6
Configuring Kerberos Authentication

This chapter describes how to configure Oracle Advanced Security for Oracle8i, or for the Oracle8i server, for use with Kerberos authentication, and how to configure Kerberos to authenticate Oracle database users. This chapter contins the following sections:

• Enabling Kerberos Authentication

• Utilities for the Kerberos Authentication Adapter

• Troubleshooting

• 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 Net8 and Oracle Advanced Security

• Task 6: Configure Net8 and Oracle

• 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

See Also: Related Documents , for information about how to install Kerberos

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 Oracle8i.

The name of the principal should have the following format:

kservice/kinstance@REALM

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 Oracle8i 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 Oracle8i 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. The following example is UNIX-specific (enter as root user):

# 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, to extract a service table for dbserver.someco.com:

1. Enter the following:

   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 the 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 above.

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 is UNIX-specific.

   # 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 allow a security breach.

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

Install the Oracle database server and client software.

See Also: Oracle8i operating system specific documentation

Task 5: Install Net8 and Oracle Advanced Security

Install Net8 and Oracle Advanced Security on the Oracle database server and Oracle client systems.

See Also: Oracle8i operating system specific installation documentation

Task 6: Configure Net8 and Oracle

Configure Net8 on the Oracle database server and client.

See Also: Oracle8i operating system specific installation documentation Net8 Administrator's Guide.

Task 7: Configure Kerberos Authentication

Perform these tasks to set certain 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

Perform the following steps to configure Kerberos authentication service parameters on the client and on the database server:

1. Start Net8 Assistant:
   • On UNIX, run netasst from $ORACLE_HOME/bin.

   • On Windows NT, choose Start > Programs > Oracle - HOME_NAME > Network Administration > Net8 Assistant.

2. In the Navigator window, expand Local > Profile.

3. From the list in the right pane, select Oracle Advanced Security.

   The Oracle Advanced Security tabbed window appears:

   
   
4. Choose the Authentication tab.

5. From the Available Methods list, select KERBEROS5.

6. Move KERBEROS5 to the Selected Methods list by clicking the right-arrow [>].

7. 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.

8. Choose the Other Params tab.

   
   

9. From the Authentication Service list, select KERBEROS(V5).

10. The Service field defines the name of the service Oracle8i uses to obtain a Kerberos service ticket; enter Kerberos. When you provide the value for this field, the other fields are enabled.

11. Optionally enter values for the following fields:
    • Credential Cache File

    • Configuration File

    • Realm Translation File

    • Key Table

    • Clock Skew

      See Also: Net8 Assistant online help, and Step 3: Set sqlnet.ora Parameters (optional), for more information about the fields and the parameters they configure

12. 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

   Attention: Setting REMOTE_OS_AUTHENT to TRUE can allow a security breach, because it allows someone using a non-secure protocol, such as TCP, to perform an operating system-authorized login (formerly referred to as 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 sqlnet.ora parameters on the client and the Oracle database server:

Parameter:	SQLNET.KERBEROS5_CC_NAME=pathname_to_credentials_cache_file
Description:	Specifies the complete pathname to the Kerberos credentials cache (CC) file. The default value is operating system-dependent. For UNIX, it is /tmp/krb5cc_user id. 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 pathname 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 will be 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 pathname 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 pathname 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.

Note: The utility names in this section are executable programs. However, the Kerberos user name krbuser and realm SOMECO.COM are examples only; they can vary among systems.

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.

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 user_name

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 okinit to obtain an initial ticket.

• Use oklist to display credentials

• Use okdstry to remove credentials from the credentials cache.

  Note: Solaris is shipped with Kerberos version 4. Ensure that the Kerberos version 5 utilities are in the path so that the version 4 utilities are not used inadvertently.

Use okinit to Obtain the Initial Ticket

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 (months), 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.

Use OKLIST to Display Credentials

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

Use OKDSTRY to Remove Credentials from the Cache File

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 a Net8 service name. For example:

$ sqlplus /@oracle_dbname

See Also: Chapter 1, Introduction to Oracle Advanced Security, for information about external authentication and Oracle8i Distributed Database Systems

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 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 see 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, close the connection and run okinit to get a new initial ticket.