July 28, 2022

Kerberos Explained

Cybercrime is an unfortunate fact these days; no company or organization is safe, regardless of talking about private or business at large. The problem won’t improve these days unless we can use our protocol with an effective network solution.

Experts have predicted that cybercrime will damage the cost of the world by $25trillion by the end of 2025; strange, isn’t it?

Another prediction by Forbes says that the constant use of mobile devices is increasing the rate of cybercrimes, and there is no stopping it. Consequently, the digital world is logging in to find new strategies to strengthen cyber security. These predictions are so many that you are not ready to listen to or even process in your mind.

Today, we are looking for a Kerberos authentication network protocol. Let’s pull back the curtains and know what is Kerberos?

What is Kerberos? 

The Internet is an insecure place. Some systems deploy firewalls to prevent unauthorized access to computers. But firewalls assume bad guys are outside, and that is a problem. The majority of malicious attempts are done from the inside.

Using strong cryptography, Kerberos is a protocol for authenticating network service requests between trusted hosts across an untrusted network. It uses security key cryptography and a trusted third party for establishing client-server applications and verifying users’ identities.

Kerberos is an authentication protocol based on a ticketing mechanism in which a client authenticates itself to an Authentication Server (AS) and receives a ticket (various steps involved in between communication with a Key Distribution Centre) which it can reuse with all nodes using the same KDC. So, in an internal network, you can access nodes by authenticating yourself to an AS and then reusing the ticket to access other nodes.

Where is Kerberos protocol mainly used? 

Kerberos is used mainly on secure systems which require reliable auditing and authentication features. It’s used in Posix authentication, an alternative authentication system for ssh, POP, and SMTP, in Active Directory, NFS, Samba, and quite a few other similar projects. It can regularly be used as a drop-in system for anything that understands POSIX authentication, which is quite a bit.

The original OpenAuth project used a similar system, with tokens replacing the ticket concept from the client’s standpoint. Know at least a few other implementations that used Kerberos style authentication and auditing for web service communication layers in cloud systems.

It’s a great system, though because of POSIX, you’ll be able to find the authorization a little draconian, but like most things, you can “roll your own,” and the rest of the application will respect just the way you want it. It also helps that authorization should be done regularly, whereas authentication only occurs with new connections when a previous ticket expires or after a connection loss or termination.

What are the benefits of Kerberos authentication? 

Kerberos brings a ton of advantages to any cybersecurity setup. The main benefits are:

  • Effective access control: Kerberos gives users one point to keep track of securities and logins policy enforcement.
  • Secured lifetime access for critical tickets: Each Kerberos ticket has a ticket timestamp, lifetime data, and authentication timeline controlled by the administrator.
  • On-point authentication: Some service systems and users can authenticate and use each other through mutual authentication.
  • Reusable authentication: whoever uses Kerberos authentication can reuse and are durable, requiring each user to get verified by the system just once. As far as the ticket is usable, the user won’t have to keep their details for authentication purposes.
  • Solid and diverse security measures: Kerberos has security authentication protection to employ cryptography, several secret keys, and third-party authorization, creating a reliable and secure defense. One thing about Kerberos is that passwords do not send over networks, whereas private keys are encrypted.

What is the Kerberos protocol flow overview? 

Here is a more detailed version of what Kerberos authentication is all about. Also, know how it works by breaking it down into different steps and its core components.

Here are the principal entities engrossed in the Kerberos protocol flow.

  • Client: The client acts in the name of the user experience and serves as communication for a service request.
  • Server: The server hosts the user who wants to access it.
  • An authentication server (AS): The AS performs the required client authentication. If the authentication is launched successfully, the client receives a ticket called TGT (ticket-granting ticket), basically a confirmation that the other clients’ servers are authenticated.
  • Key Distribution Center (KDC): In a Kerberos atmosphere, the authentication is logically separated into three different parts
  • A database 
  • An authentication server (AS)
  • Ticket granting ticket (TGT)

These three parts run, turn and exist in a single server called the Key Distribution Center (KDC).

The protocol flow consists of the following steps: 

Step 1: Initially, the client authentication request goes. The user asks for a TGT from the authentication server (AS), which includes the client ID for proof.

Step 2: KDC verifies the above process with the client’s credentials. The AS checks the data for the client’s security and finds both the values; it issues a secret client key, employing the password with harsh words.

Step 3: The client passes on the message. The client or the user uses the secret key decrypt to message and generates the SK1 and TGT of the authentication that validates the client’s ticket.

Step 4: The client uses ticketing to access the request generated. The clients require a ticket from the server offering the service by sending the key and creating the authentication to TGS.

Step 5: KDC generates a ticket for the file server. The TGT then uses the TGS secret key to describe the TGT received from the user to extract SK1. The TGS checks if the data matches the client ID and address.

Finally, the KDC creates a service ticket containing the client ID, address, timestamp, and SK2.

Step 6: The client uses the file server ticket to authenticate Sk1 and Sk2.

Step 7: The targeted server then receives the decryption and authentication. The target person uses the server’s secret key to decrypt the ticket issued and extract SK2.

Once the checks are met, the targeted server sends the client message verifying the client and the AS each other. The user is now ready to engage in a secure session.


At the end of the article, we hope you got a descriptive overview of what Kerberos is. For more learning about Kerberos, Simplilearn offers Simplilearn online learning for all aspirants willing to learn Kerberos.

About the author 

Peter Hatch

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