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I was provided a headless Active Directory user account with a randomly generated password we need to use to access some network resources. Since this headless account will need to be run from an automated job, I'm trying to create a keytab file that can be used with kinit. Since this is a user account, not a service account, and I don't have admin access for AD, I can't use kadmin to create it. Instead, I'm trying to use ktutil to generate the correct keytab file and store it in a secure location. As I understand it, the keytab file just contains the raw encryption keys as produced by a standard string2key Kerberos function based on the user's password and salt. The salt comes from the server in the preauth, but it normally just the username and realm.

I can manually acquire a Kerberos ticket for the user:

kinit headless@REALM

Running klist -e, I see it's using the encryption type aes256-cts-hmac-sha1-96 for the service key and TGT. The kvno is a bit trickier to get, but from Wireshark, I found it's value. Using ktutil, I create the keytab:

# ktutil
add_entry -password -p headless@REALM -k 3 -e aes256-cts-hmac-sha1-96
write_kt headless.keytab
quit

To use the keytab file, I'm running this:

kinit headless@REALM -k -t headless.keytab

However, I get a preauth error trying to get the TGT. From a little research, it sounds like the salt used in Microsoft AD might not be conventional so I tried extracting the salt from Wireshark by carefully examining the salt field from the PA-ETYPE-INFO2 preauth data in the Kerberos server response. Indeed, it included the username and realm, but adding the salt to the ktutil add_entry -s option and it still did not accept it.

What is the correct procedure to create a keytab file on Linux for a headless AD account?

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