kdc.conf¶

The kdc.conf file supplements krb5.conf for programs which are typically only used on a KDC, such as the krb5kdc and kadmind daemons and the kdb5_util 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, LOCALSTATEDIR/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 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 daemons perform logging

[kdcdefaults]¶

Some relations in the [kdcdefaults] section specify default values for realm variables, to be used if the [realms] subsection does not contain a relation for the tag. See the [realms] section for the definitions of these relations.

host_based_services
kdc_listen
kdc_ports
kdc_tcp_listen
kdc_tcp_ports
no_host_referral
restrict_anonymous_to_tgt

The following [kdcdefaults] variables have no per-realm equivalent:

kdc_max_dgram_reply_size: Specifies the maximum packet size that can be sent over UDP. The default value is 4096 bytes.
kdc_tcp_listen_backlog: (Integer.) Set the size of the listen queue length for the KDC daemon. The value may be limited by OS settings. The default value is 5.
spake_preauth_kdc_challenge: (String.) Specifies the group for a SPAKE optimistic challenge. See the spake_preauth_groups variable in [libdefaults] for possible values. The default is not to issue an optimistic challenge. (New in release 1.17.)

[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. The following example shows how to define one parameter for the ATHENA.MIT.EDU realm:

[realms]
    ATHENA.MIT.EDU = {
        max_renewable_life = 7d 0h 0m 0s
    }

The following tags may be specified in a [realms] subsection:

acl_file

(String.) Location of the access control list file that kadmind uses to determine which principals are allowed which permissions on the Kerberos database. To operate without an ACL file, set this relation to the empty string with acl_file = "". The default value is LOCALSTATEDIR/krb5kdc/kadm5.acl. For more information on Kerberos ACL file see kadm5.acl.

database_module

(String.) This relation indicates the name of the configuration section under [dbmodules] for database-specific parameters used by the loadable database library. The default value is the realm name. If this configuration section does not exist, default values will be used for all database parameters.

database_name

(String, deprecated.) This relation specifies the location of the Kerberos database for this realm, if the DB2 module is being used and the [dbmodules] configuration section does not specify a database name. The default value is LOCALSTATEDIR/krb5kdc/principal.

default_principal_expiration

(Absolute time 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 disabled. 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 KDC to issue user-to-user service tickets 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 tickets.
no-auth-data-required: Enabling this flag prevents PAC or AD-SIGNEDPATH 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. In release 1.17 and later, user-to-user service tickets are still allowed if the dup-skey flag is set.
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. The file should contain one string per line, with no additional whitespace. If none is specified or if there is no policy assigned to the principal, no dictionary checks of passwords will be performed.

disable_pac

(Boolean value.) If true, the KDC will not issue PACs for this realm, and S4U2Self and S4U2Proxy operations will be disabled. The default is false, which will permit the KDC to issue PACs. New in release 1.20.

encrypted_challenge_indicator

(String.) Specifies the authentication indicator value that the KDC asserts into tickets obtained using FAST encrypted challenge pre-authentication. New in 1.16.

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_ulogsize

(Integer.) Specifies the maximum number of log entries to be retained for incremental propagation. The default value is 1000. Prior to release 1.11, the maximum value was 2500. New in release 1.19.

iprop_master_ulogsize

The name for iprop_ulogsize prior to release 1.19. Its value is used as a fallback if iprop_ulogsize is not specified.

iprop_replica_poll

(Delta time string.) Specifies how often the replica KDC polls for new updates from the primary. The default value is 2m (that is, two minutes). New in release 1.17.

iprop_slave_poll

(Delta time string.) The name for iprop_replica_poll prior to release 1.17. Its value is used as a fallback if iprop_replica_poll is not specified.

iprop_listen

(Whitespace- or comma-separated list.) Specifies the iprop RPC listening addresses and/or ports for the kadmind daemon. Each entry may be an interface address, a port number, or an address and port number separated by a colon. If the address contains colons, enclose it in square brackets. If no address is specified, the wildcard address is used. If kadmind fails to bind to any of the specified addresses, it will fail to start. The default (when iprop_enable is true) is to bind to the wildcard address at the port specified in iprop_port. New in release 1.15.

iprop_port

(Port number.) Specifies the port number to be used for incremental propagation. When iprop_enable is true, this relation is required in the replica KDC configuration file, and this relation or iprop_listen is required in the primary configuration file, as there is no default port number. Port numbers specified in iprop_listen entries will override this port number for the kadmind daemon.

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 replica KDCs only. The default value is 5 minutes (5m). New in release 1.11.

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_listen

(Whitespace- or comma-separated list.) Specifies the kadmin RPC listening addresses and/or ports for the kadmind daemon. Each entry may be an interface address, a port number, an address and port number separated by a colon, or a UNIX domain socket pathname. If the address contains colons, enclose it in square brackets. If no address is specified, the wildcard address is used. To disable listening for kadmin RPC connections, set this relation to the empty string with kadmind_listen = "". If kadmind fails to bind to any of the specified addresses, it will fail to start. The default is to bind to the wildcard address at the port specified in kadmind_port, or the standard kadmin port (749). New in release 1.15.

kadmind_port

(Port number.) Specifies the port on which the kadmind daemon is to listen for this realm. Port numbers specified in kadmind_listen entries will override this port number. 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 LOCALSTATEDIR/krb5kdc/.k5.REALM, where REALM is the Kerberos realm.

kdc_listen

(Whitespace- or comma-separated list.) Specifies the listening addresses and/or ports for the krb5kdc daemon. Each entry may be an interface address, a port number, an address and port number separated by a colon, or a UNIX domain socket pathname. If the address contains colons, enclose it in square brackets. If no address is specified, the wildcard address is used. If no port is specified, the standard port (88) is used. To disable listening on UDP, set this relation to the empty string with kdc_listen = "". If the KDC daemon fails to bind to any of the specified addresses, it will fail to start. The default is to bind to the wildcard address on the standard port. New in release 1.15.

kdc_ports

(Whitespace- or comma-separated list, deprecated.) Prior to release 1.15, this relation lists the ports for the krb5kdc daemon to listen on for UDP requests. In release 1.15 and later, it has the same meaning as kdc_listen if that relation is not defined.

kdc_tcp_listen

(Whitespace- or comma-separated list.) Specifies the TCP listening addresses and/or ports for the krb5kdc daemon. The syntax is identical to that of kdc_listen. To disable listening on TCP, set this relation to the empty string with kdc_tcp_listen = "". The default is to bind to the same addresses and ports as for UDP. New in release 1.15.

kdc_tcp_ports

kpasswd_listen

(Comma-separated list.) Specifies the kpasswd listening addresses and/or ports for the kadmind daemon. Each entry may be an interface address, a port number, an address and port number separated by a colon, or a UNIX domain socket pathname. If the address contains colons, enclose it in square brackets. If no address is specified, the wildcard address is used. To disable listening for kpasswd requests, set this relation to the empty string with kpasswd_listen = "". If kadmind fails to bind to any of the specified addresses, it will fail to start. The default is to bind to the wildcard address at the port specified in kpasswd_port, or the standard kpasswd port (464). New in release 1.15.

kpasswd_port

(Port number.) Specifies the port on which the kadmind daemon is to listen for password change requests for this realm. Port numbers specified in kpasswd_listen entries will override this port number. The assigned port for password change requests is 464, which is used by default.

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 types.

max_life

(Time 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

(Time 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.

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 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. New in release 1.9.

spake_preauth_indicator

(String.) Specifies an authentication indicator value that the KDC asserts into tickets obtained using SPAKE pre-authentication. The default is not to add any indicators. This option may be specified multiple times. New in release 1.17.

supported_enctypes

(List of key:salt strings.) Specifies the default key/salt combinations of principals for this realm. Any principals created through kadmin 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. For lists of possible values, see Keysalt lists.

[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_kdc_sasl_authcid
ldap_kdc_sasl_authzid
ldap_kdc_sasl_mech
ldap_kdc_sasl_realm
ldap_kadmind_dn
ldap_kadmind_sasl_authcid
ldap_kadmind_sasl_authzid
ldap_kadmind_sasl_mech
ldap_kadmind_sasl_realm
ldap_service_password_file
ldap_conns_per_server

[dbmodules]¶

The [dbmodules] section contains parameters used by the KDC database library and database modules. Each tag in the [dbmodules] section is the name of a Kerberos realm or a section name specified by a realm’s database_module parameter. The following example shows how to define one database parameter for the ATHENA.MIT.EDU realm:

[dbmodules]
    ATHENA.MIT.EDU = {
        disable_last_success = true
    }

The following tags may be specified in a [dbmodules] subsection:

database_name: This DB2-specific tag indicates the location of the database in the filesystem. The default is LOCALSTATEDIR/krb5kdc/principal.
db_library: This tag indicates the name of the loadable database module. The value should be db2 for the DB2 module, klmdb for the LMDB module, or 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 preauthentication. Setting this flag may improve performance. (Principal entries which do not require preauthentication never update the “Last successful authentication” field.). First introduced in release 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 introduced in release 1.9.
ldap_conns_per_server: This LDAP-specific tag indicates the number of connections to be maintained per LDAP server.
ldap_kdc_dn and ldap_kadmind_dn: These LDAP-specific tags indicate the default DN for binding to the LDAP server. The krb5kdc daemon uses ldap_kdc_dn, while the kadmind daemon and other administrative programs use ldap_kadmind_dn. The kadmind DN must have the rights to read and write the Kerberos data in the LDAP database. The KDC DN must have the same rights, unless disable_lockout and disable_last_success are true, in which case it only needs to have rights to read the Kerberos data. These tags are ignored if a SASL mechanism is set with ldap_kdc_sasl_mech or ldap_kadmind_sasl_mech.
ldap_kdc_sasl_mech and ldap_kadmind_sasl_mech: These LDAP-specific tags specify the SASL mechanism (such as EXTERNAL) to use when binding to the LDAP server. New in release 1.13.
ldap_kdc_sasl_authcid and ldap_kadmind_sasl_authcid: These LDAP-specific tags specify the SASL authentication identity to use when binding to the LDAP server. Not all SASL mechanisms require an authentication identity. If the SASL mechanism requires a secret (such as the password for DIGEST-MD5), these tags also determine the name within the ldap_service_password_file where the secret is stashed. New in release 1.13.
ldap_kdc_sasl_authzid and ldap_kadmind_sasl_authzid: These LDAP-specific tags specify the SASL authorization identity to use when binding to the LDAP server. In most circumstances they do not need to be specified. New in release 1.13.
ldap_kdc_sasl_realm and ldap_kadmind_sasl_realm: These LDAP-specific tags specify the SASL realm to use when binding to the LDAP server. In most circumstances they do not need to be set. New in release 1.13.
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_kdc_dn and ldap_kadmind_dn objects, or for the ldap_kdc_sasl_authcid or ldap_kadmind_sasl_authcid names for SASL authentication. This file must be kept secure.
mapsize: This LMDB-specific tag indicates the maximum size of the two database environments in megabytes. The default value is 128. Increase this value to address “Environment mapsize limit reached” errors. New in release 1.17.
max_readers: This LMDB-specific tag indicates the maximum number of concurrent reading processes for the databases. The default value is 128. New in release 1.17.
nosync: This LMDB-specific tag can be set to improve the throughput of kadmind and other administrative agents, at the expense of durability (recent database changes may not survive a power outage or other sudden reboot). It does not affect the throughput of the KDC. The default value is false. New in release 1.17.
unlockiter: If set to true, this DB2-specific tag causes iteration operations to release the database lock while processing each principal. Setting this flag to true can prevent extended blocking of KDC or kadmin operations when dumps of large databases are in progress. First introduced in release 1.13.

The following tag may be specified directly in the [dbmodules] section to control where database modules are loaded from:

db_module_dir: This tag controls where the plugin system looks for database modules. The value should be an absolute path.

[logging]¶

The [logging] section indicates how krb5kdc and kadmind perform logging. It may contain the following relations:

admin_server: Specifies how kadmind performs logging.
kdc: Specifies how krb5kdc performs logging.
default: Specifies how either daemon performs logging in the absence of relations specific to the daemon.
debug: (Boolean value.) Specifies whether debugging messages are included in log outputs other than SYSLOG. Debugging messages are always included in the system log output because syslog performs its own priority filtering. The default value is false. New in release 1.15.

Logging specifications may have 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.

For backward compatibility, a severity argument may be specified, and must be specified in order to specify a facility. This argument will be ignored.

The facility argument specifies the facility under which the messages are logged. This may be any of the following facilities 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 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, 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

If no logging specification is given, the default is to use syslog. To disable logging entirely, specify default = DEVICE=/dev/null.

[otp]¶

Each subsection of [otp] is the name of an OTP token type. The tags within the subsection define the configuration required to forward a One Time Password request to a RADIUS server.

For each token type, the following tags may be specified:

server: This is the server to send the RADIUS request to. It can be a hostname with optional port, an ip address with optional port, or a Unix domain socket address. The default is LOCALSTATEDIR/krb5kdc/<name>.socket.
secret: This tag indicates a filename (which may be relative to LOCALSTATEDIR/krb5kdc) containing the secret used to encrypt the RADIUS packets. The secret should appear in the first line of the file by itself; leading and trailing whitespace on the line will be removed. If the value of server is a Unix domain socket address, this tag is optional, and an empty secret will be used if it is not specified. Otherwise, this tag is required.
timeout: An integer which specifies the time in seconds during which the KDC should attempt to contact the RADIUS server. This tag is the total time across all retries and should be less than the time which an OTP value remains valid for. The default is 5 seconds.
retries: This tag specifies the number of retries to make to the RADIUS server. The default is 3 retries (4 tries).
strip_realm: If this tag is true, the principal without the realm will be passed to the RADIUS server. Otherwise, the realm will be included. The default value is true.
indicator: This tag specifies an authentication indicator to be included in the ticket if this token type is used to authenticate. This option may be specified multiple times. (New in release 1.14.)

In the following example, requests are sent to a remote server via UDP:

[otp]
    MyRemoteTokenType = {
        server = radius.mydomain.com:1812
        secret = SEmfiajf42$
        timeout = 15
        retries = 5
        strip_realm = true
    }

An implicit default token type named DEFAULT is defined for when the per-principal configuration does not specify a token type. Its configuration is shown below. You may override this token type to something applicable for your situation:

[otp]
    DEFAULT = {
        strip_realm = false
    }

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-specific value over-rides, does not add to, a generic [kdcdefaults] specification. The search order is:

realm-specific subsection of [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/

For information about the syntax of some of these options, see Specifying PKINIT identity information in krb5.conf.

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 strength of Diffie-Hellman group the KDC is willing to accept for key exchange. Valid values in order of increasing strength are 1024, 2048, P-256, 4096, P-384, and P-521. The default is 2048. (P-256, P-384, and P-521 are new in release 1.22.)

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 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_indicator

Specifies an authentication indicator to include in the ticket if pkinit is used to authenticate. This option may be specified multiple times. (New in release 1.14.)

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 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.

pkinit_require_freshness

Specifies whether to require clients to include a freshness token in PKINIT requests. The default value is false. (New in release 1.17.)

Encryption 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” and “deprecated” are available for compatibility but not recommended for use.

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 (deprecated)
aes256-cts-hmac-sha1-96 aes256-cts aes256-sha1	AES-256 CTS mode with 96-bit SHA-1 HMAC
aes128-cts-hmac-sha1-96 aes128-cts aes128-sha1	AES-128 CTS mode with 96-bit SHA-1 HMAC
aes256-cts-hmac-sha384-192 aes256-sha2	AES-256 CTS mode with 192-bit SHA-384 HMAC
aes128-cts-hmac-sha256-128 aes128-sha2	AES-128 CTS mode with 128-bit SHA-256 HMAC
arcfour-hmac rc4-hmac arcfour-hmac-md5	RC4 with HMAC/MD5 (deprecated)
arcfour-hmac-exp rc4-hmac-exp arcfour-hmac-md5-exp	Exportable RC4 with HMAC/MD5 (weak)
camellia256-cts-cmac camellia256-cts	Camellia-256 CTS mode with CMAC
camellia128-cts-cmac camellia128-cts	Camellia-128 CTS mode with CMAC
des3	The triple DES family: des3-cbc-sha1
aes	The AES family: aes256-cts-hmac-sha1-96, aes128-cts-hmac-sha1-96, aes256-cts-hmac-sha384-192, and aes128-cts-hmac-sha256-128
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 -rc4” would be the default set of encryption types with RC4 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 implementation (krb5-1.3.1 and earlier). Services running versions of krb5 without AES support must not be given keys of these encryption types in the KDC database.

The aes128-sha2 and aes256-sha2 encryption types are new in release 1.15. Services running versions of krb5 without support for these newer encryption types must not be given keys of these encryption types in the KDC database.

Keysalt lists¶

Kerberos keys for users are usually derived from passwords. Kerberos commands and configuration parameters that affect generation of keys take lists of enctype-salttype (“keysalt”) pairs, known as keysalt lists. Each keysalt pair is an enctype name followed by a salttype name, in the format enc:salt. Individual keysalt list members are separated by comma (”,”) characters or space characters. For example:

kadmin -e aes256-cts:normal,aes128-cts:normal

would start up kadmin so that by default it would generate password-derived keys for the aes256-cts and aes128-cts encryption types, using a normal salt.

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
norealm	same as the default, without using realm information
onlyrealm	uses only realm information as the salt
special	generate a random salt

Sample kdc.conf File¶

Here’s an example of a kdc.conf file:

[kdcdefaults]
    kdc_listen = 88
    kdc_tcp_listen = 88
[realms]
    ATHENA.MIT.EDU = {
        kadmind_port = 749
        max_life = 12h 0m 0s
        max_renewable_life = 7d 0h 0m 0s
        master_key_type = aes256-cts-hmac-sha1-96
        supported_enctypes = aes256-cts-hmac-sha1-96:normal aes128-cts-hmac-sha1-96:normal
        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¶

LOCALSTATEDIR/krb5kdc/kdc.conf

MIT Kerberos Documentation