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)