Create a Kerberos service principal and keytab file


This task is necessary to process SPNEGO Web or Kerberos authentication requests to WAS. We can create a Kerberos service principal and keytab name using Microsoft Windows, iSeries, Linux, Solaris, Massachusetts Institute of Technology (MIT) and z/OS KDCs.

Create a Kerberos service principal and keytab using Microsoft Windows KDC:

This task is performed on the active directory domain controller machine. Complete the following steps to verify the Microsoft Windows 2000 or Windows 2003 Server that is running the active directory domain controller is configured properly to the associated key distribution center (KDC).

  1. Create a user account in the Microsoft Active Directory for the WAS.

    Click Start->Programs->Administrative Tools->Active Directory Users and Computers.

    Use the name for the WAS. For example, if the appserver we are running on the WAS machine is called myappserver.mpls.setgetweb.com, create a new user in an Active Directory called myappserver. Make sure that you do not have the computer name myappserver under Computers and Domain Controllers. If we already have a computer named myappserver, then create a different user account name.

    • Click Start -> Programs -> Administrative Tools -> Active Directory Users and Computers->Computers.

    • Click Programs -> Administrative Tools -> Active Directory Users and Computers->Domain Controllers.

  2. Use the setspn command to map the Kerberos service principal name, <service name>/<fully qualified host name>, to a Microsoft user account.

    The service name for SPNEGO Web authentication must be HTTP. However, the service name for Kerberos authentication can be any strings that are allowed by the KDC.

    An example of the setspn command usage for SPNEGO Web authentication is as follows:

    C:\Program Files\Support Tools> setspn -A HTTP/myappserver.mpls.setgetweb.com myappserver
    
    

    The host name must be a fully-qualified host name.

    Make sure that you do not have the same service principle names (SPNs) mapping to more than one Microsoft user account. If we map the same SPN to more than one user account, the web browser client can send an NT LAN manager (NTLM) token instead of a SPNEGO token to WAS.

  3. Create the Kerberos keytab file and make it available to WAS. Use the ktpass tool from the Windows Server toolkit to create the Kerberos keytab file (krb5.keytab) for the service principal name (SPN).

    A Kerberos keytab file contains a list of keys that are analogous to user passwords. It is important for hosts to protect their Kerberos keytab files by storing them on the local disk.

    Use the ktpass tool from the Windows Server toolkit to create the Kerberos keytab file for the service principal name (SPN). Use the latest version of the ktpass tool that matches the Windows server level that we are using. For example, use the Windows 2000 version of the tool for a Windows 2000 Server, or a Windows 2003 version of the tool for a Windows 2003 server.

    To determine the appropriate parameter values for the ktpass tool, run the ktpass -? command from the command line. This command lists whether the ktpass tool, which corresponds to the particular operating system, uses the -crypto RC4-HMAC or -crypto RC4-HMAC-NT parameter value. To avoid warning messages from the toolkit, specify the -ptype KRB5_NT_PRINCIPAL parameter value.

    The Windows 2003 server version of the ktpass tool supports the encryption type, RC4-HMAC, and Single data encryption standard (DES). The Windows 2000 server version of the ktpass tool are similar, but different options are necessary for the RC4-HMAC encryption type and single DES.

    See about the ktpass tool, see Windows 2003 Technical Reference (Kerberos keytab file and ktpass command) or Use Ktpass.exe in Windows 2000.

    The following code shows the functions that are available when you enter ktpass -? command on the command line. This information might be different depending on the version of the toolkit that we are using.

    C:\Program Files\Support Tools>ktpass -?                                   Command line options:                                                     
                                                                              
    ---------------------most useful args                                     
    [- /]          out : Keytab to produce                                    
    [- /]        princ : Principal name (user@REALM)                          
    [- /]         pass : password to use                                      
                         use "*" to prompt for password.                      
    [- +]      rndPass : ... or use +rndPass to generate a random password    
    [- /]      minPass : minimum length for random password (def:15)          
    [- /]      maxPass : maximum length for random password (def:256)         
    ---------------------less useful stuff                                    
    [- /]      mapuser : map princ (above) to this user account (default:      don't)                                                                    
    [- /]        mapOp : how to set the mapping attribute (default: add it)   
    [- /]        mapOp :  is one of:                                          
    [- /]        mapOp :        add : add value (default)                     
    [- /]        mapOp :        set : set value                               
    [- +]      DesOnly : Set account for des-only encryption (default:don't)  
    [- /]           in : Keytab to read/digest                                
    ---------------------options for key generation                           
    [- /]       crypto : Cryptosystem to use                                  
    [- /]       crypto :  is one of:                                          
    [- /]       crypto : DES-CBC-CRC : for compatibility                      
    [- /]       crypto : DES-CBC-MD5 : for compatibliity                      
    [- /]       crypto : RC4-HMAC-NT : default 128-bit encryption             
    [- /]        ptype : principal type in question                           
    [- /]        ptype :  is one of:                                          
    [- /]        ptype : KRB5_NT_PRINCIPAL : The general ptype-- recommended  
    [- /]        ptype : KRB5_NT_SRV_INST : user service instance             
    [- /]        ptype : KRB5_NT_SRV_HST : host service instance              
    [- /]         kvno : Override Key VNumber                          
                         Default: query DC for kvno.  Use /kvno 1 for Win2K    compat.                                                                   
    [- +]       Answer : +Answer answers YES to prompts.  -Answer answers      NO.                                                                       
    [- /]       Target : Which DC to use.  Default:detect                     
    ---------------------options for trust attributes (Windows Server 2003     Sp1 Only                                                                  
    [- /] MitRealmName : MIT Realm which we want to enable RC4 trust on.      
    [- /]  TrustEncryp : Trust Encryption to use; DES is default              
    [- /]  TrustEncryp :  is one of:                                          
    [- /]  TrustEncryp :        RC4 : RC4 Realm Trusts (default)              
    [- /]  TrustEncryp :        DES : go back to DES
    

    Do not use the -pass switch on the ktpass command to reset a password for a Microsoft Windows server account. See Windows 2003 Technical Reference (Kerberos keytab file and ktpass command) for more information.Depending on the encryption type, you use the ktpass tool in one of the following ways to create the Kerberos keytab file.

    The following section shows the different types of encryption that are used by the ktpass tool. It is important that you run the ktpass -? command to determine which -crypto parameter value is expected by the particular toolkit in the Microsoft Windows environment.

    • For a single DES encryption typeFrom a command prompt, run the ktpass command:

      ktpass -out c:\temp\myappserver.keytab
      -princ HTTP/myappserver.mpls.setgetweb.com@WSSEC.AUSTIN.IBM.COM
      -mapUser myappserv 
      -mapOp set 
      -pass was1edu
      -crypto DES-CBC-MD5 
      -pType KRB5_NT_PRINCIPAL
      +DesOnly
      


      Table 1. Using ktpass for a single DES encryption type

      Option Explanation
      -out c:\temp\myappserver.keytab The key is written to this output file.
      -princ HTTP/myappserver.mpls.setgetweb.com@WSSEC.AUSTIN.IBM.COM The concatenation of the user logon name, and the realm must be in uppercase.
      -mapUser The key is mapped to the user, myappserver.
      -mapOp This option sets the mapping.
      -pass was1edu This option is the password for the user ID.
      -crypto DES-CBC-MD5 This option uses the single DES encryption type.
      -pType KRB5_NT_PRINCIPAL This option specifies the KRB5_NT_PRINCIPAL principal value. Specify this option to avoid toolkit warning messages.
      +DesOnly This option generates only DES encryptions.

    • For the RC4-HMAC encryption type

      RC4-HMAC encryption is only supported when using a Windows 2003 Server as KDC. RC4-HMAC encryption is not supported with a Windows 2000 Server as KDC. From a command prompt, run the ktpass command.

      ktpass -out c:\temp\myappserver.keytab 
      -princ HTTP/myappserver.mpls.setgetweb.com@WSSEC.AUSTIN.IBM.COM 
      -mapUser myappserver
      -mapOp set 
      –pass was1edu 
      -crypto RC4-HMAC
      -pType KRB5_NT_PRINCIPAL
      


      Table 2. Using ktpass for the RC4-HMAC encryption type

      Option Explanation
      -out c:\temp\myappserver.keytab The key is written to this output file.
      -princ HTTP/myappserver.mpls.setgetweb.com@WSSEC.AUSTIN.IBM.COM The concatenation of the user logon name, and the realm must be in uppercase.
      -mapUser The key is mapped to the user, myappserver.
      -mapOp This option sets the mapping.
      -pass was1edu This option is the password for the user ID.
      -crypto RC4-HMAC This option chooses the RC4-HMAC encryption type.
      -pType KRB5_NT_PRINCIPAL This option specifies the KRB5_NT_PRINCIPAL principal value. Specify this option to avoid toolkit warning messages.

    • For the RC4-HMAC-NT encryption typeFrom a command prompt, run the ktpass command.

      ktpass -out c:\temp\myappserver.keytab 
      -princ HTTP/myappserver.mpls.setgetweb.com@WSSEC.AUSTIN.IBM.COM 
      -mapUser myappserver 
      -mapOp set 
      -pass was1edu 
      -crypto RC4-HMAC-NT
      -pType KRB5_NT_PRINCIPAL
      


      Table 3. Using ktpass for the RC4-HMAC encryption type

      Option Explanation
      -out c:\temp\myappserver.keytab The key is written to this output file.
      -princ HTTP/myappserver.mpls.setgetweb.com@WSSEC.AUSTIN.IBM.COM The concatenation of the user logon name, and the realm must be in uppercase.
      -mapUser The key is mapped to the user, myappserver.
      -mapOp This option sets the mapping.
      -pass was1edu This option is the password for the user ID.
      -crypto RC4-HMAC-NT This option chooses the RC4-HMAC-NT encryption type.
      -pType KRB5_NT_PRINCIPAL This option specifies the KRB5_NT_PRINCIPAL principal value. Specify this option to avoid toolkit warning messages.

      The Kerberos keytab file is created for use with the SPNEGO TAI.

Create a Kerberos service principal and keytab file using iSeries, Linux, Solaris and MIT KDCs:

See the Kerberos implementation documents for the kadmin, kadmin.local addprinc and ktadd commands for more detailed information.

This task is performed on a Linux, Solaris or MIT KDC machine.

  1. Create a Kerberos service principal for Kerberos authentication. For example:

    WAS/testmach.mpls.setgetweb.com  kadmin.local: addprinc WAS/testmach.mpls.setgetweb.com 
    

  2. Add the newly-created Kerberos service principal, WAS/testmach.mpls.setgetweb.com to a default krb5.keytab file. For example:

    kadmin.local: ktadd WAS/testmach.mpls.setgetweb.com 
    

Create a Kerberos service principal and keytab file using z/OS KDC:

Before SPNEGO Web authentication and Kerberos authentication can be used, the WAS administrator must first create a Kerberos keytab file on the host that is running WAS.

To create an SPN, do the following:

  1. The Kerberos ID (KERBNAME) must be of the form <service>/<fully qualified system name>.

  2. The following example creates the Kerberos SPN for SPNEGO Web, HTTP/host1.pok.ibm.com:

    ALTUSER ASCR1 KERB(KERBNAME(HTTP/host1.pok.ibm.com))
    

  3. Generate the Kerberos key for this user. To generate this key, a password must be associated with this ID. You should not allow this ID to log onto the system. Enter the following two lines whenever a new Kerberos key is required.

    The WebSphere or KDC administrator must know this password to create an entry in the keytab file.

    ALTUSER ASCR1 PASSWORD(was1krb) NOEXPIRED ALTUSER ASCR1 NOPASSWORD
    

  4. Verify that this user has a valid Kerberos segment and a key. For example:

    LISTUSER ASCR1 KERB NORACF
    

    USER=ASCR1

    KERB INFORMATION ----------------

    KERBNAME= HTTP/host1.pok.ibm.com

    KEY VERSION= 001

    KEY ENCRYPTION TYPE= DES NODES3 NODESD

    To create a Kerberos keytab (krb5.keytab) file, use the Java Kerberos ktab command, <$WAS_HOME>/java/bin/ktab, by doing the following:

  5. From a command line, type the ktab –help command to obtain the proper usage for this command. For example:

    (host1)CTC03:/PYRSA1/usr/lpp/zWebSphere/V7R1/java/J5.0/bin(189):>ktab -help Usage: java com.ibm.security.krb5.internal.tools.Ktab [options] Available options:
            -l          list the keytab name and entries
            -a <principal_name> [password]   add an entry to the keytab
            -d <principal_name>        delete an entry from the keytab
            -k <keytab_name>      specify keytab name and path with FILE: prefix
            -m <source_keytab_name> <destination_keytab_name>      specify merging source keytab file name and destination keytab file name
       
    

  6. Also from a command line, use the ktab command to add the SPN to a default keytab file. For example:

    (host1)CTC03:/PYRSA1/usr/lpp/zWebSphere/V7R1/java/J5.0/bin(201):>ktab -a HTTP/host1.pok.ibm.com@LSREALM.POK.IBM.COM ot56prod Done! Service key for principal HTTP/host1.pok.ibm.com@LSREALM.POK.IBM.COM saved
    

  7. Verify that the correct SPN is in the default keytab file. For example:

    (host1)CTC03:/PYRSA1/usr/lpp/zWebSphere/V7R1/java/J5.0/bin(202):>ktab
    1 entries in keytab, name: /etc/skrb/krb5.keytab
            KVNO    Principal
            ----    ---------
            1       HTTP/host1.pok.ibm.com@LSREALM.POK.IBM.COM
    
Make the keytab file available to WAS. Copy the krb5.keytab file from the KDC to the WAS machine at the location specified in the Kerberos configuration file (krb5.ini or krb5.conf). For example:

ftp> bin ftp> put c:\temp\KRB5_NT_SEV_HST\krb5.keytab

A Kerberos keytab configuration file contains a list of keys that are analogous to user passwords. It is important for hosts to protect their Kerberos keytab files by storing them on the local disk, which makes them readable only by authorized users. Use the validateKrbConfig command to validate the krb5.conf and krb5.keytab files. For example:

wsadmin>$AdminTask help validateKrbConfig 

The Kerberos keytab file is shared by Kerberos and SPNEGO Web authentication. It is loaded once and cannot be refreshed.

This is not true, however, if we have the JDK 1.6 with SR3 installed.

to merge the keytab files, it is recommended that you use the Java ktab command with the -m option.

 

Results

we have created a Kerberos service principal and keytab file on the KDC that WAS uses to process SPNEGO and or Kerberos authentication requests.

 

Related concepts


Kerberos (KRB5) authentication mechanism support for security

 

Related tasks


Create a single sign-on for HTTP requests using SPNEGO Web authentication
Set Kerberos as the authentication mechanism

 

Related


Kerberos authentication
Ktab - Kerberos Key Table Manager
Kerberos: The Network Authentication Protocol