Authenticating Users Chapter 6

Learning Objectives Understand why authentication is a critical aspect of network security Describe why firewalls authenticate and how they identify users Describe user, client, and session authentication List advantages and disadvantages of popular centralized authentication systems continued

Learning Objectives Be aware of potential weaknesses of password security systems Understand the use of password security tools Be familiar with common authentication protocols used by firewalls

The Authentication Process in General The act of identifying users and providing network services to them based on their identity Three forms  Basic authentication  Challenge-response authentication  Centralized authentication service (often uses two-factor authentication)

How Firewalls Implement the Authentication Process 1.

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Client makes request to access a resource Firewall intercepts the request and prompts the user for name and password User submits information to firewall User is authenticated Request is checked against firewall’s rule base If request matches existing allow rule, user is granted access User accesses desired resources

How Firewalls Implement the Authentication Process

Types of Authentication with Firewalls User authentication Client authentication Session authentication

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)

User Authentication

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

Client Authentication

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

Comparison of Authentication Methods

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)

Process of Centralized Authentication

Kerberos Authentication 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

Kerberos Authentication

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

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

TACACS+ and RADIUS Compared Strength of security Filtering characteristics Proxy characteristics NAT characteristics

Strength of Security

Filtering Characteristics

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

NAT Characteristics RADIUS  Doesn’t work with NAT TACACS+  Should work through NAT systems

Password Security Issues Passwords that can be cracked (accessed by an unauthorized user) User error with passwords Lax security habits

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

User Error with Passwords 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

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

Password Security Tools One-time password software Shadow password system

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

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

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

Single-Password Systems Operating system password Internal firewall password

One-Time Password Systems Single Key (S/Key) SecurID Axent Pathways Defender

Single Key (S/Key) Password Authentication 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

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times; resulting encrypted passwords are stored on the server Never stores original password on the server

SecurID Password Authentication Uses two-factor authentication  Physical object  Piece of knowledge Most frequently used one-time password solution with FireWall-1

SecurID Tokens

Axent Pathways Defender Password Authentication Uses two-factor authentication and a challenge-response system

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

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)

802.1x Wi-Fi Authentication

Chapter Summary Overview of authentication and its importance to network security How and why firewalls perform authentication services Types of authentication performed by firewalls  Client  User  Session continued

Chapter Summary Centralized authentication methods that firewalls can use   Kerberos TACACS+  RADIUS Password security issues and special password security tools Authentication protocols used by full-featured enterprise-level firewalls