KDC.CONF(4) File Formats and Configurations 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


or

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 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


or

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

1. realm-specific subsection of [realms]

[realms]

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


2. 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 |
+--------------------+-----------------+
|Interface Stability | See below. |
+--------------------+-----------------+


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

SEE ALSO


kpasswd(1), kadmind(1M), kadmin.local(1M), kdb5_util(1M), kpropd(1M),
libpkcs11(3LIB), syslog(3C), kadm5.acl(4), krb5.conf(4), attributes(5),
kerberos(5)


October 29, 2015 KDC.CONF(4)