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Creating Keytab File for Kerberos Authentication in Active Directory

by | Mar 19, 2021

Creating a keytab file for Kerberos is quite easy. Take a peek at this blog for the steps.

The Kerberos protocol defines how clients interact with a network authentication service.

At Bobcares, we often receive requests relating to Kerberos queries as a part of our Server Management Services.

Today, let’s see the procedure of creating keytab file for Kerberos.

 

Creating a Keytab File for Kerberos Authentication in Active Directory

Linux services like Apache, Nginx, etc can use keytab files for Kerberos authentication in Active Directory without entering any password. The keytab file keeps the names of Kerberos principals and the corresponding encrypted keys. Now let’s take a look at how our Support Engineers create a keytab file.

First, we create a service account in AD and set a known password for it.

New-ADUser -Name "web" -GivenName "nginx web app" -SamAccountName "web" -UserPrincipalName "web@test.com" -Path "OU=Services,OU=Munich,OU=DE,DC=test,DC=com" –AccountPassword (ConvertTo-SecureString “Sup6r!Pa$s” -AsPlainText -force) -Enabled $true

Next, we enable “User cannot change password” and “Password never expires“ options for the service account in the graphic console or in PowerShell:

Get-ADUser web|Set-ADUser -PasswordNeverExpires:$True -CannotChangePassword:$true

Then, we bind a service principal name (SPN) to the user account. We need not perform this step separately since ktpass does it automatically when creating a keytab file (Here, we will do it so that you understand the process better).

Now, we bind the following SPN record to the web account:

setspn -A HTTP/www.test.com@test.com web

Then, we display the list of SPN records that associates with the AD user:

setspn -L web

To create a keytab file, we use the below command.

ktpass -princ HTTP/www.test.com@TEST.COM -mapuser web -crypto ALL -ptype KRB5_NT_PRINCIPAL -pass Sup6r!Pa$s -target mundc01.test.com -out c:\share\web.keytab

Now, the command creates a keytab file (c:\share\webt.keytab) for the SPN record of the HTTP/www@test.com service. The SPN record is bound to the web account with the specified password.

We make sure that the SPN record for the service has been successfully created (if you did not create it manually):

setspn -Q */www.test.com@test.com

Windows do not have built-in tools to view the contents of the keytab file. However, if Java JRE is present on the computer, we can use klist.exe included in the Java distribution package.

cd "c:\Program Files\Java\jre1.8.0_181\bin"
klist.exe -K -e -t -k c:\PS\web_host.keytab

 

Common Error

We had a customer with the below error message. He came across this error message while executing ktpass command to create a keytab file in Kerberos authentication using ktpass command for Kerberos.

Command: ktpass /princ HTTP/fqhostname@DOMAIN.COM /ptype krb5_nt_principal /crypto all /mapuser DOMAIN\serviceaccount /out bob.keytab -kvno 0 /pass password
Output:
Targeting domain controller: domaincontroller.Domain.com
Successfully mapped HTTP/fqhostname to serviceaccount
Password set failed! 0x00000035

The above error arises if the service account’s password does not meet the domain’s password policy.

Solution

In order to resolve this, we reset the account’s password by following the current domain’s password policy and re-run the ktpass command.

[Need any further assistance with Kerberos? – We’ll help you with it]

 

Conclusion

Today, we saw how our Support Engineers create keytab files for Kerberos.

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