VKSF 423 System Administration III

Authentication Kerberos

Announcements

Slight modification to the syllabus Office hours

Tuesday 10-12 Thursday 10-12, 2-3

Lab Three: Virtualized Storage Veritas Storage Central OpenAFS LVM or EVMS Dynamic Disks (MS DFS)

Syllabus Modifications

Old Component

Weight New Component

Due date

Labs 25% No change All sign offs and submission by the end of 10th week

Practical 25% No change Demonstrated before exam week begins

Group Presentation

10% In lab In lab approximately 5 minutes

Group Report

10% Site Book Due by end of 10th week

Homework 10% Group Evaluation

How did the individuals contribute to the completion of the labs

Final Exam 20% No change During the final exam period

Definitions

Identification- assertion of who you are

Authentication-process of proving one’s identity

Authorization-The privileges that accrue to an identity

Access control-Provide the correct services to the correct users

Two Types of Authentication

User authentication Machine to machine authentication

Cryptographic Other (weak)

Identification

Who are you? Who do you claim to be? Who are you acting as?

Authentication

Can you prove who you say you are?

How? Something you know

Passwords Something you are

Biometrics Something you have

Access tokens

Access Control

All of the above Allow the correct users

Into a system Access to appropriate resources

Disallow invalid users Entry to the systems Deny access to restricted resources

Something you KnowPasswords

Oxymoron: Large random string != easy to remember

Password design/assignment Multiple words/syllables Mixed case/digits/punctuation

Storage Weak/strong encryption

Users perceive the risks as minimal vs. need to get work done

Passwords

Myth: never write down a password Recovery Helps more complicated passwords Multiple passwords

Clues/questions One time passwords

Something you areBiometrics

Voice, retinal, DNA, body geometry, signature, finger prints

Hard to change Easy to forge

Something you haveAccess Tokens

Physical keys Smart cards Translators Problems

Stolen Duplicated Spoofed

Authentication Protocols

Cryptographic methods to authenticate over a network

Multiple vulnerabilities

Network Authentication Options

Do nothing- trust machine to prevent unauthorized user access (control physical access)

Require machine to prove identity to network, then trust machine to authenticate users and provide access control

Require identification and authentication at each resource

Authentication Requirements

Must be Secure A.k.a. secure enough to push hackers

elsewhere Must be reliable

Manageable level of false negatives and false positives

Transparent to users Scalable to enterprise networks

Simple Protocol

Bob enters password on client Client sends password to server Server looks up id and password in

database of ids and passwords If it matches, validation message

sent to client & Bob is in

Problems with simple scenario

Clear text password in database Clear text password in transfer Confirmation spoofing

Password Database

Hide Encrypt

Salt Multiple serial encryptions

Transfer

Hashing Encryption

Confirmation spoofing

Simple T/F Alternate hash of password/known

key Encryption

Improved Protocol: Challenge

Avoid clear text transfer of password Bob informs server of desire to

access Server offers a phrase to Bob Bob encrypts phrase with Bob’s

password and sends to server Server, who already knows Bob’s

password, also encrypts phrase with Bob’s password and compares

Problems with improved version

Server needs clear text copy of Bob’s password

Given enough instances of a login the original password could be determined

Use of a “Trusted Third Party”

The “Blind Date” protocol I don’t know Kathy She doesn’t know me We both know Loretta We both separately contact Loretta Loretta “vouches” for me to Kathy Loretta “vouches” for Kathy to me

Levels of Kerberos Protection

Authentication at initiation of network session, assume future messages from same address come from same machine

Authentication of each message, no encryption of message

Private messages-each message is authenticated and encrypted

Kerberos Modules

Applications library Encryption library Database library Database administration programs Administration server Authentication server Db propagation software User programs applications

Kerberos Misc.

Model based on Needham and Schroeder key distribution protocol

Encryption done with DES Extendable to DES Cypher Block Chaining

Database Contains one record/principal Record contains name, private key,

expiration date of principal Name- name.instance@realm

Kerberos

Ticket Used to securely pass the identity of the

person to whom the ticket was issued between the authentication server and the end server.

Authenticator Contains additional information which when

compared against the ticket proves that the client presenting the ticket is the same one to which the ticket was issued.

Kerberos

Keeps database of clients and private keys If client is user, key is encrypted

password Generates temporary private keys

(session keys) Session keys are given to two clients

to encrypt messages between them.

Kerberos Ticket

Ticket is good for a single server and a single client Contains name of the server Name of the client IP address of the client Timestamp Lifetime Random session key

Encrypted using the private key of the server for which the ticket will be used

May be used until lifetime expires

Kerberos Authenticator

Contains Name of the client Client’s IP address Client’s current time

Can only be used once, must be regenerated each time a client wants to use a service

Can be regenerated by the client (without going to the server)

Encrypted in the session key that is part of the ticket

Enhanced protocol: Kerberos

Bob asks K-server to access Mary’s server K-server checks to see if Bob has access

permissions K-server sends Bob a ticket and a

session key Bob uses session key to create an

authenticator to prove to Mary he is Bob Bob send ticket and authenticator to

Mary Mary checks both

Main Problem

Authentication of user or device given zero prior information

Does Kerberos do this?