Creating a Kerberos service principal name and keytab file

This task is necessary to process SPNEGO web or Kerberos authentication requests to WebSphere® Application Server. You can create a Kerberos service principal name and keytab file by using Microsoft Windows, IBM i, Linux®, Solaris, Massachusetts Institute of Technology (MIT) and z/OS® operating systems key distribution centers (KDCs).

About this task

The KDC that you use to create a Kerberos service principal name and keytab file depends on your operating system. Choose the KDC that matches your operating system:

Procedure

  • Create a Kerberos service principal name and keytab file by using Microsoft Windows KDC:
    This task is performed on the active directory domain controller machine. Complete the following steps to ensure that the Windows Server that is running the active directory domain controller is configured properly to the associated KDC.
    1. Create a user account in the Microsoft Active Directory for the WebSphere Application Server:

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

        Use the name for WebSphere Application Server. For example, if the application server you are running on the WebSphere Application Server machine is called myappserver.austin.ibm.com, create a new user in an active directory called myappserver.

      2. Make sure that you do not have the computer name myappserver under Computers and Domain Controllers. If you already have a computer named myappserver, then you must 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:>setspn -S HTTP/myappserver.austin.ibm.com myappserver
      Note: The host name must be a fully-qualified host name.
    3. Use the ktpass tool 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 you are using.
      For more information on the ktpass tool, see the ktpass command.
      Note: 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.

      To determine the appropriate parameter values for the ktpass tool, run the ktpass -? command from the command line. This command lists the encryption types supported by the ktpass tool.

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

      The following code is from ktpass /? from Windows 2016.

      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 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 : aes128-cts-hmac-sha1-96 : 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 Version Number                          
                     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                     
[- /]      RawSalt : raw salt to use when generating key (not needed)
[- +]     DumpSalt : show us the MIT salt being used to generate the key
[- +]       SetUpn : Set the UPN in addition to the SPN. Default DO.
[- +]      SetPass : Set the user's password if supplied.
      Important: Do not use the -pass switch on the ktpass command to reset a password for a Microsoft Windows server account.
      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 your Microsoft Windows environment.
      • For the following example, from a command prompt, run the ktpass command:
        ktpass -out c:\temp\myappserver.keytab
-princ HTTP/myappserver.austin.ibm.com@WSSEC.AUSTIN.IBM.COM
-mapUser myappserv 
-mapOp set 
-pass was1edu
-crypto AES256-SHA1 
-pType KRB5_NT_PRINCIPAL
        Table 1. Using ktpass for a single DES encryption type .

        This table describes how to use 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.austin.ibm.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 AES256-SHA1
        • This option is the recommended encryption type.
        • DES encryption types might cause a security warning as they are less secure.
        • Users can adjust the encryption type such as -crypto AES256-SHA1|AES128-SHA1
        -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 SPNEGO.
        Important:

        When you are mapping your SPN(s), map a maximum of 1 SPN to an individual AD user. If want to map multiple SPNs to an individual AD user, ensure that the Microsoft ktpass tool supports the steps that you are following.

        You might see the following message:
        [JGSS_DBG_CTX]  WebContainer : 0 Error authenticating request. Reporting to client
Major code = 11, Minor code = 0
org.ietf.jgss.GSSException, major code: 11, minor code: 0
	major string: General failure, unspecified at GSSAPI level
	minor string: Kerberos error while decoding and verifying token: com.ibm.security.krb5.internal.crypto.KrbCryptoException, status code: 0
	message: com.ibm.security.krb5.internal.KrbException, status code: 31
	message: Integrity check on decrypted field failed
        If you see this message, ensure that the following information is correct:
        • The current user password matches the one that was defined when the keytab was generated.
        • You are using the latest release of the ktpass tool from Microsoft.
        • You are using the latest fix pack for the application server and the latest JDK version.
        If the previous recommendations do not resolve the issue, contact Microsoft to proceed with further debug.
  • Create a Kerberos service principal name and keytab file by using iSeries, Linux, Solaris and MIT KDCs:

    See your 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 a MIT KDC machine.

    1. Create a Kerberos service principal for Kerberos authentication, for example: 
      WAS/testmach.austin.ibm.com 
kadmin.local: addprinc WAS/testmach.austin.ibm.com
    2. Add the newly-created Kerberos service principal, WAS/testmach.austin.ibm.com to a default krb5.keytab file, for example: 
      kadmin.local: ktadd WAS/testmach.austin.ibm.com
  • [z/OS]Create a Kerberos service principal name and keytab file using z/OS KDC:

    Before Simple and Protected GSS-API Negotiation (SPNEGO) web authentication and Kerberos authentication can be used, the WebSphere Application Server administrator must first create a Kerberos keytab file on the host that is running WebSphere Application Server.

    To create an SPN, complete the following steps:

    1. The Kerberos ID (KERBNAME) must be of the form <service>/<fully qualified system name>.
      The following example creates the Kerberos SPN for SPNEGO Web, HTTP/host1.pok.ibm.com:
      ALTUSER ASCR1 KERB(KERBNAME(HTTP/host1.pok.ibm.com))
      Avoid trouble: You should ensure that the list of supported encryption types specified on the ALTUSER command is consistent with what is specified in the krb5.conf kerberos configuration file. For example, if the krb5.conf configuration file specifies that only aes256-cts-hmac-sha1-96 is supported, then the ENCRYPT operand should have all encryption types set as not supported, except for AES256.
    2. Generate the Kerberos key for this user.
      To generate this key, a password must be associated with this ID. Do not use this ID to log onto the system. Enter the following two lines whenever a new Kerberos key is required:
      ALTUSER ASCR1 PASSWORD(was1krb) NOEXPIRED
ALTUSER ASCR1 NOPASSWORD
      Note: The WebSphere or KDC administrator must know this password to create an entry in the keytab file.
    3. 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 continuing with the next step. The Java Kerberos ktab command is available only for IBM JDK 1.8 and older versions.

    4. 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
    5. 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
    6. 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 WebSphere Application Server. Copy the krb5.keytab file from the KDC to the WebSphere Application Server 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
      Note: 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
      Note: The Kerberos keytab file is shared by Kerberos and SPNEGO web authentication, and LDAP bind authentication. It is loaded once and cannot be refreshed.
      Note: You can also use the MS ktpass command to include an existing keytab file with the newly created keytab by using the -in option. The following example command includes the myOtherKrb5.keytab keytab. 
      ktpass -in myOtherKrb5.keytab -out krb5.keytab -princ HTTP/myLibertyMachine.example.com@MYDOMAIN.EXAMPLE.COM -mapUser myLibertyMachine_http -mapOp set -pass security -crypto aes128-cts-hmac-sha1-96 -ptype KRB5_NT_PRINCIPAL
      The example command produces the following output.
      Targeting domain controller: myAdMachine.MYDOMAIN.EXAMPLE.COM
Using legacy password setting method
Successfully mapped HTTP/myLibertyMachine.example.com to myLibertyMachine_http.
Key created.
Output keytab to krb5.keytab:
Keytab version: 0x502
keysize 93 HTTP/myLibertyMachine.example.com@MYDOMAIN.EXAMPLE.COM ptype 1 (KRB5_NT_PRINCIPAL) vno 3 etype 0x17 (aes128-cts-hmac-sha1-96) keylength 16 (0x148d643db283327d3f3d44547da8cade)

Results

You have created a Kerberos service principal name and keytab file on the KDC that WebSphere Application Server uses to process SPNEGO and or Kerberos authentication requests.