KDC.CONF(5) MIT Kerberos KDC.CONF(5)
NAME
kdc.conf - Kerberos V5 KDC configuration file
The kdc.conf file supplements krb5.conf(5) for programs which are typically only used on a KDC, such as the krb5kdc(8) and kadmind(8) dae-
mons and the kdb5_util(8) program. Relations documented here may also be specified in krb5.conf; for the KDC programs mentioned, krb5.conf
and kdc.conf will be merged into a single configuration profile.
Normally, the kdc.conf file is found in the KDC state directory, /var/kerberos/krb5kdc. You can override the default location by setting
the environment variable KRB5_KDC_PROFILE.
Please note that you need to restart the KDC daemon for any configuration changes to take effect.
STRUCTURE
The kdc.conf file is set up in the same format as the krb5.conf(5) file.
SECTIONS
The kdc.conf file may contain the following sections:
+--------------+---------------------------------------------------+
|[kdcdefaults] | Default values for KDC behavior |
+--------------+---------------------------------------------------+
|[realms] | Realm-specific database configuration and set- |
| | tings |
+--------------+---------------------------------------------------+
|[dbdefaults] | Default database settings |
+--------------+---------------------------------------------------+
|[dbmodules] | Per-database settings |
+--------------+---------------------------------------------------+
|[logging] | Controls how Kerberos daemons perform logging |
+--------------+---------------------------------------------------+
[kdcdefaults]
With one exception, relations in the [kdcdefaults] section specify default values for realm variables, to be used if the [realms] subsec-
tion does not contain a relation for the tag. See the [realms] section for the definitions of these relations.
o host_based_services
o kdc_ports
o kdc_tcp_ports
o no_host_referral
o restrict_anonymous_to_tgt
kdc_max_dgram_reply_size
Specifies the maximum packet size that can be sent over UDP. The default value is 4096 bytes.
[realms]
Each tag in the [realms] section is the name of a Kerberos realm. The value of the tag is a subsection where the relations define KDC
parameters for that particular realm.
For each realm, the following tags may be specified:
acl_file
(String.) Location of the access control list file that kadmind(8) uses to determine which principals are allowed which permissions
on the Kerberos database. The default value is /var/kerberos/krb5kdc/kadm5.acl. For more information on Kerberos ACL file see
kadm5.acl(5).
database_module
This relation indicates the name of the configuration section under [dbmodules] for database specific parameters used by the load-
able database library.
database_name
(String.) This string specifies the location of the Kerberos database for this realm, if the DB2 back-end is being used. If a
database_module is specified for the realm and the corresponding module contains a database_name parameter, that value will take
precedence over this one. The default value is /var/kerberos/krb5kdc/principal.
default_principal_expiration
(abstime string.) Specifies the default expiration date of principals created in this realm. The default value is 0, which means
no expiration date.
default_principal_flags
(Flag string.) Specifies the default attributes of principals created in this realm. The format for this string is a comma-sepa-
rated list of flags, with '+' before each flag that should be enabled and '-' before each flag that should be disabled. The post-
dateable, forwardable, tgt-based, renewable, proxiable, dup-skey, allow-tickets, and service flags default to enabled.
There are a number of possible flags:
allow-tickets
Enabling this flag means that the KDC will issue tickets for this principal. Disabling this flag essentially deactivates the
principal within this realm.
dup-skey
Enabling this flag allows the principal to obtain a session key for another user, permitting user-to-user authentication for
this principal.
forwardable
Enabling this flag allows the principal to obtain forwardable tickets.
hwauth If this flag is enabled, then the principal is required to preauthenticate using a hardware device before receiving any tick-
ets.
no-auth-data-required
Enabling this flag prevents PAC data from being added to service tickets for the principal.
ok-as-delegate
If this flag is enabled, it hints the client that credentials can and should be delegated when authenticating to the service.
ok-to-auth-as-delegate
Enabling this flag allows the principal to use S4USelf tickets.
postdateable
Enabling this flag allows the principal to obtain postdateable tickets.
preauth
If this flag is enabled on a client principal, then that principal is required to preauthenticate to the KDC before receiving
any tickets. On a service principal, enabling this flag means that service tickets for this principal will only be issued to
clients with a TGT that has the preauthenticated bit set.
proxiable
Enabling this flag allows the principal to obtain proxy tickets.
pwchange
Enabling this flag forces a password change for this principal.
pwservice
If this flag is enabled, it marks this principal as a password change service. This should only be used in special cases,
for example, if a user's password has expired, then the user has to get tickets for that principal without going through the
normal password authentication in order to be able to change the password.
renewable
Enabling this flag allows the principal to obtain renewable tickets.
service
Enabling this flag allows the the KDC to issue service tickets for this principal.
tgt-based
Enabling this flag allows a principal to obtain tickets based on a ticket-granting-ticket, rather than repeating the authen-
tication process that was used to obtain the TGT.
dict_file
(String.) Location of the dictionary file containing strings that are not allowed as passwords. If none is specified or if there
is no policy assigned to the principal, no dictionary checks of passwords will be performed.
host_based_services
(Whitespace- or comma-separated list.) Lists services which will get host-based referral processing even if the server principal is
not marked as host-based by the client.
iprop_enable
(Boolean value.) Specifies whether incremental database propagation is enabled. The default value is false.
iprop_master_ulogsize
(Integer.) Specifies the maximum number of log entries to be retained for incremental propagation. The maximum value is 2500; the
default value is 1000.
iprop_slave_poll
(Delta time string.) Specifies how often the slave KDC polls for new updates from the master. The default value is 2m (that is,
two minutes).
iprop_port
(Port number.) Specifies the port number to be used for incremental propagation. This is required in both master and slave config-
uration files.
iprop_resync_timeout
(Delta time string.) Specifies the amount of time to wait for a full propagation to complete. This is optional in configuration
files, and is used by slave KDCs only. The default value is 5 minutes (5m).
iprop_logfile
(File name.) Specifies where the update log file for the realm database is to be stored. The default is to use the database_name
entry from the realms section of the krb5 config file, with .ulog appended. (NOTE: If database_name isn't specified in the realms
section, perhaps because the LDAP database back end is being used, or the file name is specified in the [dbmodules] section, then
the hard-coded default for database_name is used. Determination of the iprop_logfile default value will not use values from the
[dbmodules] section.)
kadmind_port
(Port number.) Specifies the port on which the kadmind(8) daemon is to listen for this realm. The assigned port for kadmind is
749, which is used by default.
key_stash_file
(String.) Specifies the location where the master key has been stored (via kdb5_util stash). The default is /var/ker-
beros/krb5kdc/.k5.REALM, where REALM is the Kerberos realm.
kdc_ports
(Whitespace- or comma-separated list.) Lists the ports on which the Kerberos server should listen for UDP requests, as a comma-sep-
arated list of integers. The default value is 88,750, which are the assigned Kerberos port and the port historically used by Ker-
beros V4.
kdc_tcp_ports
(Whitespace- or comma-separated list.) Lists the ports on which the Kerberos server should listen for TCP connections, as a
comma-separated list of integers. If this relation is not specified, the compiled-in default is not to listen for TCP connections
at all.
If you wish to change this (note that the current implementation has little protection against denial-of-service attacks), the stan-
dard port number assigned for Kerberos TCP traffic is port 88.
master_key_name
(String.) Specifies the name of the principal associated with the master key. The default is K/M.
master_key_type
(Key type string.) Specifies the master key's key type. The default value for this is aes256-cts-hmac-sha1-96. For a list of all
possible values, see Encryption and salt types.
max_life
(duration string.) Specifies the maximum time period for which a ticket may be valid in this realm. The default value is 24 hours.
max_renewable_life
(duration string.) Specifies the maximum time period during which a valid ticket may be renewed in this realm. The default value
is 0.
no_host_referral
(Whitespace- or comma-separated list.) Lists services to block from getting host-based referral processing, even if the client
marks the server principal as host-based or the service is also listed in host_based_services. no_host_referral = * will disable
referral processing altogether.
des_crc_session_supported
(Boolean value). If set to true, the KDC will assume that service principals support des-cbc-crc for session key enctype negotia-
tion purposes. If allow_weak_crypto in libdefaults is false, or if des-cbc-crc is not a permitted enctype, then this variable has
no effect. Defaults to true.
reject_bad_transit
(Boolean value.) If set to true, the KDC will check the list of transited realms for cross-realm tickets against the transit path
computed from the realm names and the capaths section of its krb5.conf(5) file; if the path in the ticket to be issued contains any
realms not in the computed path, the ticket will not be issued, and an error will be returned to the client instead. If this value
is set to false, such tickets will be issued anyways, and it will be left up to the application server to validate the realm transit
path.
If the disable-transited-check flag is set in the incoming request, this check is not performed at all. Having the reject_bad_tran-
sit option will cause such ticket requests to be rejected always.
This transit path checking and config file option currently apply only to TGS requests.
The default value is true.
restrict_anonymous_to_tgt
(Boolean value.) If set to true, the KDC will reject ticket requests from anonymous principals to service principals other than the
realm's ticket-granting service. This option allows anonymous PKINIT to be enabled for use as FAST armor tickets without allowing
anonymous authentication to services. The default value is false.
supported_enctypes
(List of key:salt strings.) Specifies the default key/salt combinations of principals for this realm. Any principals created
through kadmin(1) will have keys of these types. The default value for this tag is aes256-cts-hmac-sha1-96:normal
aes128-cts-hmac-sha1-96:normal des3-cbc-sha1:normal arcfour-hmac-md5:normal. For lists of possible values, see Encryption and salt
types.
[dbdefaults]
The [dbdefaults] section specifies default values for some database parameters, to be used if the [dbmodules] subsection does not contain a
relation for the tag. See the [dbmodules] section for the definitions of these relations.
o ldap_kerberos_container_dn
o ldap_kdc_dn
o ldap_kadmind_dn
o ldap_service_password_file
o ldap_servers
o ldap_conns_per_server
[dbmodules]
The [dbmodules] section contains parameters used by the KDC database library and database modules.
The following tag may be specified in the [dbmodules] section:
db_module_dir
This tag controls where the plugin system looks for modules. The value should be an absolute path.
Other tags in the [dbmodules] section name a configuration subsection for parameters which can be referred to by a realm's database_module
parameter. The following tags may be specified in the subsection:
database_name
This DB2-specific tag indicates the location of the database in the filesystem. The default is /var/kerberos/krb5kdc/principal.
db_library
This tag indicates the name of the loadable database module. The value should be db2 for the DB2 module and kldap for the LDAP mod-
ule.
disable_last_success
If set to true, suppresses KDC updates to the "Last successful authentication" field of principal entries requiring preauthentica-
tion. Setting this flag may improve performance. (Principal entries which do not require preauthentication never update the "Last
successful authentication" field.). First introduced in version 1.9.
disable_lockout
If set to true, suppresses KDC updates to the "Last failed authentication" and "Failed password attempts" fields of principal
entries requiring preauthentication. Setting this flag may improve performance, but also disables account lockout. First intro-
duced in version 1.9.
ldap_conns_per_server
This LDAP-specific tag indicates the number of connections to be maintained per LDAP server.
ldap_kadmind_dn
This LDAP-specific tag indicates the default bind DN for the kadmind(8) daemon. kadmind does a login to the directory as this
object. This object should have the rights to read and write the Kerberos data in the LDAP database.
ldap_kdc_dn
This LDAP-specific tag indicates the default bind DN for the krb5kdc(8) daemon. The KDC does a login to the directory as this
object. This object should have the rights to read the Kerberos data in the LDAP database, and to write data unless disable_lockout
and disable_last_success are true.
ldap_kerberos_container_dn
This LDAP-specific tag indicates the DN of the container object where the realm objects will be located.
ldap_servers
This LDAP-specific tag indicates the list of LDAP servers that the Kerberos servers can connect to. The list of LDAP servers is
whitespace-separated. The LDAP server is specified by a LDAP URI. It is recommended to use ldapi: or ldaps: URLs to connect to the
LDAP server.
ldap_service_password_file
This LDAP-specific tag indicates the file containing the stashed passwords (created by kdb5_ldap_util stashsrvpw) for the ldap_kad-
mind_dn and ldap_kdc_dn objects. This file must be kept secure.
[logging]
The [logging] section indicates how krb5kdc(8) and kadmind(8) perform logging. The keys in this section are daemon names, which may be one
of:
admin_server
Specifies how kadmind(8) performs logging.
kdc Specifies how krb5kdc(8) performs logging.
default
Specifies how either daemon performs logging in the absence of relations specific to the daemon.
Values are of the following forms:
FILE=filename or FILE:filename
This value causes the daemon's logging messages to go to the filename. If the = form is used, the file is overwritten. If the :
form is used, the file is appended to.
STDERR This value causes the daemon's logging messages to go to its standard error stream.
CONSOLE
This value causes the daemon's logging messages to go to the console, if the system supports it.
DEVICE=<devicename>
This causes the daemon's logging messages to go to the specified device.
SYSLOG[:severity[:facility]]
This causes the daemon's logging messages to go to the system log.
The severity argument specifies the default severity of system log messages. This may be any of the following severities supported
by the syslog(3) call, minus the LOG_ prefix: EMERG, ALERT, CRIT, ERR, WARNING, NOTICE, INFO, and DEBUG.
The facility argument specifies the facility under which the messages are logged. This may be any of the following facilities sup-
ported by the syslog(3) call minus the LOG_ prefix: KERN, USER, MAIL, DAEMON, AUTH, LPR, NEWS, UUCP, CRON, and LOCAL0 through
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 will go to the console and to the system log under the facility LOG_DAEMON with
default severity of LOG_INFO; and the logging messages from the administrative server will be appended to the file /var/adm/kadmin.log and
sent to the device /dev/tty04.
[logging]
kdc = CONSOLE
kdc = SYSLOG:INFO:DAEMON
admin_server = FILE:/var/adm/kadmin.log
admin_server = DEVICE=/dev/tty04
PKINIT OPTIONS
NOTE:
The following are pkinit-specific options. These values may be specified in [kdcdefaults] as global defaults, or within a realm-spe-
cific subsection of [realms]. Also note that a realm-specific value over-rides, does not add to, a generic [kdcdefaults] specification.
The search order is:
1. realm-specific subsection of [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/
For information about the syntax of some of these options, see Specifying PKINIT identity information in krb5.conf(5).
pkinit_anchors
Specifies the location of trusted anchor (root) certificates which the KDC trusts to sign client certificates. This option is
required if pkinit is to be supported by the KDC. This option may be specified multiple times.
pkinit_dh_min_bits
Specifies the minimum number of bits the KDC is willing to accept for a client's Diffie-Hellman key. The default is 2048.
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 value is
false.
Without this option, the KDC will only accept certificates with the id-pkinit-san as defined in RFC 4556. 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 recog-
nized 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 RFC
4556.
scLogin
If scLogin is specified, client certificates with the Microsoft Smart Card Login EKU (id-ms-kp-sc-logon) will be accepted.
none If none is specified, then client certificates will not be checked to verify they have an acceptable EKU. The use of this
option is not recommended.
pkinit_identity
Specifies the location of the KDC's X.509 identity information. This option is required if pkinit is to be supported by the KDC.
pkinit_kdc_ocsp
Specifies the location of the KDC's OCSP.
pkinit_mapping_file
Specifies the name of the ACL pkinit mapping file. This file maps principals to the certificates that they can use.
pkinit_pool
Specifies the location of intermediate certificates which may be used by the KDC to complete the trust chain between a client's cer-
tificate and a trusted anchor. This option may be specified multiple times.
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 may be specified multiple times.
pkinit_require_crl_checking
The default certificate verification process will always check 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.
However, if pkinit_require_crl_checking is true and there is no CRL information available for the issuing CA, then 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.
ENCRYPTION AND SALT TYPES
Any tag in the configuration files which requires a list of encryption types can be set to some combination of the following strings.
Encryption types marked as "weak" are available for compatibility but not recommended for use.
+--------------------------------------------------+---------------------------------------------------+
|des-cbc-crc | DES cbc mode with CRC-32 (weak) |
+--------------------------------------------------+---------------------------------------------------+
|des-cbc-md4 | DES cbc mode with RSA-MD4 (weak) |
+--------------------------------------------------+---------------------------------------------------+
|des-cbc-md5 | DES cbc mode with RSA-MD5 (weak) |
+--------------------------------------------------+---------------------------------------------------+
|des-cbc-raw | DES cbc mode raw (weak) |
+--------------------------------------------------+---------------------------------------------------+
|des3-cbc-raw | Triple DES cbc mode raw (weak) |
+--------------------------------------------------+---------------------------------------------------+
|des3-cbc-sha1 des3-hmac-sha1 des3-cbc-sha1-kd | Triple DES cbc mode with HMAC/sha1 |
+--------------------------------------------------+---------------------------------------------------+
|des-hmac-sha1 | DES with HMAC/sha1 (weak) |
+--------------------------------------------------+---------------------------------------------------+
|aes256-cts-hmac-sha1-96 aes256-cts AES-256 | CTS mode with 96-bit SHA-1 HMAC |
+--------------------------------------------------+---------------------------------------------------+
|aes128-cts-hmac-sha1-96 aes128-cts AES-128 | CTS mode with 96-bit SHA-1 HMAC |
+--------------------------------------------------+---------------------------------------------------+
|arcfour-hmac rc4-hmac arcfour-hmac-md5 | RC4 with HMAC/MD5 |
+--------------------------------------------------+---------------------------------------------------+
|arcfour-hmac-exp rc4-hmac-exp arc- | Exportable RC4 with HMAC/MD5 (weak) |
|four-hmac-md5-exp | |
+--------------------------------------------------+---------------------------------------------------+
|camellia256-cts-cmac camellia256-cts | Camellia-256 CTS mode with CMAC |
+--------------------------------------------------+---------------------------------------------------+
|camellia128-cts-cmac camellia128-cts | Camellia-128 CTS mode with CMAC |
+--------------------------------------------------+---------------------------------------------------+
|des | The DES family: des-cbc-crc, des-cbc-md5, and |
| | des-cbc-md4 (weak) |
+--------------------------------------------------+---------------------------------------------------+
|des3 | The triple DES family: des3-cbc-sha1 |
+--------------------------------------------------+---------------------------------------------------+
|aes | The AES family: aes256-cts-hmac-sha1-96 and |
| | aes128-cts-hmac-sha1-96 |
+--------------------------------------------------+---------------------------------------------------+
|rc4 | The RC4 family: arcfour-hmac |
+--------------------------------------------------+---------------------------------------------------+
|camellia | The Camellia family: camellia256-cts-cmac and |
| | camellia128-cts-cmac |
+--------------------------------------------------+---------------------------------------------------+
The string DEFAULT can be used to refer to the default set of types for the variable in question. Types or families can be removed from
the current list by prefixing them with a minus sign ("-"). Types or families can be prefixed with a plus sign ("+") for symmetry; it has
the same meaning as just listing the type or family. For example, "DEFAULT -des" would be the default set of encryption types with DES
types removed, and "des3 DEFAULT" would be the default set of encryption types with triple DES types moved to the front.
While aes128-cts and aes256-cts are supported for all Kerberos operations, they are not supported by very old versions of our GSSAPI imple-
mentation (krb5-1.3.1 and earlier). Services running versions of krb5 without AES support must not be given AES keys in the KDC database.
Kerberos keys for users are usually derived from passwords. To ensure that people who happen to pick the same password do not have the
same key, Kerberos 5 incorporates more information into the key using something called a salt. The supported salt types are as follows:
+----------+---------------------------------------------------+
|normal | default for Kerberos Version 5 |
+----------+---------------------------------------------------+
|v4 | the only type used by Kerberos Version 4 (no |
| | salt) |
+----------+---------------------------------------------------+
|norealm | same as the default, without using realm informa- |
| | tion |
+----------+---------------------------------------------------+
|onlyrealm | uses only realm information as the salt |
+----------+---------------------------------------------------+
|afs3 | AFS version 3, only used for compatibility with |
| | Kerberos 4 in AFS |
+----------+---------------------------------------------------+
|special | generate a random salt |
+----------+---------------------------------------------------+
SAMPLE KDC.CONF FILE
Here's an example of a kdc.conf file:
[kdcdefaults]
kdc_ports = 88
[realms]
ATHENA.MIT.EDU = {
kadmind_port = 749
max_life = 12h 0m 0s
max_renewable_life = 7d 0h 0m 0s
master_key_type = des3-hmac-sha1
supported_enctypes = des3-hmac-sha1:normal des-cbc-crc:normal des-cbc-crc:v4
database_module = openldap_ldapconf
}
[logging]
kdc = FILE:/usr/local/var/krb5kdc/kdc.log
admin_server = FILE:/usr/local/var/krb5kdc/kadmin.log
[dbdefaults]
ldap_kerberos_container_dn = cn=krbcontainer,dc=mit,dc=edu
[dbmodules]
openldap_ldapconf = {
db_library = kldap
disable_last_success = true
ldap_kdc_dn = "cn=krbadmin,dc=mit,dc=edu"
# this object needs to have read rights on
# the realm container and principal subtrees
ldap_kadmind_dn = "cn=krbadmin,dc=mit,dc=edu"
# this object needs to have read and write rights on
# the realm container and principal subtrees
ldap_service_password_file = /etc/kerberos/service.keyfile
ldap_servers = ldaps://kerberos.mit.edu
ldap_conns_per_server = 5
}
FILES
/var/kerberos/krb5kdc/kdc.conf
SEE ALSO
krb5.conf(5), krb5kdc(8), kadm5.acl(5)
AUTHOR
MIT
COPYRIGHT
1985-2013, MIT
1.11.3 KDC.CONF(5)