Windows 2000 compatability
**************************

Windows 2000 (formerly known as Windows NT 5) from Microsoft implements Kerberos 5.  Their implementation, however, has some quirks, peculiarities, and bugs.  This chapter is a short summary of the things that we have found out while trying to test Heimdal against Windows 2000.  Another big problem with the Kerberos implementation in Windows 2000 is that the available documentation is more focused on getting things to work rather than how they work, and not that useful in figuring out how things really work.

This information should apply to Heimdal VERSION and Windows 2000 Professional.  It's of course subject to change all the time and mostly consists of our not so inspired guesses.  Hopefully it's still somewhat useful.

Configuring Windows 2000 to use a Heimdal KDC
=============================================

You need the command line program called ksetup.exe which is available in the file SUPPORT/TOOLS/SUPPORT.CAB on the Windows 2000 Professional CD-ROM. This program is used to configure the Kerberos settings on a Workstation.

Ksetup store the domain information under the registry key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\LSA\Kerberos\Domains.

Use the kadmin program in Heimdal to create a host principal in the Kerberos realm.

     unix% kadmin
     kadmin> ank --password=password host/datan.example.com

The name datan.example.com should be replaced with DNS name of the workstation.

You must configure the workstation as a member of a workgroup, as opposed to a member in an NT domain, and specify the KDC server of the realm as follows:

     C:> ksetup /setdomain EXAMPLE.COM
     C:> ksetup /addkdc EXAMPLE.COM kdc.example.com

Set the machine password, i.e. create the local keytab:

     C:> ksetup /SetComputerPassword password

The password used in ksetup /setmachpassword must be the same as the password used in the kadmin ank command.

The workstation must now be rebooted.

A mapping between local NT users and Kerberos principals must be specified. You have two choices. First:

     C:> ksetup /mapuser user@MY.REALM nt_user

This will map a user to a specific principal; this allows you to have other usernames in the realm than in your NT user database. (Don't ask me why on earth you would want that...)

You can also say:

     C:> ksetup /mapuser * *

The Windows machine will now map any user to the corresponding principal, for example nisse to the principal nisse@MY.REALM. (This is most likely what you want.)

Inter-Realm keys (trust) between Windows 2000 and a Heimdal KDC
===============================================================

See also the Step-by-Step guide from Microsoft, referenced below.

Install Windows 2000, and create a new controller (Active Directory Server) for the domain.

By default the trust will be non-transitive. This means that only users directly from the trusted domain may authenticate. This can be changed to transitive by using the netdom.exe tool. netdom.exe can also be used to add the trust between two realms.

You need to tell Windows 2000 on what hosts to find the KDCs for the non-Windows realm with ksetup, see Configuring Windows 2000 to use a Heimdal KDC.

This needs to be done on all computers that want enable cross-realm login with Mapped Names.

Then you need to add the inter-realm keys on the Windows KDC. Start the Domain Tree Management tool (found in Programs, Administrative tools, Active Directory Domains and Trusts).

Right click on Properties of your domain, select the Trust tab.  Press Add on the appropriate trust windows and enter domain name and password. When prompted if this is a non-Windows Kerberos realm, press OK.

Do not forget to add trusts in both directions (if that's what you want).

If you want to use netdom.exe instead of the Domain Tree Management tool, you do it like this:

     netdom trust NT.REALM.EXAMPLE.COM /Domain:EXAMPLE.COM /add /realm /passwordt:TrustPassword

You also need to add the inter-realm keys to the Heimdal KDC. Make sure you have matching encryption types (DES, Arcfour and AES in case of Longhorn)

Another issue is salting.  Since Windows 2000 does not seem to understand Kerberos 4 salted hashes you might need to turn off anything similar to the following if you have it, at least while adding the principals that are going to share keys with Windows 2000.

     [kadmin]
             default_keys = v5 v4

So remove v4 from default keys.

What you probably want to use is this:

     [kadmin]
             default_keys = des-cbc-crc:pw-salt arcfour-hmac-md5:pw-salt

Once that is also done, you can add the required inter-realm keys:

     kadmin add krbtgt/NT.REALM.EXAMPLE.COM@EXAMPLE.COM
     kadmin add krbtgt/REALM.EXAMPLE.COM@NT.EXAMPLE.COM

Use the same passwords for both keys.

Do not forget to reboot before trying the new realm-trust (after running ksetup). It looks like it might work, but packets are never sent to the non-Windows KDC.

Create account mappings
=======================

Start the Active Directory Users and Computers tool. Select the View menu, that is in the left corner just below the real menu (or press Alt-V), and select Advanced Features. Right click on the user that you are going to do a name mapping for and choose Name mapping.

Click on the Kerberos Names tab and add a new principal from the non-Windows domain.

This adds authorizationNames entry to the users LDAP entry to the Active Directory LDAP catalog. When you create users by script you can add this entry instead.

Encryption types
================

Windows 2000 supports both the standard DES encryptions (des-cbc-crc and des-cbc-md5) and its own proprietary encryption that is based on MD4 and RC4 that is documented in and is supposed to be described in draft-brezak-win2k-krb-rc4-hmac-03.txt.  New users will get both MD4 and DES keys.  Users that are converted from a NT4 database, will only have MD4 passwords and will need a password change to get a DES key.

Authorisation data
==================

The Windows 2000 KDC also adds extra authorisation data in tickets. It is at this point unclear what triggers it to do this.  The format of this data is only available under a ``secret'' license from Microsoft, which prohibits you implementing it.

A simple way of getting hold of the data to be able to understand it better is described here.

 1. Find the client example on using the SSPI in the SDK documentation.

 2. Change ``AuthSamp'' in the source code to lowercase.

 3. Build the program.

 4. Add the ``authsamp'' principal with a known password to the database.  Make sure it has a DES key.

 5. Run ktutil add to add the key for that principal to a keytab.

 6. Run appl/test/nt_gss_server -p 2000 -s authsamp --dump-auth=FILE where FILE is an appropriate file.

 7. It should authenticate and dump for you the authorisation data in the file.

 8. The tool lib/asn1/asn1_print is somewhat useful for analysing the data.

Quirks of Windows 2000 KDC
==========================

There are some issues with salts and Windows 2000.  Using an empty salt---which is the only one that Kerberos 4 supported, and is therefore known as a Kerberos 4 compatible salt---does not work, as far as we can tell from out experiments and users' reports.  Therefore, you have to make sure you keep around keys with all the different types of salts that are required.  Microsoft have fixed this issue post Windows 2003.

Microsoft seems also to have forgotten to implement the checksum algorithms rsa-md4-des and rsa-md5-des. This can make Name mapping (see Create account mappings) fail if a des-cbc-md5 key is used. To make the KDC return only des-cbc-crc you must delete the des-cbc-md5 key from the kdc using the kadmin del_enctype command.

     kadmin del_enctype lha des-cbc-md5

You should also add the following entries to the krb5.conf file:

     [libdefaults]
     	default_etypes = des-cbc-crc
     	default_etypes_des = des-cbc-crc

These configuration options will make sure that no checksums of the unsupported types are generated.

Useful links when reading about the Windows 2000
================================================

See also our paper presented at the 2001 Usenix Annual Technical Conference, available in the proceedings or at http://www.usenix.org/publications/library/proceedings/usenix01/freenix01/westerlund.html.

There are lots of texts about Kerberos on Microsoft's web site, here is a short list of the interesting documents that we have managed to find.

  * Step-by-Step Guide to Kerberos 5 (krb5 1.0) Interoperability: http://www.microsoft.com/technet/prodtechnol/windows2000serv/howto/kerbstep.mspx. Kerberos GSS-API (in Windows-eze SSPI), Windows as a client in a non-Windows KDC realm, adding unix clients to a Windows 2000 KDC, and adding cross-realm trust (see Inter-Realm keys (trust) between Windows 2000 and a Heimdal KDC).

  * Windows 2000 Kerberos Authentication: www.microsoft.com/technet/prodtechnol/windows2000serv/deploy/confeat/kerberos.mspx. White paper that describes how Kerberos is used in Windows 2000.

  * Overview of Kerberos: http://support.microsoft.com/support/kb/articles/Q248/7/58.ASP. Links to useful other links.

  * Event logging for Kerberos: http://support.microsoft.com/support/kb/articles/Q262/1/77.ASP. Basically it say that you can add a registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters\LogLevel with value DWORD equal to 1, and then you'll get logging in the Event Logger.

Other useful programs include these:

  * pwdump2 http://www.bindview.com/Support/RAZOR/Utilities/Windows/pwdump2_readme.cfm itemize