Akshat Sharma Samarth Shah Kerberos Akshat Sharma Samarth Shah

Outline What is Kerberos? Why Kerberos? How Kerberos works? Introduction What is Kerberos? Importance Why Kerberos? Functionality How Kerberos works? About Kerberos Model, Functionality, Benefits, Drawbacks Conclusion Why it is important? References Sources of Information

What is Kerberos 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.

Why 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.

Kerberos model 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 Basics Three basic functions (message exchanges) a request and a reply The Authentication Service Exchange (Logon) The Ticket-Granting Service Exchange (Getting a Ticket to Ride) The Client/Server Authentication Exchange (Accessing a Resource)

Functions 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.

Kerberos Functionality 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.

Benefits of Kerberos 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.

Drawbacks 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.

Conclusion 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.

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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