KDC.CONF(5) MIT Kerberos KDC.CONF(5)NAMEkdc.conf - Kerberos V5 KDC configuration file
The kdc.conf file supplements krb5.conf(5) for programs which are typi‐
cally only used on a KDC, such as the krb5kdc(8) and kadmind(8) daemons
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 set‐
ting the environment variable KRB5_KDC_PROFILE.
Please note that you need to restart the KDC daemon for any configura‐
tion 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 settings │
├──────────────┼────────────────────────────┤
│[dbdefaults] │ Default database settings │
├──────────────┼────────────────────────────┤
│[dbmodules] │ Per-database settings │
├──────────────┼────────────────────────────┤
│[logging] │ Controls how Kerberos dae‐ │
│ │ mons 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.
· host_based_services
· kdc_ports
· kdc_tcp_ports
· no_host_referral
· 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 parame‐
ters for that particular realm.
For each realm, the following tags may be specified:
acl_file
(String.) Location of the access control list file that kad‐
mind(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 Ker‐
beros 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
loadable 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 correspond‐
ing module contains a database_name parameter, that value will
take precedence over this one. The default value is /var/ker‐
beros/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-separated list of flags, with '+' before each flag that
should be enabled and '-' before each flag that should be dis‐
abled. The postdateable, 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 ses‐
sion key for another user, permitting user-to-user
authentication for this principal.
forwardable
Enabling this flag allows the principal to obtain for‐
wardable tickets.
hwauth If this flag is enabled, then the principal is required
to preauthenticate using a hardware device before receiv‐
ing any tickets.
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 creden‐
tials 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 post‐
dateable 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 prin‐
cipal without going through the normal password authenti‐
cation in order to be able to change the password.
renewable
Enabling this flag allows the principal to obtain renew‐
able 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 authentication 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 prin‐
cipal is not marked as host-based by the client.
iprop_enable
(Boolean value.) Specifies whether incremental database propa‐
gation 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 incre‐
mental propagation. This is required in both master and slave
configuration 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 data‐
base_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) dae‐
mon 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-separated list of integers. The default value is 88,750,
which are the assigned Kerberos port and the port historically
used by Kerberos 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 spec‐
ified, the compiled-in default is not to listen for TCP connec‐
tions at all.
If you wish to change this (note that the current implementation
has little protection against denial-of-service attacks), the
standard 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 dis‐
able referral processing altogether.
des_crc_session_supported
(Boolean value). If set to true, the KDC will assume that ser‐
vice principals support des-cbc-crc for session key enctype
negotiation 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_transit 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 com‐
binations 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 arc‐
four-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.
· ldap_kerberos_container_dn
· ldap_kdc_dn
· ldap_kadmind_dn
· ldap_service_password_file
· ldap_servers
· 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 module.
disable_last_success
If set to true, suppresses KDC updates to the "Last successful
authentication" field of principal entries requiring preauthen‐
tication. Setting this flag may improve performance. (Princi‐
pal 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 princi‐
pal entries requiring preauthentication. Setting this flag may
improve performance, but also disables account lockout. First
introduced 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_kadmind_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 sup‐
ported 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 facili‐
ties supported 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 admin‐
istrative 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-specific subsection of [realms]. Also note that a realm-spe‐
cific 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 Specify‐
ing 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
recognized in the kdc.conf file are:
kpClientAuth
This is the default value and specifies that client cer‐
tificates must have the id-pkinit-KPClientAuth EKU as
defined in RFC 4556.
scLogin
If scLogin is specified, client certificates with the Mi‐
crosoft 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
certificate 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 suc‐
ceeds.
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. Encryp‐
tion 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 │ Triple DES cbc mode with │
│des3-hmac-sha1 │ HMAC/sha1 │
│des3-cbc-sha1-kd │ │
├───────────────────────────┼────────────────────────────┤
│des-hmac-sha1 │ DES with HMAC/sha1 (weak) │
├───────────────────────────┼────────────────────────────┤
│aes256-cts-hmac-sha1-96 │ CTS mode with 96-bit SHA-1 │
│aes256-cts AES-256 │ HMAC │
├───────────────────────────┼────────────────────────────┤
│aes128-cts-hmac-sha1-96 │ CTS mode with 96-bit SHA-1 │
│aes128-cts AES-128 │ HMAC │
├───────────────────────────┼────────────────────────────┤
│arcfour-hmac rc4-hmac arc‐ │ RC4 with HMAC/MD5 │
│four-hmac-md5 │ │
└───────────────────────────┴────────────────────────────┘
│arcfour-hmac-exp │ Exportable RC4 with │
│rc4-hmac-exp arc‐ │ HMAC/MD5 (weak) │
│four-hmac-md5-exp │ │
├───────────────────────────┼────────────────────────────┤
│camellia256-cts-cmac │ Camellia-256 CTS mode with │
│camellia256-cts │ CMAC │
├───────────────────────────┼────────────────────────────┤
│camellia128-cts-cmac │ Camellia-128 CTS mode with │
│camellia128-cts │ 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: arc‐ │
│ │ four-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 fami‐
lies 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 opera‐
tions, 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 some‐
thing called a salt. The supported salt types are as follows:
┌──────────┬────────────────────────────┐
│normal │ default for Kerberos Ver‐ │
│ │ sion 5 │
├──────────┼────────────────────────────┤
│v4 │ the only type used by Ker‐ │
│ │ beros Version 4 (no salt) │
├──────────┼────────────────────────────┤
│norealm │ same as the default, with‐ │
│ │ out using realm informa‐ │
│ │ tion │
├──────────┼────────────────────────────┤
│onlyrealm │ uses only realm informa‐ │
│ │ tion 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 ALSOkrb5.conf(5), krb5kdc(8), kadm5.acl(5)AUTHOR
MIT
COPYRIGHT
1985-2013, MIT
1.11.3KDC.CONF(5)
