kdc.conf(4) (man pages section 4: File Formats)

man pages section 4: File Formats

kdc.conf(4)

Name

kdc.conf– Key Distribution Center (KDC) configuration file

Synopsis

/etc/krb5/kdc.conf

Description

The kdc.conf file contains KDC configuration information, including defaults used when issuing Kerberos tickets. This file must reside on all KDC servers. After you make any changes to the kdc.conf file, stop and restart the krb5kdc daemon on the KDC for the changes to take effect.

The format of the kdc.conf consists of section headings in square brackets ([]). Each section contains zero or more configuration variables (called relations), of the form of:

relation = relation-value

relation-subsection = {
     relation = relation-value
     relation = relation-value
     }

The kdc.conf file contains one of more of the following three sections:

kdcdefaults: Contains default values for overall behavior of the KDC.
realms: Contains subsections for Kerberos realms, where relation-subsection is the name of a realm. Each subsection contains relations that define KDC properties for that particular realm, including where to find the Kerberos servers for that realm.
logging: Contains relations that determine how Kerberos programs perform logging.

The `kdcdefaults` Section

The following relation can be defined in the [kdcdefaults] section:

kdc_ports: This relation lists the UDP ports on which the Kerberos server should listen by default. This list is a comma-separated list of integers. If the assigned value is 0, the Kerberos server does not listen on any UDP port. If this relation is not specified, the Kerberos server listens on port 750 and port 88.
kdc_tcp_ports: This relation lists the TCP ports on which the Kerberos server should listen by default. This list is a comma-separated list of integers. If the assigned value is 0, the Kerberos server does not listen on any TCP port. If this relation is not specified, the Kerberos server listens on the kdc TCP port specified in /etc/services. If this port is not found in /etc/services the Kerberos server defaults to listen on TCP port 88.
kdc_max_tcp_connections: This relation controls the maximum number of TCP connections the KDC allows. The minimum value is 10. If this relation is not specified, the Kerberos server allows a maximum of 30 TCP connections.

The `realms` Section

This section contains subsections for Kerberos realms, where relation-subsection is the name of a realm. Each subsection contains relations that define KDC properties for that particular realm.

The following relations can be specified in each subsection:

acl_file

(string) Location of the Kerberos V5 access control list (ACL) file that kadmin uses to determine the privileges allowed to each principal on the database. The default location is /etc/krb5/kadm5.acl.

admin_keytab

(string) Location of the keytab file that kadmin uses to authenticate to the database. The default location is /etc/krb5/kadm5.keytab.

database_name

(string) Location of the Kerberos database for this realm. The default location is /var/krb5/principal.

default_principal_expiration

(absolute time string) The default expiration date of principals created in this realm. See the Time Format section in kinit(1) for the valid absolute time formats you can use for default_principal_expiration.

default_principal_flags

(flag string) The default attributes of principals created in this realm. Some of these flags are better to set on an individual principal basis through the use of the attribute modifiers when using the kadmin command to create and modify principals. However, some of these options can be applied to all principals in the realm by adding them to the list of flags associated with this relation.

A “flag string” is a list of one or more of the flags listed below preceded by a minus (-) or a plus (+) character, indicating that the option that follows should be enabled or disabled.

Flags below marked with an asterisk (*) are flags that are best applied on an individual principal basis through the kadmin or gkadmin interface rather than as a blanket attribute to be applied to all principals.

postdateable: Create postdatable tickets.
forwardable: Create forwardable tickets.
tgt-based: Allow TGT-based requests.
renewable: Create Renewable tickets.
proxiable: Create Proxiable tickets.
dup-skey: Allow DUP_SKEY requests, this enables user-to-user authentication.
preauth: Require the use of pre-authentication data whenever principals request TGTs.
hwauth: Require the use of hardware-based pre-authentication data whenever principals request TGTs.
* allow-tickets: Allow tickets to be issued for all principals.
* pwdchange: Require principal's to change their password.
* service: Enable or disable a service.
* pwservice: Mark principals as password changing principals.

An example of default_principal_flags is shown in EXAMPLES, below.

dict_file

(string) Location of the dictionary file containing strings that are not allowed as passwords. A principal with any password policy is not allowed to select a password in the dictionary. The default location is /var/krb5/kadm5.dict.

kadmind_port

(port number) The port that the kadmind daemon is to listen on for this realm. The assigned port for kadmind is 749.

key_stash_file

(string) Location where the master key has been stored (by kdb5_util stash). The default location is /var/krb5/.k5.realm, where realm is the Kerberos realm.

kdc_ports

(string) The list of UDP ports that the KDC listens on for this realm. By default, the value of kdc_ports as specified in the [kdcdefaults] section is used.

kdc_tcp_ports

(string) The list of TCP ports that the KDC listens on (in addition to the UDP ports specified by kdc_ports) for this realm. By default, the value of kdc_tcp_ports as specified in the [kdcdefaults] section is used.

master_key_name

(string) The name of the master key.

master_key_type

(key type string) The master key's key type. This is used to determine the type of encryption that encrypts the entries in the principal db. des-cbc-crc, des3-cbc-md5, des3-cbc-sha1-kd, arcfour-hmac-md5, arcfour-hmac-md5-exp, aes128-cts-hmac-sha1-96, and aes256-cts-hmac-sha1-96 are supported at this time (des-cbc-crc is the default). If you set this to des3-cbc-sha1-kd all systems that receive copies of the principal db, such as those running slave KDC's, must support des3-cbc-sha1-kd.

max_life

(delta time string) The maximum time period for which a ticket is valid in this realm. See the Time Format section in kinit(1) for the valid time duration formats you can use for max_life.

max_renewable_life

(delta time string) The maximum time period during which a valid ticket can be renewed in this realm. See the Time Format section in kinit(1) for the valid time duration formats you can use for max_renewable_life.

sunw_dbprop_enable = [true | false]

Enable or disable incremental database propagation. Default is false.

sunw_dbprop_master_ulogsize = N

Specifies the maximum number of log entries available for incremental propagation to the slave KDC servers. The maximum value that this can be is 2500 entries. Default value is 1000 entries.

sunw_dbprop_slave_poll = N[s, m, h]

Specifies how often the slave KDC polls for new updates that the master might have. Default is 2m (two minutes).

supported_enctypes

List of key/salt strings. The default key/salt combinations of principals for this realm. The key is separated from the salt by a colon (:) or period (.). Multiple key/salt strings can be used by separating each string with a space. The salt is additional information encoded within the key that tells what kind of key it is. Only the normal salt is supported at this time, for example, des-cbc-crc:normal. If this relation is not specified, the default setting is:

aes256-cts-hmac-sha1-96:normal \ (see note below) 
aes128-cts-hmac-sha1-96:normal \
des3-cbc-sha1-kd:normal \
arcfour-hmac-md5:normal \
des-cbc-md5:normal

Note –

The unbundled Strong Cryptographic packages must be installed for the aes256-cts-hmac-sha1-96:normal enctype to be available for Kerberos.

reject_bad_transit

This boolean specifies whether the list of transited realms for cross-realm tickets should be checked against the transit path computed from the realm names and the [capaths] section of its krb5.conf(4) file.

The default for reject_bad_transit is true.

The `logging` Section

This section indicates how Kerberos programs perform logging. The same relation can be repeated if you want to assign it multiple logging methods. The following relations can be defined in the [logging] section:

kdc: Specifies how the KDC is to perform its logging. The default is FILE:/var/krb5/kdc.log.
admin_server: Specifies how the administration server is to perform its logging. The default is FILE:/var/krb5/kadmin.log.
default: Specifies how to perform logging in the absence of explicit specifications.

The [logging] relations can have the following values:

FILE:filename

FILE=filename

This value causes the entity's logging messages to go to the specified file. If the `=' form is used, the file is overwritten. If the `:' form is used, the file is appended to.

STDERR

This value sends the entity's logging messages to its standard error stream.

CONSOLE

This value sends the entity's logging messages to the console, if the system supports it.

DEVICE=devicename

This sends the entity's logging messages to the specified device.

SYSLOG[:severity[:facility]]

This sends the entity's logging messages to the system log.

The severity argument specifies the default severity of system log messages. This default can be any of the following severities supported by the syslog(3C) call, minus the LOG_ prefix: LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, and LOG_DEBUG. For example, a value of CRIT would specify LOG_CRIT severity.

The facility argument specifies the facility under which the messages are logged. This can be any of the following facilities supported by the syslog(3C) call minus the LOG_ prefix: LOG_KERN, LOG_USER, LOG_MAIL, LOG_DAEMON, LOG_AUTH, LOG_LPR, LOG_NEWS, LOG_UUCP, LOG_CRON, and LOG_LOCAL0 through LOG_LOCAL7.

If no severity is specified, the default is ERR. If no facility is specified, the default is AUTH.

In the following example, the logging messages from the KDC go to the console and to the system log under the facility LOG_DAEMON with default severity of LOG_INFO; the logging messages from the administration server are appended to the /var/krb5/kadmin.log file and sent to the /dev/tty04 device.

[logging]
kdc = CONSOLE
kdc = SYSLOG:INFO:DAEMON
admin_server = FILE:/export/logging/kadmin.log
admin_server = DEVICE=/dev/tty04

PKINIT-specific Options

The following are pkinit-specific options. These values can be specified in [kdcdefaults] as global defaults, or within a realm-specific subsection of [realms]. A realm-specific value overrides, does not add to, a generic [kdcdefaults] specification. The search order is

realm-specific subsection of [realms]

[realms]

[realms]
    EXAMPLE.COM = {
         pkinit_anchors = FILE:/usr/local/example.com.crt
    }

generic value in the [kdcdefaults] section

[kdcdefaults]
    pkinit_anchors = DIR:/usr/local/generic_trusted_cas/

pkinit_identity = URI

Specifies the location of the KDC's X.509 identity information. This option is required if pkinit is supported by the KDC. Valid URI types are FILE, DIR, PKCS11, PKCS12, and ENV. See the PKINIT URI Types section for more details.

pkinit_anchors = URI

Specifies the location of trusted anchor (root) certificates which the KDC trusts to sign client certificates. This option is required if pkinit is supported by the KDC. This option can be specified multiple times. Valid URI types are FILE and DIR. See the PKINIT URI Types section for details.

pkinit_pool

Specifies the location of intermediate certificates which can be used by the KDC to complete the trust chain between a client's certificate and a trusted anchor. This option can be specified multiple times. Valid URI types are FILE and DIR. See the PKINIT URI Types section for more details.

pkinit_revoke

Specifies the location of Certificate Revocation List (CRL) information to be used by the KDC when verifying the validity of client certificates. This option can be specified multiple times. The default certificate verification process always checks the available revocation information to see if a certificate has been revoked. If a match is found for the certificate in a CRL, verification fails. If the certificate being verified is not listed in a CRL, or there is no CRL present for its issuing CA, and pkinit_require_crl_checking is false, then verification succeeds. The only valid URI types is DIR. See the PKINIT URI Types section for more details. If pkinit_require_crl_checking is true and there is no CRL information available for the issuing CA, verification fails. pkinit_require_crl_checking should be set to true if the policy is such that up-to-date CRLs must be present for every CA.

pkinit_dh_min_bits

Specifies the minimum number of bits the KDC is willing to accept for a client's Diffie-Hellman key.

pkinit_allow_upn

Specifies that the KDC is willing to accept client certificates with the Microsoft UserPrincipalName (UPN) Subject Alternative Name (SAN). This means the KDC accepts the binding of the UPN in the certificate to the Kerberos principal name.

The default is false.

Without this option, the KDC only accepts certificates with the id-pkinit-san as defined in RFC4556. There is currently no option to disable SAN checking in the KDC.

pkinit_eku_checking

This option specifies what Extended Key Usage (EKU) values the KDC is willing to accept in client certificates. The values recognized in the kdc.conf file are:

kpClientAuth: This is the default value and specifies that client certificates must have the id-pkinit-KPClientAuth EKU as defined in RFC4556.
scLogin: If scLogin is specified, client certificates with the Microsoft Smart Card Login EKU (id-ms-kp-sc-logon) is accepted.

PKINIT URI Types

FILE:file-name[,key-file-name]

This option has context-specific behavior.

pkinit_identity: file-name specifies the name of a PEM-format file containing the user's certificate. If key-file-name is not specified, the user's private key is expected to be in file-name as well. Otherwise, key-file-name is the name of the file containing the private key.
pkinit_anchors pkinit_pool: file-name is assumed to be the name of an OpenSSL-style ca-bundle file. The ca-bundle file should be base-64 encoded.

DIR:directory-name

This option has context-specific behavior.

pkinit_identity: directory-name specifies a directory with files named *.crt and *.key, where the first part of the file name is the same for matching pairs of certificate and private key files. When a file with a name ending with .crt is found, a matching file ending with .key is assumed to contain the private key. If no such file is found, then the certificate in the .crt is not used.
pkinit_anchors pkinit_pool: directory-name is assumed to be an OpenSSL-style hashed CA directory where each CA cert is stored in a file named hash-of-ca-cert.#. This infrastructure is encouraged, but all files in the directory is examined and if they contain certificates (in PEM format), they are used.
pkinit_revoke: directory-name is assumed to be an OpenSSL-style hashed CA directory where each revocation list is stored in a file named hash-of-ca-cert.r#. This infrastructure is encouraged, but all files in the directory is examined and if they contain a revocation list (in PEM format), they are used.

PKCS12:pkcs12-file-name

pkcs12-file-name is the name of a PKCS #12 format file, containing the user's certificate and private key.

PKCS11:[slotid=slot-id][:token=token-label][:certid=cert-id][:certlabel=cert-label]

All keyword/values are optional. PKCS11 modules (for example, opensc-pkcs11.so) must be installed as a crypto provider under libpkcs11(3LIB). slotid= and/or token= can be specified to force the use of a particular smard card reader or token if there is more than one available. certid= and/or certlabel= can be specified to force the selection of a particular certificate on the device. See the pkinit_cert_match configuration option for more ways to select a particular certificate to use for pkinit.

ENV:environment-variable-name

environment-variable-name specifies the name of an environment variable which has been set to a value conforming to one of the previous values. For example, ENV:X509_PROXY, where environment variable X509_PROXY has been set to FILE:/tmp/my_proxy.pem.

Examples

Example 1 Sample `kdc.conf` File

The following is an example of a kdc.conf file:

[kdcdefaults]
   kdc_ports = 88

[realms]
   ATHENA.MIT.EDU = { 
      kadmind_port = 749
      max_life = 10h 0m 0s
      max_renewable_life = 7d 0h 0m 0s
      default_principal_flags = +preauth,+forwardable,-postdateable
      master_key_type = des-cbc-crc
      supported_enctypes = des-cbc-crc:normal
   }

[logging]
   kdc = FILE:/export/logging/kdc.log
   admin_server = FILE:/export/logging/kadmin.log

Files

/etc/krb5/kadm5.acl: List of principals and their kadmin administrative privileges.
/etc/krb5/kadm5.keytab: Keytab for kadmind principals: kadmin/fqdn, changepw/fqdn, and kadmin/changepw.
/var/krb5/principal: Kerberos principal database.
/var/krb5/principal.ulog: The update log file for incremental propagation.
/var/krb5/kadm5.dict: Dictionary of strings explicitly disallowed as passwords.
/var/krb5/kdc.log: KDC logging file.
/var/krb5/kadmin.log: Kerberos administration server logging file.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Availability	SUNWkdcu
Interface Stability	See below.

All of the keywords, except for the PKINIT keywords are Committed. The PKINIT keywords are Volatile.