Kerberos

• Akshat Sharma• Samarth Shah

OutlineWhat is Kerberos?

Why Kerberos?

Kerberos Model, Functionality, Benefits, Drawbacks

Sources of Information

Introduction

Importance

References

Functionality

About

How Kerberos works?

Conclusion Why it is important?

• Network authentication protocol.

• Developed at MIT in the mid 1980s.

• A secret key based service for providing authentication in open networks.

• Provides strong authentication for client-server applications.

What is Kerberos

• Authentication is a key feature in multi-user system.

• divide up resources with capabilities between many users.

• restrict user’s access to resources.• typical authentication mechanism –

passwords

Why Kerberos

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

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

• Firewalls make a risky assumption: that attackers are coming from the outside. In reality, attacks frequently come from within.

Why Kerberos

• Kerberos is based on the Secret-Key Distribution Model that was originally developed by Needham & Schroeder.

• keys are the basis of authentication in Kerberos.

• typically a short sequence of bytes.

• used to both encrypt & decrypt

Kerberos model

• Encryption => plaintext + Encryption key = ciphertext

• Decryption => ciphertext + Decryption key = plaintext

• Encryption Key – identical to – Decryption Key (in Conventional Crypto).

Kerberos model

• Three basic functions (message exchanges)• a request and a reply

1. The Authentication Service Exchange • (Logon)

2. The Ticket-Granting Service Exchange • (Getting a Ticket to Ride)

3. The Client/Server Authentication Exchange • (Accessing a Resource)

Kerberos Basics

• Authentication• Integrity – Is the assurance that the data received is

the same as generated.• Confidentiality – is the protection of info from

disclosure to those not intended to receive it.• Authorization – is the process by which one

determines whether a principal is allowed to perform an operation. Authorization is done usually after principal has been authenticated or based on authenticated statements by others.

Functions

• Instead of client sending password to application server:

• Request ticket from authentication server• Ticket and encrypted request sent to application

server

• Steps :• An user requests use of a network service

• Service wants assurance that user is who he says he is.

(Continued…….)

Kerberos Functionality

• User presents a ticket that is issued to it by a Kerberos Authentication Server(AS).

• If the ticket is valid, service is granted.

• The tickets must be unequivocally linked to the user

• Ticket demonstrates that the bearer knows something that only its intended user would know.

• Ticket must obviously be safeguarded against all attacks.

Kerberos Functionality

• More efficient authentication to servers. • Server can authenticate the client by examining

credentials. Clients can obtain credentials for a particular server once and reuse them throughout a network logon session.

• Mutual authentication. • Parties at both ends of a network connection can know

that the party on the other end is who it claims to be.

• Delegated authentication. • Kerberos protocol has a proxy mechanism that allows

a service to impersonate its client when connecting to other services.

Benefits of Kerberos

• Single point of failure: It requires continuous availability of a central server. When the Kerberos server is down, no one can log in.

• Kerberos has strict time requirements, which means the clocks of the involved hosts must be synchronized within configured limits.

• The administration protocol is not standardized and differs between server implementations.

• Since all authentication is controlled by a centralized KDC, compromise of this authentication infrastructure will allow an attacker to impersonate any user.

• Each network service which requires a different host name will need its own set of Kerberos keys. This complicates virtual hosting and clusters.

Drawbacks of Kerberos

• Authentication is critical for the security of computer systems. Without knowledge of the identity of a principal requesting an operation, it's difficult to decide whether the operation should be allowed.

• Traditional authentication methods are not suitable for use in computer networks where attackers monitor network traffic to intercept passwords.

• The use of strong authentication methods that do not disclose passwords is imperative. The Kerberos authentication system is well suited for authentication of users in such environments.

Conclusion

References

• Kerberos: An Authentication Service for Open Network Systems

• Steiner, Neuman, Schiller, 1988, Winter USENIX

• http://en.wikipedia.org/wiki/Kerberos_(protocol)

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