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krb5.conf(4) File Formats krb5.conf(4) NAME krb5.conf - Kerberos configuration file SYNOPSIS /etc/krb5/krb5.conf DESCRIPTION The krb5.conf file contains Kerberos configuration information, includ- ing the locations of KDCs and administration daemons for the Kerberos realms of interest, defaults for the current realm and for Kerberos ap- plications, and mappings of host names onto Kerberos realms. This file must reside on all Kerberos clients. The format of the krb5.conf consists of sections headings in square brackets. Each section may contain zero or more configuration variables (called relations), of the form: relation= relation-value or relation-subsection = { relation= relation-value relation= relation-value } The krb5.conf file may contain any or all of the following seven sec- tions: libdefaults Contains default values used by the Kerberos V5 library. appdefaults Contains subsections for Kerberos V5 applications, where relation- subsection is the name of an application. Each subsection describes application-specific defaults. realms Contains subsections for Kerberos realms, where relation-subsection is the name of a realm. Each subsection contains relations that de- fine the properties for that particular realm. domain_realm Contains relations which map domain names and subdomains onto Ker- beros realm names. This is used by programs to determine what realm a host should be in, given its fully qualified domain name. logging Contains relations which determine how Kerberos programs are to perform logging. capaths Contains the authentication paths used with direct (nonhierarchi- cal) cross-realm authentication. Entries in this section are used by the client to determine the intermediate realms which may be used in cross-realm authentication. It is also used by the end-ser- vice when checking the transited field for trusted intermediate realms. kdc For a KDC, may contain the location of the kdc.conf file. [libdefaults] The [libdefaults] section may contain any of the following relations: default_keytab_name Specifies the default keytab name to be used by application servers such as telnetd and rlogind. The default is /etc/krb5/krb5.keytab. default_realm Identifies the default Kerberos realm for the client. Set its value to your Kerberos realm. default_tgs_enctypes Identifies the supported list of session key encryption types that should be returned by the KDC. The list may be delimited with com- mas or whitespace. The supported encryption types are des3-cbc- sha1, des-cbc-crc, des-cbc-md5, arcfour-hmac-md5, arcfour-hmac- md5-exp, aes128-cts-hmac-sha1-96, and aes256-cts-hmac-sha1-96. default_tkt_enctypes Identifies the supported list of session key encryption types that should be requested by the client. The format is the same as for default_tkt_enctypes. The supported encryption types are des3-cbc- sha1, des-cbc-crc, des-cbc-md5, arcfour-hmac-md5, arcfour-hmac- md5-exp, aes128-cts-hmac-sha1-96, and aes256-cts-hmac-sha1-96. clockskew Sets the maximum allowable amount of clock skew in seconds that the library will tolerate before assuming that a Kerberos message is invalid. The default value is 300 seconds, or five minutes. forwardable = [true | false] Sets the "forwardable" flag in all tickets. This allows users to transfer their credentials from one host to another without reau- thenticating. This option may also be set in the [appdefaults] or [realms] section (see below) to limit its use in particular appli- cations or just to a specific realm. permitted_enctypes This relation controls the encryption types for session keys per- mitted by server applications that use Kerberos for authentication. In addition, it controls the encryption types of keys added to a keytab by means of the kadmin(1M) ktadd command. The default is: aes256-cts-hmac-sha1-96, aes128-cts-hmac-sha1-96, des3-hmac-sha1, arcfour-hmac-md5, des-cbc-md5, des-cbc-crc. proxiable = [true | false] Sets the "proxiable" flag in all tickets. This allows users to cre- ate a proxy ticket that can be transferred to a kerberized service to allow that service to perform some function on behalf of the original user. This option may also be set in the [appdefaults] or [realms] section (see below) to limit its use in particular appli- cations or just to a specific realm. renew_lifetime =lifetime Requests renewable tickets, with a total lifetime of lifetime. The value for lifetime must be followed immediately by one of the fol- lowing delimiters: s seconds m minutes h hours d days Example: renew_lifetime = 90m Do not mix units. A value of "3h30m" will result in an error. max_lifetime =lifetime Sets the requested maximum lifetime of the ticket. The values for lifetime follow the format described for the renew_lifetime option, above. dns_lookup_kdc Indicates whether DNS SRV records need to be used to locate the KDCs and the other servers for a realm, if they have not already been listed in the [realms] section. Enabling this option does make the machine vulnerable to a certain type of DoS attack if somone spoofs the DNS records and does a redirect to another server. This is, however, no worse than a DoS, since the bogus KDC will be un- able to decode anything sent (excepting the initial ticket request, which has no encrypted data). Also, anything the fake KDC sends out will not be trusted without verification (the local machine will be unaware of the secret key to be used). If dns_lookup_kdc is not specified but dns_fallback is, then that value will be used in- stead. In either case, values (if present) in the [realms] section override DNS. dns_lookup_realm Indicates whether DNS TXT records need to be used to determine the Kerberos realm information and/or the host/domain name-to-realm mapping of a host, if this information is not already present in the krb5.conf file. Enabling this option might make the host vul- nerable to a redirection attack, wherein spoofed DNS replies per- suade a client to authenticate to the wrong realm. In a realm with no cross-realm trusts, this a DoS attack. If dns_lookup_realm is not specified but dns_fallback is, then that value will be used in- stead. In either case, values (if present) in the [libdefaults] and [domain_realm] sections override DNS. dns_fallback Generic flag controlling the use of DNS for retrieval of informa- tion about Kerberos servers and host/domain name-to-realm mapping. If both dns_lookup_kdc and dns_lookup_realm have been specified, this option has no effect. verify_ap_req_nofail [true | false] If true, the local keytab file (/etc/krb5/krb5.keytab) must contain an entry for the local host principal, for example, host/foo.bar.com@FOO.COM. This entry is needed to verify that the TGT requested was issued by the same KDC that issued the key for the host principal. If undefined, the behavior is as if this option were set to true. Setting this value to false leaves the system vulnerable to DNS spoofing attacks. This parameter may be in the [realms] section to set it on a per-realm basis, or it may be in the [libdefaults] section to make it a network-wide setting for all realms. [appdefaults] This section contains subsections for Kerberos V5 applications, where relation-subsection is the name of an application. Each subsection con- tains relations that define the default behaviors for that application. The following relations may be found in the [appdefaults] section, though not all relations are recognized by all kerberized applications. Some are specific to particular applications. autologin = [true | false] Forces the application to attempt automatic login by presenting Kerberos credentials. This is only valid for the telnet applica- tion. encrypt = [true | false] Forces applications to use encryption by default (after authentica- tion) to protect the privacy of the sessions. This is valid for the following applications: rlogin, rsh, rcp, rdist, and telnet. forward = [true | false] Forces applications to forward the user'ss credentials (after au- thentication) to the remote server. This is valid for the following applications: rlogin, rsh, rcp, rdist, and telnet. forwardable = [true | false] See the description in the [libdefaults] section above. This is used by any application that creates a ticket granting ticket and also by applications that can forward tickets to a remote server. proxiable = [true | false] See the description in the [libdefaults] section above. This is used by any application that creates a ticket granting ticket. renewable = [true | false] Creates a TGT that can be renewed (prior to the ticket expiration time). This is used by any application that creates a ticket grant- ing ticket. no_addresses = [true | false] Creates tickets with no address bindings. This is to allow tickets to be used across a NAT boundary or when using multi-homed systems. This option is valid in the kinit [appdefault] section only. max_life =lifetime Sets the maximum lifetime of the ticket, with a total lifetime of lifetime. The values for lifetime follow the format described in the [libdefaults] section above. This option is obsolete and will be removed in a future release of the Solaris operating system. max_renewable_life =lifetime Requests renewable tickets, with a total lifetime of lifetime. The values for lifetime follow the format described in the [libde- faults] section above. This option is obsolete and will be removed in a future release of the Solaris operating system. rcmd_protocol = [ rcmdv1 | rcmdv2 ] Specifies which Kerberized "rcmd" protocol to use when using the Kerberized rlogin(1), rsh(1), rcp(1), or rdist(1) programs. The de- fault is to use "rcmdv2" by default, as this is the more secure and more recent update of the protocol. However, when talking to older MIT or SEAM-based "rcmd" servers, it may be necessary to force the new clients to use the older "rcmdv1" protocol. This option is valid only for the following applications: rlogin, rcp, rsh, and rdist. gkadmin = { help_url = http://localhost:8888/ab2/coll.384.1/SEAM } The following application defaults can be set to true or false: kinit forwardable = true proxiable = true renewable = true no_addresses = true max_life = delta_time max_renewable_life = delta_time See kinit(1) for the valid time duration formats you can specify for delta_time. In the following example, kinit will get forwardable tickets by default and telnet has three default behaviors specified: [appdefaults] kinit = { forwardable = true } telnet = { forward = true encrypt = true autologin = true } The application defaults specified here are overridden by those speci- fied in the [realms] section. [realms] This section contains subsections for Kerberos realms, where relation- subsection is the name of a realm. Each subsection contains relations that define the properties for that particular realm. The following re- lations may be specified in each [realms] subsection: kdc The name of a host running a KDC for that realm. An optional port number (separated from the hostname by a colon) may be included. admin_server Identifies the host where the Kerberos administration daemon (kad- mind) is running. Typically, this is the master KDC. application defaults Application defaults that are specific to a particular realm can be specified within a [realms] subsection. Realm-specific application defaults override the global defaults specified in the [appde- faults] section. auth_to_local_realm For use in the default realm, non-default realms can be equated with the default realm for authenticated name-to-local name map- ping. kpasswd_server Identifies the host where the Kerberos password-changing server is running. Typically, this is the same as host indicated in the ad- min_server. If this parameter is omitted, the host in admin_server is used. You can also specify a port number if the server indicated by kpasswd_server runs on a port other than 464 (the default). The format of this parameter is: hostname[:port]. kpasswd_protocol Identifies the protocol to be used when communicating with the server indicated by kpasswd_server. By default, this parameter is defined to be RPCSEC_GSS, which is the protocol used by SEAM-based administration servers. To be able to change a principal's password stored on non-SEAM-based Kerberos server, such as Microsoft Active Directory or MIT Kerberos, this value should be SET_CHANGE. This indicates that a non-RPC- based protocol will be used to communi- cate the password change request to the server in the kpasswd_server entry. verify_ap_req_nofail [true | false] If true, the local keytab file (/etc/krb5/krb5.keytab) must contain an entry for the local host principal, for example, host/foo.bar.com@FOO.COM. This entry is needed to verify that the TGT requested was issued by the same KDC that issued the key for the host principal. If undefined, the behavior is as if this option were set to true. Setting this value to false leaves the system vulnerable to DNS spoofing attacks. This parameter may be in the [realms] section to set it on a per-realm basis, or it may be in the [libdefaults] section to make it a network-wide setting for all realms. The parameters "forwardable", "proxiable", and "renew_lifetime" as de- scribed in the [libdefaults] section (see above) are also valid in the [realms] section. Notice that kpasswd_server and kpasswd_protocol are realm-specific pa- rameters. Most often, you need to specify them only when using a non- SEAM-based Kerberos server. Otherwise, the change request is sent over RPCSEC_GSS to the SEAM administration server. [domain_realm] This section provides a translation from a domain name or hostname to a Kerberos realm name. The relation can be a host name, or a domain name, where domain names are indicated by a period (`.') prefix. relation- value is the Kerberos realm name for that particular host or domain. Host names and domain names should be in lower case. If no translation entry applies, the host's realm is considered to be the hostname's domain portion converted to upper case. For example, the following [domain_realm] section maps crash.mit.edu into the TEST.ATHENA.MIT.EDU realm: [domain_realm] .mit.edu = ATHENA.MIT.EDU mit.edu = ATHENA.MIT.EDU crash.mit.edu = TEST.ATHENA.MIT.EDU .fubar.org = FUBAR.ORG fubar.org = FUBAR.ORG All other hosts in the mit.edu domain will map by default to the ATHENA.MIT.EDU realm, and all hosts in the fubar.org domain will map by default into the FUBAR.ORG realm. Note the entries for the hosts mit.edu and fubar.org. Without these entries, these hosts would be mapped into the Kerberos realms EDU and ORG, respectively. [logging] This section indicates how Kerberos programs are to perform logging. There are two types of relations for this section: relations to specify how to log and a relation to specify how to rotate kdc log files. The following relations may be defined to specify how to log. The same relation can be repeated if you want to assign it multiple logging methods. admin_server Specifies how to log the Kerberos administration daemon (kadmind). The default is FILE:/var/krb5/kadmin.log. default Specifies how to perform logging in the absence of explicit speci- fications otherwise. kdc Specifies how the KDC is to perform its logging. The default is FILE:/var/krb5/kdc.log. The admin_server, default, and kdc relations may have the following values: FILE:filename FILE=filename This value causes the entity's logging messages to go to the speci- fied file. If the `=' form is used, the file is overwritten. If the `:' form is used, the file is appended to. STDERR This value causes the entity's logging messages to go to its stan- dard error stream. CONSOLE This value causes the entity's logging messages to go to the con- sole, if the system supports it. DEVICE=devicename This causes the entity's logging messages to go to the specified device. SYSLOG[:severity[:facility]] This causes the entity's logging messages to go to the system log. The severity argument specifies the default severity of system log mes- sages. This may 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 may 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. The following relation may be defined to specify how to rotate kdc log files if the FILE: value is being used to log: kdc_rotate A relation subsection that enables kdc logging to be rotated to multiple files based on a time interval. This can be used to avoid logging to one file, which may grow too large and bring the KDC to a halt. The time interval for the rotation is specified by the period relation. The number of log files to be rotated is specified by the versions re- lation. Both the period and versions (described below) should be in- cluded in this subsection. And, this subsection applies only if the kdc relation has a FILE: value. The following relations may be specified for the kdc_rotate relation subsection: period=delta_time Specifies the time interval before a new log file is created. See the TimeFormats section in kinit(1) for the valid time duration formats you can specify for delta_time. If period is not specified or set to "never", no rotation will occur. Specifying a time interval does not mean that the log files will be ro- tated at the time interval based on real time. This is because the time interval is checked at each attempt to write a record to the log, or when logging is actually occurring. Therefore, rotation occurs only when logging has actually occurred for the specified time interval. versions=number Specifies how many previous versions will be saved before the rota- tion begins. A number will be appended to the log file, starting with 0 and ending with (number - 1). For example, if versions is set to 2, up to three logging files will be created (filename, filename.0, and filename.1) before the first one is overwritten to begin the rotation. Notice that if versions is not specified or set to 0, only one log file will be created, but it will be overwritten whenever the time interval is met. In the following example, the logging messages from the Kerberos admin- istration daemon will go to the console. The logging messages from the KDC will be appended to the /var/krb5/kdc.log, which will be rotated between twenty-one log files with a specified time interval of a day. [logging] admin_server = CONSOLE kdc = FILE:/export/logging/kadmin.log kdc_rotate = { period = 1d versions = 20 } [capaths] In order to perform direct (non-hierarchical) cross-realm authentica- tion, a database is needed to construct the authentication paths be- tween the realms. This section defines that database. A client will use this section to find the authentication path between its realm and the realm of the server. The server will use this section to verify the authentication path used by the client, by checking the transited field of the received ticket. There is a subsection for each participating realm, and each subsection has relations named for each of the realms. The relation-value is an intermediate realm which may participate in the cross-realm authentica- tion. The relations may be repeated if there is more than one interme- diate realm. A value of '.' means that the two realms share keys di- rectly, and no intermediate realms should be allowed to participate. There are n**2 possible entries in this table, but only those entries which will be needed on the client or the server need to be present. The client needs a subsection named for its local realm, with relations named for all the realms of servers it will need to authenticate with. A server needs a subsection named for each realm of the clients it will serve. For example, ANL.GOV, PNL.GOV, and NERSC.GOV all wish to use the ES.NET realm as an intermediate realm. ANL has a sub realm of TEST.ANL.GOV, which will authenticate with NERSC.GOV but not PNL.GOV. The [capath] section for ANL.GOV systems would look like this: [capaths] ANL.GOV = { TEST.ANL.GOV = . PNL.GOV = ES.NET NERSC.GOV = ES.NET ES.NET = . } TEST.ANL.GOV = { ANL.GOV = . } PNL.GOV = { ANL.GOV = ES.NET } NERSC.GOV = { ANL.GOV = ES.NET } ES.NET = { ANL.GOV = . } The [capath] section of the configuration file used on NERSC.GOV sys- tems would look like this: [capaths] NERSC.GOV = { ANL.GOV = ES.NET TEST.ANL.GOV = ES.NET TEST.ANL.GOV = ANL.GOV PNL.GOV = ES.NET ES.NET = . } ANL.GOV = { NERSC.GOV = ES.NET } PNL.GOV = { NERSC.GOV = ES.NET } ES.NET = { NERSC.GOV = . } TEST.ANL.GOV = { NERSC.GOV = ANL.GOV NERSC.GOV = ES.NET } In the above examples, the ordering is not important, except when the same relation is used more than once. The client will use this to de- termine the path. (It is not important to the server, since the tran- sited field is not sorted.) EXAMPLES Example 1: Sample file Here is an example of a generic krb5.conf file: [libdefaults] default_realm = ATHENA.MIT.EDU default_tkt_enctypes = des-cbc-crc default_tgs_enctypes = des-cbc-crc [realms] ATHENA.MIT.EDU = { kdc = kerberos.mit.edu kdc = kerberos-1.mit.edu kdc = kerberos-2.mit.edu admin_server = kerberos.mit.edu auth_to_local_realm = KRBDEV.ATHENA.MIT.EDU } FUBAR.ORG = { kdc = kerberos.fubar.org kdc = kerberos-1.fubar.org admin_server = kerberos.fubar.org } [domain_realm] .mit.edu = ATHENA.MIT.EDU mit.edu = ATHENA.MIT.EDU FILES /var/krb5/kdc.log KDC logging file ATTRIBUTES See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Evolving | +-----------------------------+-----------------------------+ SEE ALSO kinit(1), rcp(1), rdist(1), rlogin(1), rsh(1), syslog(3C), SEAM(5), at- tributes(5) NOTES If the krb5.conf file is not formatted properly, the telnet command will fail. However, the dtlogin and login commands will still succeed, even if the krb5.conf file is specified as required for the commands. If this occurs, the following error message will be displayed: Error initializing krb5: Improper format of item To bypass any other problems that may occur, you should fix the file as soon as possible. The max_life and max_renewable_life options are obsolete and will be removed in a future release of the Solaris operating system. SunOS 5.10 25 May 2004 krb5.conf(4)
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | FILES | ATTRIBUTES | SEE ALSO | NOTES
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