Kerberos is a network authentication protocol that uses tickets to authenticate users and services in a Windows Active Directory environment. In this section, we will explain the function of Active Directory Kerberos tickets, the authentication flow, and usage examples.
Function: Active Directory Kerberos tickets are used to authenticate users and services in a Windows Active Directory environment. When a user logs on to a computer and attempts to access a network resource, the computer sends a request to the domain controller for a Kerberos ticket. The domain controller validates the user’s credentials and issues a Kerberos ticket, which is used to access the network resource.
Authentication Flow: The following steps explain the authentication flow of Active Directory Kerberos tickets:
- User Authentication: The user logs on to their computer with their username and password.
- Request for a Ticket-Granting Ticket (TGT): The user’s computer requests a TGT from the domain controller. The TGT is used to request a service ticket for a specific service.
- TGT Issuance: The domain controller validates the user’s credentials and issues a TGT. The TGT contains the user’s identity and a timestamp.
- Service Ticket Request: The user’s computer sends a service ticket request to the domain controller for the network resource they want to access.
- Service Ticket Issuance: The domain controller validates the user’s TGT and issues a service ticket. The service ticket contains the user’s identity, the service they want to access, and a timestamp.
- Service Ticket Presentation: The user’s computer presents the service ticket to the network resource they want to access. The network resource validates the ticket and grants access to the user.
Usage Examples: Here are some examples of how Active Directory Kerberos tickets are used in Windows Active Directory environments:
- Single Sign-On (SSO): Kerberos tickets enable SSO, which allows users to log on once and access multiple network resources without having to log on to each resource separately.
- Secure Authentication: Kerberos tickets provide secure authentication because the tickets are encrypted and the authentication process involves multiple steps, which makes it difficult for attackers to intercept and exploit.
- Domain Join: When a computer joins a domain, it receives a machine account and a TGT that is used to authenticate the computer to the domain controller and other network resources.
- Smart Card Authentication: Kerberos tickets can be used with smart cards to provide two-factor authentication, which requires something the user has (smart card) and something the user knows (PIN).
Active Directory krbtgt
In Active Directory, krbtgt is a built-in account that is used by the Key Distribution Center (KDC) to encrypt and sign Kerberos tickets. The krbtgt account is automatically created when the Active Directory domain is created, and it is used for all Kerberos authentication in the domain.
The krbtgt account is used to generate a master key, which is used to encrypt and sign all Kerberos tickets issued by the KDC. Each domain in Active Directory has its own krbtgt account, and the account’s password is changed automatically every 30 days. The password change is an important security feature, as it ensures that any compromised tickets issued with the old password become invalid after the password is changed.
The krbtgt account is also protected by an Access Control List (ACL), which restricts access to the account. Only the KDC and domain administrators have access to the krbtgt account. This is important because compromising the krbtgt account could allow an attacker to generate fake Kerberos tickets, which could be used to gain unauthorized access to resources on the network.
The krbtgt account is a critical component of the Active Directory Kerberos authentication system. It is used to generate the master key for encrypting and signing Kerberos tickets, and it is protected by an ACL to prevent unauthorized access. The automatic password change feature ensures that any compromised tickets become invalid after the password is changed.
