Description of password-change protocols in Windows 2000 (264480)

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Windows 2000 supports many protocols for changing passwords, but they are used under different circumstances. The supported password-change protocols are:

1. The NetUserChangePassword protocol
2. The NetUserSetInfo protocol
3. The Kerberos change-password protocol (IETF Internet Draft Draft-ietf-cat-kerb-chg-password-02.txt) [port 464]
4. Kerberos set-password protocol (IETF Internet Draft Draft-ietf-cat-kerberos-set-passwd-00.txt) [port 464]
5. Lightweight Directory Access Protocol (LDAP) write-password attribute (if 128-bit Secure Sockets Layer [SSL] is used)
6. XACT-SMB for pre-Microsoft Windows NT (LAN Manager) compatibility

Change-password operations require that the user's current password be known before the change is allowed. Set-password operations do not have this requirement, but are controlled by the Reset Password right on the account.

When you are using LDAP (method 5), the domain controller and the client must both be able to use 128-bit SSL to protect the connection. If the domain controller is not configured for SSL or if appropriately long keys are not available, the password-change write is denied.

A Windows 2000-based domain controller listens for change-password requests on all of these protocols.

As stated earlier in this article, different protocols are used in different circumstances. For example:

• Interoperable Kerberos clients use the Kerberos protocols. UNIX-based systems with MIT Kerberos version 5 1.1.1 can change user passwords in a Windows 2000-based domain by using the Kerberos change-password protocol (method 3).
  
  A sample implementation is available at the following Microsoft Web site:

  http://msdn.microsoft.com/library/techart/kerberossamp.htm

  .
• When a user changes his or her own password by pressing CTRL+ALT+DELETE and then clicking Change Password, the NetUserChangePassword mechanism (method 1) is used if the target is a domain. If the target is a Kerberos realm, the Kerberos change-password protocol (method 3) is used.
• Requests to change a password from computers that are running Microsoft Windows NT 3.x or 4.0 use the NetUserChangePassword and NetUserSetInfo protocols (methods 1 and 2).
• Requests to change a password from computers that are running Microsoft Windows 95/Microsoft Windows 98 use XACT-SMB (method 6 ).
• A program that uses the ChangePassword method on the Active Directory Services Interface (ADSI) IaDSUser interface first tries to change the password by using LDAP (method 5), and then by using the NetUserChangePassword protocol (method 1).
• A program that uses the SetPassword method on the ADSI IaDSUser interface first tries to change the password by using LDAP (method 5), then the Kerberos set-password protocol (method 4), and then the NetUserSetInfo protocol (method 2).
• The Active Directory Users and Computers snap-in uses ADSI operations for setting user passwords.