6
Configuring Kerberos Authentication

This chapter describes how to configure Oracle Advanced Security for Oracle Database for use with Kerberos authentication--and how to configure Kerberos to authenticate Oracle database users. This chapter contains the following topics:

• Enabling Kerberos Authentication
• Utilities for the Kerberos Authentication Adapter
• Configuring Interoperability with a Windows 2000 Domain Controller KDC
• Troubleshooting

Enabling Kerberos Authentication

To enable Kerberos authentication:

• Task 1: Install Kerberos
• Task 2: Configure a Service Principal for an Oracle Database Server
• Task 3: Extract a Service Table from Kerberos
• Task 4: Install an Oracle Database Server and an Oracle Client
• Task 5: Install Oracle Net Services and Oracle Advanced Security
• Task 6: Configure Oracle Net Services and Oracle Database
• Task 7: Configure Kerberos Authentication
• Task 8: Create a Kerberos User
• Task 9: Create an Externally Authenticated Oracle User
• Task 10: Get an Initial Ticket for the Kerberos/Oracle User

Task 1: Install Kerberos

Install Kerberos on the system that functions as the authentication server.

Task 2: Configure a Service Principal for an Oracle Database Server

To enable the Oracle database server to validate the identity of clients that authenticate themselves using Kerberos, you must create a service principal for Oracle Database.

The name of the principal should have the following format:

kservice/kinstance@REALM

Each of the fields in the service principal specify the following values:

Service Principal Field	Description
kservice	A case-sensitive string that represents the Oracle service; this can be the same as the database service name.
kinstance	This is typically the fully qualified name of the system on which Oracle Database is running.
REALM	The domain name of the database server. REALM must always be uppercase and is typically the DNS domain name.

For example, if kservice is oracle, the fully qualified name of the system on which Oracle Database is running is dbserver.someco.com and the realm is SOMECO.COM. The principal name is:

oracle/dbserver.someco.com@SOMECO.COM

It is a convention to use the DNS domain name as the name of the realm. To create the service principal, run kadmin.local. On UNIX, run this command as the root user, by using the following syntax:

# cd /kerberos-install-directory/sbin
# ./kadmin.local

To add a principal named oracle/dbserver.someco.com@SOMECO.COM to the list of server principals known by Kerberos, enter the following:

kadmin.local:addprinc -randkey oracle/dbserver.someco.com@SOMECO.COM

Task 3: Extract a Service Table from Kerberos

Extract the service table from Kerberos and copy it to the Oracle database server/Kerberos client system.

For example, use the following steps to extract a service table for dbserver.someco.com:

1. Enter the following to extract the service table:

   kadmin.local:  ktadd -k /tmp/keytab oracle/dbserver.someco.com
   
   Entry for principal oracle/dbserver.someco.com with kvno 2, encryption 
   DES-CBC-CRC added to the keytab WRFILE: 'WRFILE:/tmp/keytab
   
   kadmin.local:  exit
   
   oklist -k -t /tmp/keytab
   
   

2. After the service table has been extracted, verify that the new entries are in the table in addition to the old ones. If they are not, or you need to add more, use kadmin.local to append to them.

   If you do not enter a realm when using ktadd, it uses the realm of the current host and displays it in the command output, as shown in Step 1.

3. If the Kerberos service table is on the same system as the Kerberos client, you can move it. If the service table is on a different system from the Kerberos client, you must transfer the file with a program such as FTP. If using FTP, transfer the file in binary mode.

   The following example shows how to move the service table on a UNIX platform:

   # mv /tmp/keytab /etc/v5srvtab
   
   

   The default name of the service file is /etc/v5srvtab.

4. Verify that the owner of the Oracle database server executable can read the service table (/etc/v5srvtab in the previous example). To do so, set the file owner to the Oracle user, or make the file readable by the group to which Oracle belongs.

   Caution: Do not make the file readable to all users. This can cause a security breach.

Task 4: Install an Oracle Database Server and an Oracle Client

Install the Oracle database server and client software.

Task 5: Install Oracle Net Services and Oracle Advanced Security

Install Oracle Net Services and Oracle Advanced Security on the Oracle database server and Oracle client systems.

Task 6: Configure Oracle Net Services and Oracle Database

Configure Oracle Net Services on the Oracle database server and client.

Task 7: Configure Kerberos Authentication

Perform these tasks to set required parameters in the Oracle database server and client sqlnet.ora files:

• Step 1: Configure Kerberos on the Client and on the Database Server
• Step 2: Set the Initialization Parameters
• Step 3: Set sqlnet.ora Parameters (optional)

Step 1: Configure Kerberos on the Client and on the Database Server

Use Oracle Net Manager to perform the following steps to configure Kerberos authentication service parameters on the client and on the database server (See "Starting Oracle Net Manager"):

1. Navigate to the Oracle Advanced Security profile. ( See "Navigating to the Oracle Advanced Security Profile") The Oracle Advanced Security window appears (Figure 6-1):

Figure 6-1 Oracle Advanced Security Authentication Window (Kerberos)

Text description of the illustration kerb0001.gif

2. Choose the Authentication tab.
3. From the Available Methods list, select KERBEROS5.
4. Move KERBEROS5 to the Selected Methods list by clicking the right arrow (>).
5. Arrange the selected methods in order of use. To do this, select a method in the Selected Methods list, then click Promote or Demote to position it in the list. For example, if you want KERBEROS5 to be the first service used, move it to the top of the list.
6. Choose the Other Params tab (Figure 6-2).

Figure 6-2 Oracle Advanced Security Other Params Window (Kerberos)

Text description of the illustration kerb0002.gif

7. From the Authentication Service list, select KERBEROS(V5).
8. Type Kerberos into the Service field. This field defines the name of the service Oracle Database uses to obtain a Kerberos service ticket. When you provide the value for this field, the other fields are enabled.
9. Optionally enter values for the following fields:
   • Credential Cache File
   • Configuration File
   • Realm Translation File
   • Key Table
   • Clock Skew

     See Also: Oracle Net Manager online help, and "Step 3: Set sqlnet.ora Parameters (optional)", for more information about the fields and the parameters they configure

10. Choose File > Save Network Configuration.

    The sqlnet.ora file is updated with the following entries:

    SQLNET.AUTHENTICATION_SERVICES=(KERBEROS5)
    SQLNET.AUTHENTICATION_KERBEROS5_SERVICE=kservice
    
    

Step 2: Set the Initialization Parameters

To set parameters in the initialization parameter file:

1. Add the following parameter to the initialization parameter file:

   REMOTE_OS_AUTHENT=FALSE
   
   

   Caution: Setting REMOTE_OS_AUTHENT to TRUE can enable a security breach, because it lets someone using a non-secure protocol, such as TCP, perform an operating system-authorized login (formerly called an OPS$ login).

2. Because Kerberos user names can be long, and Oracle user names are limited to 30 characters, Oracle Corporation strongly recommends that you set the value of OS_AUTHENT_PREFIX to null as follows:

   OS_AUTHENT_PREFIX=""
   
   

   Setting this parameter to null overrides the default value of OPS$.

Step 3: Set sqlnet.ora Parameters (optional)

In addition to the required parameters, you can optionally set the following parameters in the sqlnet.ora file on the client and the Oracle database server:

Parameter:	SQLNET.KERBEROS5_CC_NAME=pathname_to_credentials_cache_file
Description:	Specifies the complete path name to the Kerberos credentials cache (CC) file. The default value is operating system-dependent. For UNIX, it is /tmp/krb5cc_userid. You can also set this parameter by using the KRB5CCNAME environment variable, but the value set in the sqlnet.ora file takes precedence over the value set in KRB5CCNAME.
Example:	SQLNET.KERBEROS5_CC_NAME=/usr/tmp/krbcache
Parameter:	SQLNET.KERBEROS5_CLOCKSKEW=number_of_seconds_accepted_as_network_delay
Description:	This parameter specifies how many seconds can pass before a Kerberos credential is considered out-of-date. It is used when a credential is actually received by either a client or a database server. An Oracle database server also uses it to decide if a credential needs to be stored to protect against a replay attack. The default is 300 seconds.
Example:	SQLNET.KERBEROS5_CLOCKSKEW=1200
Parameter:	SQLNET.KERBEROS5_CONF=pathname_to_Kerberos_ configuration_file
Description:	This parameter specifies the complete path name to the Kerberos configuration file. The configuration file contains the realm for the default KDC (key distribution center) and maps realms to KDC hosts. The default is operating system-dependent. For UNIX, it is /krb5/krb.conf.
Example:	SQLNET.KERBEROS5_CONF=/krb/krb.conf
Parameter:	SQLNET.KERBEROS5_CONF_MIT=[TRUE|FALSE]
Description:	This parameter specifies whether the new MIT Kerberos configuration format is used. If the value is set to TRUE, it will parse the file according to the new configuration format rules. When the value is set to FALSE, the default (non-MIT) configuration is used. The default is FALSE.
Example:	SQLNET.KERBEROS5_CONF_MIT=False
Parameter:	SQLNET.KERBEROS5_KEYTAB= pathname_to_Kerberos_principal/key_table
Description:	This parameter specifies the complete path name to the Kerberos principal/secret key mapping file. It is used by the Oracle database server to extract its key and decrypt the incoming authentication information from the client. The default is operating system-dependent. For UNIX, it is /etc/v5srvtab.
Example:	SQLNET.KERBEROS5_KEYTAB=/etc/v5srvtab
Parameter:	SQLNET.KERBEROS5_REALMS= pathname_to_Kerberos_realm_translation_file
Description:	This parameter specifies the complete path name to the Kerberos realm translation file. The translation file provides a mapping from a host name or domain name to a realm. The default is operating system-dependent. For UNIX, it is /etc/krb.realms.
Example:	SQLNET.KERBEROS5_REALMS=/krb5/krb.realms

Task 8: Create a Kerberos User

To create Oracle users that Kerberos can authenticate, perform this task on the Kerberos authentication server where the administration tools are installed. The realm must already exist.

Run /krb5/admin/kadmin.local as root to create a new Kerberos user, such as krbuser.

The following example is UNIX-specific:

# ./kadmin.local
kadmin.local: addprinc krbuser
Enter password for principal: "krbuser@SOMECO.COM": (password does not display)
Re-enter password for principal: "krbuser@SOMECO.COM": (password does not 
display)
kadmin.local: exit

Task 9: Create an Externally Authenticated Oracle User

Run SQL*Plus on the Oracle database server to create the Oracle user that corresponds to the Kerberos user. In the following example, OS_AUTHENT_PREFIX is set to null (""). The Oracle user name is in uppercase enclosed in double quotation marks as shown in the following example:

SQL> CONNECT / AS SYSDBA;
SQL> CREATE USER "KRBUSER@SOMECO.COM" IDENTIFIED EXTERNALLY; 
SQL> GRANT CREATE SESSION TO "KRBUSER@SOMECO.COM"; 

Task 10: Get an Initial Ticket for the Kerberos/Oracle User

Before you can connect to the database, you must ask the Key Distribution Center (KDC) for an initial ticket. To do so, run the following on the client:

% okinit username

If, when making a database connection, a reference such as the following follows a database link, you must use the forwardable flag (-f) option:

sqlplus /@oracle

Executing okinit -f enables credentials that can be used across database links. Run the following commands on the Oracle client:

% okinit -f
Password for krbuser@SOMECO.COM:password

Utilities for the Kerberos Authentication Adapter

Three utilities are shipped with the Oracle Kerberos authentication adapter. These utilities are intended for use on an Oracle client with Oracle Kerberos authentication support installed. Use the following utilities for these specified tasks:

• Obtaining the Initial Ticket with the okinit Utility
• Displaying Credentials with the oklist Utility
• Removing Credentials from the Cache File with the okdstry Utility

Obtaining the Initial Ticket with the okinit Utility

The okinit utility obtains and caches Kerberos tickets. This utility is typically used to obtain the ticket-granting ticket, using a password entered by the user to decrypt the credential from the key distribution center (KDC). The ticket-granting ticket is then stored in the user's credential cache.

The options available with okinit are listed in Table 6-1:

Table 6-1 Options for the okinit Utility

Option	Description
-f	Ask for a forwardable ticket-granting ticket. This option is necessary to follow database links.
-l	Specify the lifetime of the ticket-granting ticket and all subsequent tickets. By default, the ticket-granting ticket is good for eight (8) hours, but shorter or longer-lived credentials may be desired. Note that the KDC can ignore this option or put site-configured limits on what can be specified. The lifetime value is a string that consists of a number qualified by w (weeks), d (days), h (hours), m (minutes), or s (seconds), as in the following example: okinit -l 2wld6h20m30s The example requests a ticket-granting ticket that has a life time of 2 weeks, 1 day, 6 hours, 20 minutes, and 30 seconds.
-c	Specify an alternative credential cache. For UNIX, the default is /tmp/krb5cc_uid. You can also specify the alternate credential cache by using the SQLNET.KERBEROS5_CC_NAME parameter in the sqlnet.ora file.
-?	List command line options.

Displaying Credentials with the oklist Utility

Run the oklist utility to display the list of tickets held; available oklist options are listed in Table 6-2:

Table 6-2 Options for the oklist Utility

Option	Description
-f	Show flags with credentials. Relevant flags are I, credential is a ticket-granting ticket, F, credential is forwardable, and f, credential is forwarded.
-c	Specify an alternative credential cache. In UNIX, the default is /tmp/krb5cc_uid. The alternate credential cache can also be specified by using the SQLNET.KERBEROS5_CC_NAME parameter in the sqlnet.ora file.
-k	List the entries in the service table (default /etc/v5srvtab) on UNIX. The alternate service table can also be specified by using the SQLNET.KERBEROS5_KEYTAB parameter in the sqlnet.ora file.

The show flag option (-f) displays additional information, as shown in the following example:

% oklist -f
27-Jul-1999 21:57:51   28-Jul-1999 05:58:14
krbtgt/SOMECO.COM@SOMECO.COM
Flags: FI

Removing Credentials from the Cache File with the okdstry Utility

Use the okdstry utility to remove credentials from the credentials cache file:

$ okdstry -f

where the -f command option lets you specify an alternative credential cache. For UNIX, the default is /tmp/krb5cc_uid. You can also specify the alternate credential cache by using the SQLNET.KRB5_CC_NAME parameter in the sqlnet.ora file.

Connecting to an Oracle Database Server Authenticated by Kerberos

You can now connect to an Oracle database server without using a user name or password. Enter a command similar to the following:

$ sqlplus /@net_service_name

where net_service_name is an Oracle Net Services service name. For example:

$ sqlplus /@oracle_dbname

Configuring Interoperability with a Windows 2000 Domain Controller KDC

Oracle Advanced Security, which complies with MIT Kerberos, can interoperate with tickets that are issued by a Kerberos Key Distribution Center (KDC) on a Windows 2000 domain controller to enable Kerberos authentication with an Oracle database. To configure Kerberos authentication that uses a Windows 2000 domain controller KDC, perform the following tasks:

• Task 1: Configuring an Oracle Kerberos Client to Interoperate with a Windows 2000 Domain Controller KDC
• Task 2: Configuring a Windows 2000 Domain Controller KDC to Interoperate with an Oracle Client
• Task 3: Configuring an Oracle Database to Interoperate with a Windows 2000 Domain Controller KDC
• Task 4: Getting an Initial Ticket for the Kerberos/Oracle User

Task 1: Configuring an Oracle Kerberos Client to Interoperate with a Windows 2000 Domain Controller KDC

The following steps must be performed on the Oracle Kerberos client.

Step 1: Creating Client Kerberos Configuration Files to Use a Windows Domain Controller KDC

Create the following Kerberos client configuration files that refer to the Windows 2000 domain controller as the Kerberos KDC. In the examples that follow, the Windows 2000 domain controller is running on a node named sales3854.us.acme.com.

• krb.conf file

  For example:

  SALES3854.US.ACME.COM
  SALES3854.US.ACME.COM sales3854.us.acme.com admin server
  
  

• krb5.conf file

  For example:

  [libdefaults]
  default_realm=SALES.US.ACME.COM
  [realms]
  SALES.US.ACME.COM= {
  

  kdc=sales3854.us.acme.com:88
  }
  

  [domain_realm]
  .us.acme.com=SALES.US.ACME.COM
  
  

• krb5.realms file

  For example:

  us.acme.com SALES.US.ACME.COM
  
  

Step 2: Specifying Oracle Configuration Parameters in the sqlnet.ora File

Configuring an Oracle client to interoperate with a Windows 2000 domain controller KDC uses the same sqlnet.ora file parameters that are listed in "Step 1: Configure Kerberos on the Client and on the Database Server".

Set the following parameters in the sqlnet.ora file on the client:

SQLNET.KERBEROS5_CONF=pathname_to_Kerberos_configuration_file
SQLNET.KERBEROS5_CONF_MIT=TRUE
SQLNET.AUTHENTICATION_KERBEROS5_SERVICE=Kerberos_service_name
SQLNET.AUTHENTICATION_SERVICES=(BEQ,KERBEROS5)

Step 3: Specifying the Listening Port Number

The Windows 2000 domain controller KDC listens on UDP/TCP port 88. Ensure that the system file entry for kerberos5 is set to UDP/TCP port 88 as follows:

• (UNIX)

  Ensure that the kerberos5 entry in the /etc/services file is set to 88

Task 2: Configuring a Windows 2000 Domain Controller KDC to Interoperate with an Oracle Client

The following steps must be performed on the Windows 2000 domain controller.

Step 1: Creating the User

Create a new user for the Oracle client in Microsoft Active Directory.

Step 2: Creating the Oracle Database Principal

1. Create a new user for the Oracle database in Microsoft Active Directory.

   For example, if the Oracle database runs on the host sales3854.us.acme.com, then use Active Directory to create a user with the username sales3854.us.acme.com and the password oracle.

   Note: Do not create a user as host/hostname.dns.com, such as oracle/sales3854.us.acme.com, in Active Directory. Microsoft's KDC does not support multipart names like an MIT KDC does. An MIT KDC allows multipart names to be used for service principals because it treats all principals as usernames. However, Microsoft's KDC does not.

2. Use the Ktpass command line utility to extract the keytab file with the following syntax:

   Ktpass -princ service/hostname@NT-DNS-REALM-NAME -mapuser account -pass 
   password -out keytab.file
   
   

Using the database user created in the previous step, the following is an example of Ktpass usage:

C:> Ktpass -princ oracle/sales3854.us.acme.com@SALES.US.COM -mapuser 
sales3854 -pass oracle -out C:\temp\v5srvtab

This utility is part of the Windows 2000 Support Tools and can be found on the Windows 2000 distribution media in the \support\reskit\netmgmt\security folder.

• Copy the extracted keytab file to the host computer where the Oracle database is installed.

  For example, the keytab that was created in the previous step can be copied to /krb5/v5svrtab.

  See Also: Detailed information about Windows 2000 interoperability with Kerberos 5 that is available at the following URL: http://www.microsoft.com/WINDOWS2000/techinfo/planning/security/ kerbsteps.asp

Task 3: Configuring an Oracle Database to Interoperate with a Windows 2000 Domain Controller KDC

The following steps must be performed on the host computer where the Oracle database is installed.

Step 1: Setting Configuration Parameters in the sqlnet.ora File

Specify values for the following parameters in the sqlnet.ora file for the database server:

SQLNET.KERBEROS5_CONF=pathname_to_Kerberos_configuration_file
SQLNET.KERBEROS5_KEYTAB=pathname_to_Kerberos_principal/key_table
SQLNET.KERBEROS5_CONF_MIT=TRUE
SQLNET.AUTHENTICATION_KERBEROS5_SERVICE=Kerberos_service_name
SQLNET.AUTHENTICATION_SERVICES=(BEQ,KERBEROS5)

Step 2: Creating an Externally Authenticated Oracle User

Follow the task information for "Task 9: Create an Externally Authenticated Oracle User" to create an externally authenticated Oracle user. Ensure that the username is created in all uppercase characters. For example, ORAKRB@SALES.US.ACME.COM.

Task 4: Getting an Initial Ticket for the Kerberos/Oracle User

Before a client can connect to the database, the client must request an initial ticket. To request an initial ticket, follow the task information for "Task 10: Get an Initial Ticket for the Kerberos/Oracle User".

Troubleshooting

This section lists some common configuration problems and explains how to resolve them.

• If you cannot get your ticket-granting ticket using OKINIT:
  • Ensure that the default realm is correct by examining the krb.conf file.
  • Ensure that the KDC is running on the host specified for the realm.
  • Ensure that the KDC has an entry for the user principal and that the passwords match.
  • Ensure that the krb.conf and krb.realms files are readable by Oracle.
• If you have an initial ticket, but still cannot connect:
  • After trying to connect, check for a service ticket.
  • Check that the sqlnet.ora file on the database server side has a service name that corresponds to a service known by Kerberos.
  • Check that the clocks on all systems involved are set to times that are within a few minutes of each other (or change the SQLNET.KERBEROS5_CLOCKSKEW parameter in the
    sqlnet.ora file).
• If you have a service ticket and you still cannot connect:
  • Check the clocks on the client and database server.
  • Check that the v5srvtab file exists in the correct location and is readable by Oracle (remember to set the sqlnet.ora parameters).
  • Check that the v5srvtab file has been generated for the service named in the sqlnet.ora file on the database server side.
• If everything seems to work fine, but then you issue another query and it fails:
  • Check that the initial ticket is forwardable. (You must have obtained the initial ticket by running the okinit utility.)
  • Check the expiration date on the credentials. If the credentials have expired, then close the connection and run okinit to get a new initial ticket.