Kerberos is a Network Protocol that uses Secret - key cryptography to authenticate client - server applications. It provides the difference between the Firewall and kerberos. And also this slides are gives the information about how does the Kerberos works in ticket granting service and in Application server. Kerberos are work Within networks and small sets of networks.

1. Bharathiar University
Department of Computer Applications
Kerberos
N.Mohanasundaram
II - MCA

2. Definition:
• Kerberos is a Network Protocol that
uses Secret - key cryptography to
authenticate client - server applications.
Kerberos requests an encrypted ticket
via an authenticated server sequence to
use services.

3. What is Kerberos?
• Network authentication
protocol
• Developed at MIT in the
mid 1980s
• Available as open
source or in supported
commercial software

4. 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.

5. 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.

6. 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.

7. Cryptography Approach
• Private Key: Each party uses the
same secret key to encode and
decode messages.
• Uses a trusted third party which
can vouch for the identity of both
parties in a transaction. Security of
third party is imperative.

8. 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)

9. How does Kerberos work?:
Ticket Granting Tickets

10. How does Kerberos Work?:
The Ticket Granting Service

11. How does Kerberos work?:
The Application Server

12. Applications
• Authentication
• Authorization
• Confidentiality
• Within networks and small
sets of networks

13. Weaknesses and
Solutions
I f TGT st olen, can be used
t o access net work
services.
Only a problem unt il
t icket expires in a
f ew hours.
Subj ect t o dict ionary
at t ack.
Timest amps require
hacker t o guess in 5
minut es.
Very bad if Aut hent icat ion
Server compromised.
Physical prot ect ion
f or t he server.

14. 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.

15. Limitation: Scalability
• Recent modifications attempt
to address this problem
• Public key cryptography for
Client Authentication and
cross realm authentication
• Issues are not resolved

16. Example:

17. Thank you