K E R B E R O S

GROUP: ACES

I N T R O D U C T I O N

S A R A M A L I K

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DEFINITION-KERBEROS

“Kerberos The name is taken from Greek mythology; Kerberos was a three-headed dog who

guarded the gates of Hades. is a network authentication protocol. It is designed

to provide strong Authentication for client/server applications by using

secret-key cryptography. “

1- It is secure.

2- It never sends a password unless it is encrypted.

WHAT IS KERBEROS?

• Network authentication

protocol

• Developed at MIT in the

mid 1980s

• Available as open source

or in supported

commercial software

ARCHITECTURE:

It consists of the following 3 components:

1-Client

2-Authentication server or key distribution server(KDC)

3- Server

And has 3 main exchanges:

1-Authentication Service(AS) Exchange

2-Ticket Granting Service(TGS) Exchange

3- Client Server (CS) Exchange.

WHY KERBEROS?

• Sending usernames and passwords in the clear jeopardizes the security of the network.

• Each time a password is sent in the clear, there is a chance for interception.

• Uses Needham-Schroeder Algorithm.

NEEDHAM-SHROEDER PROTOCOL:

Needham-Schroeder Protocol:

• The NSP symmetric key establishes a session key to protect further communication.

• The NSP key protocol provides mutual authentication.

FIREWALL VS. KERBEROS?

• Firewalls make a risky assumption:

that attackers are coming from the

outside. In reality, attacks

frequently come from within.

• Kerberos assumes that network

connections (rather than servers

and work stations) are the weak

link in network security.

DESIGN REQUIREMENTS

• Interactions between hosts and clients should be encrypted.

• Must be convenient for users (or they won’t use it).

• Protect against intercepted credentials.

CRYPTOGRAPHY APPROACH

• Private Key: Each party uses the same secret key to encode and

decode messages.

• Uses a trusted third party which can vouch(verify) for the

identity of both parties in a transaction. Security of third party

is imperative.

HOW DOES KERBEROS WORK?

• Instead of client sending password to

application server:

– Request Ticket from authentication server

– Ticket and encrypted request sent to

application server

• How to request tickets without

repeatedly sending credentials?

– Ticket granting ticket (TGT)

ABBREVIATION USED:

• AS: Authentication Server

• KDC: Key distribution Center

• TGS: Ticket Granting Server

• SS: Service server

• TGT: Ticket granting ticket

HOW DOES KERBEROS WORK?: TICKET GRANTING TICKETS

WEAKNESSES AND SOLUTIONS

If TGT stolen, can be used to access network services.

Only a problem until ticket expires in a few hours.

Subject to dictionary attack. Timestamps require hacker to guess in 5 minutes.

Very bad if Authentication Server compromised.

Physical protection for the server.

COMPETITOR-SSL:

Secure Sockets Layer:

SSL (Secure Sockets Layer) is a standard security technology for establishing an

encrypted link between a server and a client—typically a web server (website) and a

browser; or a mail server and a mail client (e.g., Outlook).

THE COMPETITION: SSL

SSL Kerberos

Uses public key encryption Uses private key encryption

Is certificate based (asynchronous) Relies on a trusted third party

(synchronous)

Ideal for the WWW Ideal for networked environments

Key revocation requires Revocation

Server to keep track of bad

certificates

Key revocation can be accomplished by

disabling a user at the Authentication

Server

Certificates sit on a users hard drive

(even if they are encrypted) where

they are subject to being cracked.

Passwords reside in users' minds where

they are usually not subject to secret

attack.

Uses patented material, so the

service is not free. Netscape has a

profit motive in wide acceptance of

the standard.

Kerberos has always been open source

and freely available.

P R O T O C O L S

Z O Y A A L A M G I R

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•Needham-Schroeder protocol

KERBEROS 4

•Host difference

DIFFERENCE

KERBEROS 5

•Based on kerberos 4

•Differences

KERBEROS 5

• Ticket:the ticket can only be decrypted by the

service, as it is encrypted with the

service’s encryption key

• Reply:

encryption type of the reply from the

KDC to the client refers to the part of

the reply encrypted with the user’s

encryption key.

MAIN FEATURES

• Session key

. This key is a sharing between the

client and the server so here needed

to have that type encryption key that

is supported by both client support

and service

CONT…

•Forward able tickets

•Proxiable tickets

•Renewable tickets

•Postdated tickets

TICKET OPTIONS

• Decryption of the service ticket with the service’s key

• Extraction of the session key contained inside

• Creation of a new Kerberos 4 ticket for the same service

and client

• Pasting in the session key from the original Kerberos 5

ticket.

KERBEROS 5-TO-4 TICKET TRANSLATION

•Client is unable to get an initial “Ticket Granting Ticket”.

•Client possesses a valid TGT but faces some error prior to the achievement of a service ticket.

•Client possesses a valid TGT and has acquired service ticket, but faces error upon connection to the Kerberoizedservice.

TROUBLESHOOTING

•Errors Obtaining an Initial Ticket

•Unsynchronized Clocks

ERRORS AND SOLUTIONS

S E C U R I T Y

S O N I A R A S H E E D

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KERBEROS

• The most popular cross-platform, network-wide authentication system

• Kerberos is extremely secure in a theoretical sense.

• Kerberos provides authentication, authorization and auditing services.

• Implemented only authentication services

KERBEROS AUTHENTICATION (REVIEW)

KERBEROS SECURITY

• It by no means has a perfect security record.

• Implementation of Kerberos on your network does not guarantee perfect security.

• It does not prevent compromises caused:

buggy server software

administrators granting permissions to unauthorized users

poorly chosen passwords

etc.

KERBEROS ATTACKS

Some electronic attacks that can compromise the security of your Kerberos system:

1. Root compromise of a Kerberos KDC machine:

A root-level compromise of a KDC machine gives the attacker full control over the entire

Kerberos authentication system.

2. Compromise of a Kerberos administrator’s credentials:

If an attacker obtains the password of a Kerberos administrative principal, then the

attacker can get complete access to the entire Kerberos database.

KERBEROS ATTACK (CONT…)

3. Root compromise of a server machine:

The attacker can impersonate this service and also decrypt the encrypted traffic sent

between clients and the compromised service.

4. Compromise of user credentials:

Two Scenario:

a. user’s credential (ticket) cache exposed

b. user’s password is compromised

OTHER ATTACKS

1. Denial of service:

• Attack against your organization’s KDCs by flooding them with authentication

requests.

• Kerberos cannot protect against denial of service attacks .

• Recommendations:

Network Should be firewalled

Additional KDCs for network can overcome the effects of a DoS attack.

OTHER ATTACKS(CONT…)

2.The “insider”:

• Does not protect against an internal authorized user who decides to misuse their

privileges.

• For example:

A rogue Kerberos administrator

3. Social engineering and password exposure

4. Security holes in the Kerberos software itself

PROTOCOL SECURITY ISSUES

REPLAY ATTACK:

PROTOCOL SECURITY ISSUES(CONT…)

• Dictionary and Brute-Force Attacks:

Password guessing" attacks are not solved by Kerberos.

• Man-in-the-Middle Attacks:

Built-in protection against man-in-the-middle attacks.

Kerberos performs mutual authentication

• Mutual Authentication:

SECURITY SOLUTIONS

• Requiring Pre-Authentication:

• Enforcing Secure Passwords

• Enforcing Password Lifetimes and History:

APPLICATION

• CIFS remote file access: Common Internet File System (CIFS) is the new name of

Microsoft's SMB protocol that is mainly used for file and print sharing.

• Secure dynamic DNS update

• Distributed File System Management

• Host to Host IPsec

• Secure internet Web services

• Authenticate certificate request to certification authority (CA)

K E R B E R O S

F U T U R E

A Q S A G I L L A N I

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KERBEROS FUTURES

• Kerberos developing to integrate new technologies and to prevent new

threats.

• Kerberos working group developed extensions to Kerberos 5 protocol

for using Kerberos in future.

• New developments related to Kerberos, used in future summarised

below:

PROJECT MOONSHOT

• This project is a JANET(UK)-led initiative.

• It is to develop a single technology for benefits of non-Web services.

• including high Performance Computing and other services i-e mail, file store, remote access and instant messaging.

• The goal is to access broad range of services and applications.

• This is to improve delivery of services by providing users with a common single sign-on for both.

•

• Service providers offer services to users using a single common

authentication mechanism.

• This enhance the user’s experience.

• Reduce costs for organisations delivering services.

• The protocol used for authentication and encryption key management,

in moonshot is Kerberos.

SMART CARDS:

• What is?

• Smart card is a small, tamperproof computer.

• Smart card contains a CPU and some non-volatile storage to keep secrets, such

as private keys.

• Smartcards makes impact on current computer systems because of

security.

• Smart card market grow from 544 million Unit in 1995 to 3.4 billion

units by 2001.

HOW CAN SMARTCARDS HELP KERBEROS?

• Problems of Kerberos are not solvable without special-purpose

hardware, no matter what the design of the protocol.

• The problems include:

• _ Need for secure encrypssstion device

• _ Need for secure key storage

• _ Dictionary attack on passwords

SMART CARD INTEGRATION:

• Store user key in a smartcard, load key into a workstation, and use it for

decrypting TGT instead of key from a password.

• 2. Decrypt TGT in a smartcard.

• Method 1 is not secure as method 2 becz user key loaded in a

workstation. If workstation is not trusted, key is vulnerable.

• For example, a Trojan horse attack easily obtain the key.

FUTURE DIRECTION

• We plan to implement the Kerberos authentication protocol in more

smartcards, e.g. IBM

• Expect some differences in their performance because:

• Some of the smartcards have DES CBC mode.

• Some of the smartcards have key scheduling APIs.

• Communication speed difference among smart cards.

CONCLUSION

• We identified limitation of Kerberos that a smartcard can counter them.

• suggested a protocol takes advantage of secure features of smartcard to

enhance security of Kerberos.

• Protocol implemented with smartcard and KerberosV5-1.0.5.

• Performance evaluation shows the protocol runs fast.

BETTER ENCRYPTION

• The algorithms of cryptography driven by growth in computer power.

• Increasing computer power provides force for emerging cryptographic

algorithms:

• Solved older algorithms and short key lengths as they fall to brute-force

attacks.

• Makes possible complex calculations of algorithms and longer key.

• Kerberos depends heavily on cryptography.

• It is important new encryption methods implemented in the Kerberos protocol.

BETTER ENCRYPTION…

• Kerberos 5 protocol designed to support multiple encryption types.

• Internet drafts specify Stronger Encryption options for future

implementations of Kerberos protocols.

• AES is encryption algorithm used for future implementations for

Kerberos protocol.

• AES increasing the cryptographic security for future Kerberos

implementations.

WHO USES IT?

• Impossible to list all companies using Kerberos.

• Examples below relavent to the CyberSafe products.

• Kerberos is being used by 100 million people, worldwide.

• The following vendors implement Kerberos:

MICROSOFT

• Products which use Kerberos, are Microsoft Windows and Microsoft

Active Directory.

• In Microsoft network users authenticate using the Kerberos when logon

to Windows workstation.

• They only have to authenticate once when logon to workstation.

• The Microsoft XBOX also uses Kerberos protocol to authenticate users

to the Microsoft XBOX Live services on the Internet.

SAP

• Some of licensed software from SAP includes an implementation of

Kerberos.

• The protocol to control how it is used by their customers for licensing

reasons

• TrustBroker products can be used to implement security solutions, with

SAP business applications.

• Many customers chosing CyberSafe TrustBroker products for their SAP

business applications.

Q U E S T I O N S ?

T H A N K Y O U