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In Security Last updated: October 12, 2022
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Although Kerberos is a back-end system, it is so seamlessly integrated that most users or administrators overlook its existence.

What is Kerberos, and how does it work? 

If you use email or other online services that require logins to access resources, the chances are that you are authenticating through the Kerberos system.

The secure authentication mechanism known as Kerberos guarantees safe communication between devices, systems, and networks. Its main objective is to safeguard your data and login information from hackers.


Kerberos is supported by all popular operating systems, including Microsoft Windows, Apple macOS, FreeBSD, and Linux.

 A five-level security model used by Kerberos comprises mutual authentication and symmetric key cryptography. Verifying one’s identity enables authorized users to log into a system.

It combines a central database and encryption to confirm the legitimacy of users and services. The Kerberos server first authenticates a user before allowing them access to a service. They are then issued a ticket they can use to access the service if they are successfully authenticated.

In essence, Kerberos relies on “tickets” to allow users to communicate with one another securely. Kerberos protocol uses a Key Distribution Center (KDC) to establish communication between clients and servers.

When using the Kerberos protocol, the server receives a request from the client. After that, the server replies with a response that contains a token. The client then issues a request to the server and the ticket.

It is an essential method that guarantees the safety of data transferred across systems. It was developed by the Massachusetts Institute of Technology (MIT) in 1980 to address the issue of unsecured network connections and is now included in many different systems.

In this article, we’ll look at specifics on Kerberos advantages, practical applications, how it operates step-by-step, and how safe it is.

Benefits of Kerberos Authentication

In a vast, distributed computing environment, computer systems can safely identify and communicate with one another due to the network authentication protocol known as Kerberos.

Using secret-key cryptography, Kerberos is intended to offer robust authentication for client/server applications. This protocol lays the groundwork for application security, and SSL/TLS encryption is frequently used in combination with it.

The widely used authentication protocol Kerberos offers several advantages that may make it more appealing to SMBs and large corporations.

In the first place, Kerberos is incredibly trustworthy; it has been tested against some of the most complex attacks and has proven immune to them. Furthermore, Kerberos is simple to set up, utilize, and integrate into several systems.

Unique benefits

  • A unique ticketing system used by Kerberos enables quicker authentication.
  • Services and clients can mutually authenticate each other.
  • The authentication period is particularly secure because of the limited time stamp.
  • Meets the requirements of modern distributed systems
  • Reusable while the ticket timestamp is still valid, Authenticity prevents users from having to re-enter their login information to access other resources.
  • Multiple secret keys, third-party authorization, and cryptography provide top-notch security.

How safe is Kerberos?

We’ve seen that Kerberos employs a secure authentication process. This section will explore how attackers may violate Kerberos security. 


For many years, the Kerberos secure protocol has been in use: As an illustration, since the release of Windows 2000, Microsoft Windows has made Kerberos the standard authentication mechanism.

The Kerberos authentication service uses secret-key encryption, cryptography, and trusted third-party authentication to protect sensitive data successfully while in transit.

To increase security, Advanced Encryption Standard (AES) is used by Kerberos 5, the most recent version, to ensure more secure communications and avoid data intrusions.

The US government has adopted AES because it is particularly effective at protecting its secret information.

However, it is argued that no platform is entirely safe, and Kerberos is no exception. Even though Kerberos is the most secure, businesses must constantly check their attack surface to guard against being taken advantage of by hackers.

As a result of its broad use, hackers strive to uncover security gaps in the infrastructure.

Here are a few typical attacks that may occur:

  • Golden Ticket attack: It is the most damaging assault. In this assault, attackers hijack a genuine user’s key distribution service using Kerberos tickets. It primarily targets Windows environments with Active Directory (AD) in use for access control privileges.
  • Silver Ticket Attack: A faked service authentication ticket is referred to as a silver ticket. A hacker can produce a Silver Ticket by deciphering a computer account password and utilizing it to construct a false authentication ticket.
  • Pass the ticket: By generating a false TGT, the attacker constructs a fake session key and presents it as a legitimate credential.
  • Pass the hash attack: This tactic entails obtaining the NTLM password hash of a user and then transmitting the hash for NTLM authentication.
  • Kerberoasting: The attack aims to gather password hashes for Active Directory user accounts with servicePrincipalName (SPN) values, such as service accounts, by abusing the Kerberos protocol.

Kerberos Risks Mitigation

The following mitigating measures would aid in preventing the Kerberos attacks:

  • Adopt modern software that monitors the network around the clock and identifies vulnerabilities in real-time.
  • Least Privilege: It states that only those users, accounts, and computer processes should have access permissions necessary for them to do their jobs. By doing this, unauthorized access to servers, mainly KDC Server and other domain controllers, will be stopped.
  • Overcome Software Vulnerabilities, including zero-day vulnerabilities.
  • Run the protected mode of the Local Security Authority Subsystem Service (LSASS): LSASS hosts various plugins, including NTLM authentication and Kerberos, and is in charge of providing users with single sign-on services.
  • Strong Authentication: Standards for password creation. Strong passwords for administrative, local, and service accounts.
  • DOS (Denial of service) attacks: By overloading the KDC with authentication requests, an attacker can launch a denial-of-service (DoS) attack. To prevent assaults and balance the load, KDC should be placed behind a firewall, and additional redundant KDC redundant should be deployed.

What are the steps in the Kerberos Protocol Flow?

The Kerberos architecture primarily consists of four essential elements that handle all Kerberos operations:

  • Authentication Server (AS): The Kerberos authentication process begins with the Authentication Server. The client must first log in to the AS using a username and password to establish their identity. When this is finished, the AS sends the username to the KDC, which then issues a TGT.
  • Key Distribution Center (KDC): Its job is to serve as a liaison between the Authentication Server (AS) and the Ticket Granting Service (TGS), relaying messages from the AS and issuing TGTs, which are subsequently passed to the TGS for encryption.
  • Ticket-Granting Ticket (TGT): TGT is encrypted and contains information on which services the client is allowed to access, how long that access is authorized, and a session key for communication.
  • Ticket Granting Service (TGS): TGS is a barrier between clients who own TGTs and the network’s various services. The TGS then establishes a session key after authenticating the TGT shared by the server and client.

The following is the stepwise flow of the Kerberos Authentication:

  • User login
  • A client requests the server that grants tickets.
  • A server checks the username.
  • Returning the client’s ticket after the grant.
  • A client obtains the TGS session key.
  • A client asks the server for access to a service.
  • A server checks the service.
  • TGS Session Key obtained by the server.
  • A server creates Service Session Key.
  • A client receives the service session key.
  • A client contacts the service.
  • Service Decrypts.
  • Service checks the request.
  • Service is authenticated to the client.
  • A client confirms the service.
  • A client and service interact.

What are real-world applications using Kerberos?

In a modern internet-based and connected workplace, Kerberos is significantly more valuable because it is excellent at Single-Sign-On (SSO).

Microsoft Windows presently uses Kerberos authentication as its standard authorization method. Kerberos is also supported by Apple OS, FreeBSD, UNIX, and Linux.


Additionally, it has become a norm for websites and Single-Sign-On applications across all platforms. Kerberos has increased the security of the internet and its users while allowing users to perform more tasks online and in the office without risking their safety.

Popular operating systems and software programs already include Kerberos, which has become an essential part of IT infrastructure. It is Microsoft Windows’ standard authorization technology.

It uses strong cryptography and third-party ticket authorization to make it more difficult for hackers to access a corporate network. Organizations can use the internet with Kerberos without worrying about jeopardizing their security.

The most well-known application of Kerberos is Microsoft Active Directory, which controls domains and performs user authentication as a standard directory service included in Windows 2000 and later.

Apple, NASA, Google, the US Department of Defense, and institutions throughout the country are among the more notable users.

Below are some examples of systems with built-in or accessible Kerberos support:

  • Amazon Web Services
  • Google Cloud
  • Hewlett Packard Unix
  • IBM Advanced Interactive executive
  • Microsoft Azure
  • Microsoft Windows Server and AD
  • Oracle Solaris
  • OpenBSD

Additional Resources

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The most widely used authentication method for protecting client-server connections is Kerberos. Kerberos is a symmetric key authentication mechanism that offers data integrity, confidentiality, and mutual user authentication.

It is the foundation of Microsoft Active Directory and has grown to be one of the protocols that attackers of all kinds target for exploitation.

Next, you can check out tools to monitor the health of Active Directory.

  • Satish Shethi
    I have been in the IT industry for more than 20 years. I have served Fortune 100 company in a senior role looking after projects related to US Banking, BFS, Mortgage, Insurance, and FMCG. Apart from IT, I like to read books, especially spirituality… read more
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