FIREWALLS & NETWORK SECURITY with Intrusion Detection and VPNs, 2nd ed.

10Authenticating Users

By Whitman, Mattord, & Austin © 2008 Course Technology

Learning Objectives

Explain why authentication is a critical aspect of network security

Explain why firewalls authenticate and how they identify users

Describe user, client, and session authentication List the advantages and disadvantages of popular

centralized authentication systems Discuss the potential weaknesses of password

security systems Discuss the use of password security tools Describe common authentication protocols used by

firewalls Slide 2Firewalls & Network Security, 2nd ed. - Chapter 10

The Authentication Process in General

The act of identifying users and providing network services to them based on their identity

Two forms– Local authentication

– Centralized authentication service (often uses two-factor authentication)

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How Firewalls Implement the Authentication Process

1. Client makes request to access a resource2. Firewall intercepts the request and prompts

the user for name and password3. User submits information to firewall4. User is authenticated5. Request is checked against firewall’s rule

base6. If request matches existing allow rule, user is

granted access7. User accesses desired resources

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How Firewalls Implement the Authentication Process (continued)

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Firewall Authentication Methods

User authentication Client authentication Session authentication

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User Authentication

Basic authentication; user supplies username and password to access networked resources

Users who need to legitimately access your internal servers must be added to your access control lists (ACLs)

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User Authentication (continued)

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Client Authentication

Same as user authentication but with additional time limit or usage limit restrictions

When configuring, set up one of two types of authentication systems– Standard sign-on system

– Specific sign-on system

Slide 9Firewalls & Network Security, 2nd ed. - Chapter 10

Client Authentication (continued)

Slide 10Firewalls & Network Security, 2nd ed. - Chapter 10

Session Authentication

Required any time the client establishes a session with a server of other networked resource

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Comparison of Authentication Methods

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Centralized Authentication

Centralized server maintains all authorizations for users regardless of where user is located and how user connects to network

Most common methods– Kerberos

– TACACS+ (Terminal Access Controller Access Control System)

– RADIUS (Remote Authentication Dial-In User Service)

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Process of Centralized Authentication

Slide 14Firewalls & Network Security, 2nd ed. - Chapter 10

Kerberos

Provides authentication and encryption through standard clients and servers

Uses a Key Distribution Center (KDC) to issue tickets to those who want access to resources

Used internally on Windows 2000/XP Advantages

– Passwords are not stored on the system– Widely used in UNIX environment; enables

authentication across operating systems

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Kerberos Authentication

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TACACS+

Latest and strongest version of a set of authentication protocols for dial-up access (Cisco Systems)

Provides AAA services– Authentication– Authorization– Auditing

Uses MD5 algorithm to encrypt data

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RADIUS

Centralized dial-in authentication service that uses UDP

Transmits authentication packets unencrypted across the network

Provides lower level of security than TACACS+ but more widely supported

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TACACS+ and RADIUS Compared

Strength of security Filtering characteristics Proxy characteristics NAT characteristics

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Strength of Security

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Filtering Characteristics

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Proxy Characteristics

RADIUS– Doesn’t work with generic proxy systems, but a

RADIUS server can function as a proxy server TACACS+

– Works with generic proxy systems

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NAT Characteristics

RADIUS– Doesn’t work with NAT

TACACS+– Should work through NAT systems

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Password Security Issues

Passwords that can be cracked (accessed by an unauthorized user)

Password vulnerabilities Lax security habits

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Passwords That Can Be Cracked

Ways to crack passwords– Find a way to authenticate without knowing the

password– Uncover password from system that holds it– Guess the password

To avoid the issue– Protect passwords effectively– Observe security habits

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Password Vulnerabilities

Built-in vulnerabilities– Often easy to guess– Often stored visibly– Social engineering

To avoid the issues– Choose complicated passwords– Memorize passwords– Never give passwords out to anyone

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Lax Security Habits

To maintain some level of integrity, draw up a formal Memorandum of Understanding (MOU)

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Password Security Tools

One-time password software Shadow password system

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One-Time Password Software

Password is generated using a secret key Password is used only once, when the user

authenticates Different passwords are used for each

authentication session Types

– Challenge-response passwords– Password list passwords

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Shadow Password System

A feature of Linux that stores passwords in another file that has restricted access

Passwords are stored only after being encrypted by a randomly generated value and an encoding formula

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Other Authentication Systems

Single-password systems One-time password systems Certificate-based authentication 802.1x Wi-Fi authentication

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Single-Password Systems

Operating system password Internal firewall password

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One-Time Password Systems

Single Key (S/Key) SecurID Axent Pathways Defender

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Single Key (S/Key)

Uses multiple-word rather than single word passwords– User specifies single-word password and the

number of times it is to be encrypted– Password is processed by a hash function n

times; resulting encrypted passwords are stored on the server

Never stores original password on the server

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SecurID

Uses two-factor authentication– Physical object

– Piece of knowledge Most frequently used one-time password

solution with FireWall-1

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SecurID Tokens

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Axent Pathways Defender

Uses two-factor authentication and a challenge-response system

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Certificate-Based Authentication

FireWall-1 supports the use of digital certificates to authenticate users

Organization sets up a public key infrastructure (PKI) that generates keys to users– User receives a code (public key) that is

generated using the server’s private key and uses the public key to send encrypted information to the server

– Server receives the public key and can decrypt the information using its private key

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802.1x Wi-Fi Authentication

Supports wireless Ethernet connections Not supported by FireWall-1 802.1x protocol provides for authentication of

users on wireless networks Wi-Fi uses Extensible Authentication Protocol

(EAP)

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Wireless Authentication

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Chapter Summary

Overview of authentication and its importance to network security

How and why firewalls perform authentication services

Types of authentication performed by firewalls– User

– Client

– Session

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Chapter Summary (continued)

Generally, users supply:– Something they have (such as a smart card) or– Something they know (such as a password) or– Both

Latest authentication systems measure or evaluate a physical attribute, such as a fingerprint or voiceprint

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Chapter Summary (continued)

In a centralized authentication system:– Firewall works with an authentication server– Authentication server handles

• Username and password maintenance/generation• Login requests• Auditing

Examples of centralized authentication systems:– Kerberos– TACACS+– RADIUS

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Chapter Summary (continued)

Passwords– Important part of virtually every authentication

system– Take one of two general forms:

• Single-word– User password compared against database of

passwords; access granted if match is made– Vulnerable to ability of hackers to determine

passwords, to user error, and to bad security habits• One-time passwords

– Generated dynamically each time user attempts to log on to network

– Secret key used to generate single- or multiple-word password

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