CS 356 Lecture 28 Internet Authentication Spring 2013 Review - - PowerPoint PPT Presentation

CS 356 – Lecture 28 Internet Authentication

Spring 2013

Review

• Chapter 1: Basic Concepts and Terminology
• Chapter 2: Basic Cryptographic Tools
• Chapter 3 – User Authentication
• Chapter 4 – Access Control Lists
• Chapter 5 – Database Security (skipped)
• Chapter 6 – Malicious Software
• Networking Basics (not in book)
• Chapter 7 – Denial of Service
• Chapter 8 – Intrusion Detection
• Chapter 9 – Firewalls and Intrusion Prevention
• Chapter 10 – Buffer Overflow
• Chapter 11 – Software Security
• Chapter 12 – OS Security
• Chapter 22 – Internet Security Protocols
• Chapter 23 – Internet Authentication Applications

Chapter 23

Internet Authentication Applications

Kerberos Overview

• initially developed at MIT
• software utility available in both the public

domain and in commercially supported versions

• issued as an Internet standard and is the

defacto standard for remote authentication

• overall scheme is that of a trusted third party

authentication service

• requires that a user prove his or her identity

for each service invoked and requires servers to prove their identity to clients

Kerberos Protocol

• designed to counter a variety of threats to the security of a client/server dialogue
• obvious security risk is impersonation
• servers must be able to confirm the identities of clients who request service

involves clients, application servers, and a Kerberos server

• user initially negotiates with AS for identity verification
• AS verifies identity and then passes information on to an application server

which will then accept service requests from the client use an Authentication Server (AS)

• if client sends user’s password to the AS over the network an opponent could
• bserve the password
• an opponent could impersonate the AS and send a false validation

need to find a way to do this in a secure way

Authentication Server (AS) Ticket- granting Server (TGS)

r e q u e s t t i c k e t

• g

r a n t i n g t i c k e t

• nce per

user logon session

• 1. User logs on to

workstation and requests service on host.

• 3. Workstation prompts

user for password and uses password to decrypt incoming message, then sends ticket and authenticator that contains user's name, network address, and time to TGS. ticket + session key r e q u e s t s e r v i c e

• g

r a n t i n g t i c k e t ticket + session key

• nce per

type of service

• 4. TGS decrypts ticket and

authenticator, verifies request, then creates ticket for requested server.

Kerberos

• 5. Workstation sends

ticket and authenticator to server.

• 6. Server verifies that

ticket and authenticator match, then grants access to service. If mutual authentication is required, server returns an authenticator. r e q u e s t s e r v i c e p r

• v

i d e s e r v e r a u t h e n t i c a t

• r
• nce per

service session

Figure 23.1 Overview of Kerberos

• 2. AS verifies user's access right in

database, creates ticket-granting ticket and session key. Results are encrypted using key derived from user's password.

Kerberos Overview

Kerberos Realms

• a Kerberos environment consists of:

– a Kerberos server – a number of clients, all registered with server – a number of application servers, sharing keys with server

• this is referred to as a realm

– networks of clients and servers under different administrative

• rganizations generally constitute different realms
• if multiple realms:

– their Kerberos servers must share a secret key and trust the Kerberos server in the other realm to authenticate its users – participating servers in the second realm must also be willing to trust the Kerberos server in the first realm

Kerberos Realms

AS TGS Kerberos Client Realm A AS TGS Kerberos Server Realm B

• 1. request ticket for local TGS
• 2. ticket for local TGS

3 . r e q u e s t t i c k e t f

• r

r e m

• t

e T G S 4 . t i c k e t f

• r

r e m

• t

e T G S 5 request ticket for remote server 6 ticket for remote server

• 7. request remote service

Figure 23.2 Request for Service in Another Realm

Kerberos Versions 4 and 5

• Kerberos v4 is most widely used version
• improvements found in version 5:

– an encrypted message is tagged with an encryption algorithm identifier

• this enables users to configure Kerberos to use an

algorithm other than DES

– supports authentication forwarding

• enables a client to access a server and have that

server access another server on behalf of the client

• supports a method for interrealm authentication that

requires fewer secure key exchanges than in version 4

Kerberos Performance Issues

• see larger client-server installations
• Kerberos performance impact in a large-scale

Kerberos security is best assured by placing the Kerberos server on a separate, isolated machine

• motivation for multiple realms is administrative, not

performance related

environment:

• very little if system is properly configured
• tickets are reusable which reduces traffic

Certificate Authority (CA)

certificate consists of:

• a public key plus a User ID of the key owner
• signed by a trusted third party
• typically the third party is a CA that is trusted by the user community

(such as a government agency or a financial institution)

user can present his or her public key to the authority in a secure manner and obtain a certificate

• user can then publish the certificate
• anyone needing this user’s public key can obtain the certificate and

verify that it is valid by way of the attached trusted signature

X.509 Authentication Service

universally accepted standard for formatting public-key certificates part of CCITT X.500 directory service standards uses public-key crypto & digital signatures

• widely used in network

security applications, including IPsec, SSL, SET, and S/MIME

• algorithms not

standardized, but RSA recommended

X.509 Certificates

Certificate Serial Number Version Issuer Name Signature algorithm identifier Subject Name Extensions Issuer Unique Identifier Subject Unique Identifier

algorithm parameters not before

algorithms parameters key algorithms parameters encrypted hash (a) X.509 Certificate

not after

Subject's public key info Signature

Figure 23.3 X.509 Formats

Period of validity

Version 1 Version 2 Version 3 all versions

Issuer Name This Update Date Next Update Date ! ! ! Signature algorithm identifier

algorithm parameters user certificate serial #

(b) Certificate Revocation List

revocation date

algorithms parameters encrypted hash

Signature Revoked certificate

user certificate serial # revocation date

Revoked certificate

Public Key Infrastructure X.509 (PKIX)

End entity certificate/CRL retrieval certificate publication certificate/CRL publication CRL publication cross certification Certificate/CRL Repository Certificate authority Registration authority Certificate authority registration, initialization, certification, key pair recovery, key pair update revocation request PKI users PKI management entities CRL issuer

Figure 23.4 PKIX Architectural Model

PKIX Management Functions

registration initialization certification key pair recovery key pair update revocation request cross certification

Federated Identity Management

• use of common identity management scheme

– across multiple enterprises and numerous applications – supporting many thousands, even millions of users

• principal elements are:

– authentication, authorization, accounting, provisioning, workflow automation, delegated administration, password synchronization, self-service password reset, federation

Identity Management

Principal Principal Administrator Administrator Data consumer

Identity control interface Principals provide attributes Principals authenticate, manage their identity elements Administrators provide attributes Data consumers apply references to obtain attribute data Data consumers obtain identifiers, attribute references

Identity Provider

Figure 23.5 Generic Identity Management Architecture

Attribute locator Principal authentication Identifier translation

Data consumer Attribute service Attribute service Attribute service Principal

Standards Used

Extensible Markup Language (XML)

characterizes text elements in a document

• n

appearance, function, meaning, or context

Simple Object Access Protocol (SOAP)

for invoking code using XML over HTTP

WS-Security

set of SOAP extensions for implementing message integrity and confidentiality in Web services

Security Assertion Markup Language (SAML)

XML-based language for the exchange

• f security

information between

• nline

business partners

Federated Identity Management

User store

(a) Federation based on account linking (b) Chained Web Services

Figure 23.6 Federated Identity Scenarios

Workplace.com (employee portal)

Name Joe Jane Ravi ID 1213 1410 1603

User store

Name Joe Jane Ravi ID 1213 1410 1603 Links: health benefits etc.

Health.com Workplace.com End user (employee) Initial authentication

User store

(b) Federation based on roles

W orkplace.com (employee portal)

Name Joe Jane Ravi ID 1213 1410 1603 Dept Eng Purch Purch

User store

Role Engineer Purchaser Links: parts supplier etc.

PartsSupplier.com Welcome Joe!

Technical doc. Troubleshooting

End user (employee) Initial authentication

Procurement application End user Soap message Initial message authentication Soap message

PinSupplies.com

Purchasing Web service

E-ship.com

Shipping Web service

Summary

• Kerberos
• Kerberos protocol
• Kerberos realms
• Kerberos versions 4

and 5

• Kerberos

performance issues

• X.509
• public-key

infrastructure

• PKIX management

functions

• PKIX management

protocols

• federated identity

management