
 Supports AES with
128-bit keys and 104bit RC4 encryption
802.11i Operational Phases
3 Main Ingredients for WPA
Access
Control
802.11i Access Control
Privacy with Message Integrity
 IEEE
80211i defines two schemes
 both add a message integrity code (MIC)
to the 802.11 MAC Frame
Temporal Key Integrity Protocol (TKIP)
• WPA-1
• only requires software changes to devices
implemented with WEP
Counter Mode – CBC MAC Protocol (CCMP)
• WPA-2
• makes use of AES protocol
Intrusion Detection
Intrusion Detection
 RFC

2828
Security Intrusion
• a security event, or combination of multiple
security events, that constitutes a security incident
in which an intruder gains, or attempts to gain
access to a system without having authorization to
do so

Intrusion Detection
• a security service that monitors and analyzes
system events for the purpose of finding, and
providing real-time or near-real-time warning of,
attempts to access system resources in an
unauthorized manner
Intrusion Detection (IDS)
IDS
Host Based
monitors
characteristics of
events on a single
host
network based
monitors
characteristics of
events on the
network
IDS Components
Sensors
• collect data
Analyzers
User Interface
• analyze the
collected data to
see if an intrusion
has occurred
• enables a user to
view the sensor
output and the
completed
analysis output
Basic Principles of Countering
Intrusions
Intruder Behavior Profiling
Host-Based IDS Techniques
 can
detect both external and internal
intrusions.
Anomaly Detection
• collecting a baseline
and then comparing
behavior against that
baseline
Signature
Detection
• defines a set of rules
or attack patterns
Firewalls
integral part of an organization’s
defense-in-depth strategy as well as an
important complement to an organization’s
IDS.
 typically thought of as perimeter protection
 “defense in depth”
 an
Firewall Characteristics
 all
traffic passes through the firewall
 only
authorized traffic is allowed to pass
 the firewall itself is immune to penetration

assumes a hardened system with a secured
operating system
Firewall Control Access
Techniques
Service Control
• determines types of internet services that can be accessed both
inbound and outbound
Direction Control
• determines the direction in which particular service requests may be
initiated
User Control
• access to service is controlled based on user’s identity
Behavior Control
• controls how a particular service can be used
Firewall Limitations
 cannot
protect against attacks that bypass
the firewall (i.e. a modem pool)
 may not fully protect against internal
threats
 cannot guard against wireless
communications between local systems on
different sides of the internal firewall
 cannot protect against mobile devices that
plug directly into the internal network
Types of Firewalls
Packet Filtering Firewall
• applies a set of rules to
each incoming and
outgoing IP packet
Stateful Inspection Firewall
• tightens up the rules for
TCP traffic by creating a
directory of outbound
TCP connections.
Application Level Gateway
• application proxy, acts as
a relay of application
level traffic
Circuit Level Gateway
• sets up two TCP
connections and relays
TCP segments from one
connection to the other
Types of
Firewalls
PacketFiltering
Examples
Packet Filtering Firewalls
 Advantages:



its simplicity
transparent to users
very fast
 Disadvantages:

cannot prevent attacks to application specific
vulnerabilities
 do not support advanced user authentication schemes
 vulnerable to attacks that take advantage of problems
within TCP/IP
 susceptible to security breaches caused by improper
configurations
Stateful Firewall Connection
State Table
(keeps track of sequence number and other info)
Application-Level Gateway
 also
called an application proxy, acts as a
relay of application-level traffic
 tend to be more secure than packet filters
 easy to log and audit all incoming traffic
 Disadvantage:

additional processing overhead on each
connection
Circuit-Level Gateway
 circuit-level
proxy
 stand alone system or function performed
by an application-level gateway
 sets up two TCP connections
 security function consists of determining
which connections will be allowed
 used where the system administrator
trusts the internal users
Malware Defense
 Prevention
is the primary goal for malware
defense. However when prevention is not
possible we want to:



Detect
Identify
Remove
 Anti-virus
the above
software is designed to do all of
Anti-Virus Generic Decryption
(GD)
 GD
is technology that enables anti-virus
programs to detect even the most complex
polymorphic viruses.
A GD scanner contains:
• CPU Emulator
• Virus Signature Scanner
• Emulation Control Module
Digital Immune System
Behavior-Blocking Software
Types of behavior being
monitored are:

integrates with the
operating system of a
host computer and
monitors program
behavior in real time.
• attempts to open, view,
delete or modify files
• attempts to format or
otherwise erase disks
• modifications to the logic of
macro or executable files
• modifications of critical
system settings
• unauthorized scripting
Behavior Blocking
Generality
Timeliness
• should be able to
handle a wide variety of
worm attacks
• approach should
respond quickly to limit
infected systems
Resiliency
Minimal denial-ofservice costs
• should be resistant to
techniques by to evade
worm
Transparency
• should not require
modification to existing
OS and hardware
• minimal reduction in
capacity or service due
to countermeasure
Global and local
coverage
• should be able to deal
with attack sources
from inside and outside
(6 Classes of Worm Defense)
 Signature-based
scanning & filtering
 Filter-based containment
 Payload-classification based worm
containment
 Threshold Random Walk (TRW) scan
detection
 Rate Limiting
 Rate Halting
Summary
 VPNs

transport and tunnel modes
 SSL

and TLS
architecture and protocol
 Wi-Fi

and IPsec
protected access
access control and privacy
 Intrusion
detection
 Firewalls

characteristics and types
 Malware

Defense
worm countermeasures