1KRB5.CONF(5) MIT Kerberos KRB5.CONF(5)
2
6 krb5.conf - Kerberos configuration file
7 The krb5.conf file contains Kerberos configuration information, includ‐
9 ing the locations of KDCs and admin servers for the Kerberos realms of
10 interest, defaults for the current realm and for Kerberos applications,
11 and mappings of hostnames onto Kerberos realms. Normally, you should
12 install your krb5.conf file in the directory /etc. You can override
13 the default location by setting the environment variable KRB5_CONFIG.
14 Multiple colon-separated filenames may be specified in KRB5_CONFIG; all
15 files which are present will be read. Starting in release 1.14, direc‐
16 tory names can also be specified in KRB5_CONFIG; all files within the
17 directory whose names consist solely of alphanumeric characters,
18 dashes, or underscores will be read.
19
21 The krb5.conf file is set up in the style of a Windows INI file. Lines
22 beginning with '#' or ';' (possibly after initial whitespace) are ig‐
23 nored as comments. Sections are headed by the section name, in square
24 brackets. Each section may contain zero or more relations, of the
25 form:
26 foo = bar
28 or:
30 fubar = {
32 foo = bar
33 baz = quux
34 }
35 Placing a '*' after the closing bracket of a section name indicates
37 that the section is final, meaning that if the same section appears
38 within a later file specified in KRB5_CONFIG, it will be ignored. A
39 subsection can be marked as final by placing a '*' after either the tag
40 name or the closing brace.
41 The krb5.conf file can include other files using either of the follow‐
43 ing directives at the beginning of a line:
44 include FILENAME
46 includedir DIRNAME
47 FILENAME or DIRNAME should be an absolute path. The named file or di‐
49 rectory must exist and be readable. Including a directory includes all
50 files within the directory whose names consist solely of alphanumeric
51 characters, dashes, or underscores. Starting in release 1.15, files
52 with names ending in ".conf" are also included, unless the name begins
53 with ".". Included profile files are syntactically independent of
54 their parents, so each included file must begin with a section header.
55 Starting in release 1.17, files are read in alphanumeric order; in pre‐
56 vious releases, they may be read in any order.
57 The krb5.conf file can specify that configuration should be obtained
59 from a loadable module, rather than the file itself, using the follow‐
60 ing directive at the beginning of a line before any section headers:
61 module MODULEPATH:RESIDUAL
63 MODULEPATH may be relative to the library path of the krb5 installa‐
65 tion, or it may be an absolute path. RESIDUAL is provided to the mod‐
66 ule at initialization time. If krb5.conf uses a module directive,
67 kdc.conf(5) should also use one if it exists.
68
70 The krb5.conf file may contain the following sections:
71 ┌───────────────┬────────────────────────────┐
73 │[libdefaults] │ Settings used by the Ker‐ │
74 │ │ beros V5 library │
75 ├───────────────┼────────────────────────────┤
76 │[realms] │ Realm-specific contact in‐ │
77 │ │ formation and settings │
78 ├───────────────┼────────────────────────────┤
79 │[domain_realm] │ Maps server hostnames to │
80 │ │ Kerberos realms │
81 ├───────────────┼────────────────────────────┤
82 │[capaths] │ Authentication paths for │
83 │ │ non-hierarchical │
84 │ │ cross-realm │
85 ├───────────────┼────────────────────────────┤
86 │[appdefaults] │ Settings used by some Ker‐ │
87 │ │ beros V5 applications │
88 ├───────────────┼────────────────────────────┤
89 │[plugins] │ Controls plugin module │
90 │ │ registration │
91 └───────────────┴────────────────────────────┘
92 Additionally, krb5.conf may include any of the relations described in
94 kdc.conf(5), but it is not a recommended practice.
95 [libdefaults]
97 The libdefaults section may contain any of the following relations:
98 allow_weak_crypto
100 If this flag is set to false, then weak encryption types (as
101 noted in Encryption_types in kdc.conf(5)) will be filtered out
102 of the lists default_tgs_enctypes, default_tkt_enctypes, and
103 permitted_enctypes. The default value for this tag is false.
104 canonicalize
106 If this flag is set to true, initial ticket requests to the KDC
107 will request canonicalization of the client principal name, and
108 answers with different client principals than the requested
109 principal will be accepted. The default value is false.
110 ccache_type
112 This parameter determines the format of credential cache types
113 created by kinit(1) or other programs. The default value is 4,
114 which represents the most current format. Smaller values can be
115 used for compatibility with very old implementations of Kerberos
116 which interact with credential caches on the same host.
117 clockskew
119 Sets the maximum allowable amount of clockskew in seconds that
120 the library will tolerate before assuming that a Kerberos mes‐
121 sage is invalid. The default value is 300 seconds, or five min‐
122 utes.
123 The clockskew setting is also used when evaluating ticket start
125 and expiration times. For example, tickets that have reached
126 their expiration time can still be used (and renewed if they are
127 renewable tickets) if they have been expired for a shorter dura‐
128 tion than the clockskew setting.
129 default_ccache_name
131 This relation specifies the name of the default credential
132 cache. The default is FILE:/tmp/krb5cc_%{uid}. This relation
133 is subject to parameter expansion (see below). New in release
134 1.11.
135 default_client_keytab_name
137 This relation specifies the name of the default keytab for ob‐
138 taining client credentials. The default is FILE:/var/ker‐
139 beros/krb5/user/%{euid}/client.keytab. This relation is subject
140 to parameter expansion (see below). New in release 1.11.
141 default_keytab_name
143 This relation specifies the default keytab name to be used by
144 application servers such as sshd. The default is
145 FILE:/etc/krb5.keytab. This relation is subject to parameter
146 expansion (see below).
147 default_rcache_name
149 This relation specifies the name of the default replay cache.
150 The default is dfl:. This relation is subject to parameter ex‐
151 pansion (see below). New in release 1.18.
152 default_realm
154 Identifies the default Kerberos realm for the client. Set its
155 value to your Kerberos realm. If this value is not set, then a
156 realm must be specified with every Kerberos principal when in‐
157 voking programs such as kinit(1).
158 default_tgs_enctypes
160 Identifies the supported list of session key encryption types
161 that the client should request when making a TGS-REQ, in order
162 of preference from highest to lowest. The list may be delimited
163 with commas or whitespace. See Encryption_types in kdc.conf(5)
164 for a list of the accepted values for this tag. Starting in re‐
165 lease 1.18, the default value is the value of permitted_enc‐
166 types. For previous releases or if permitted_enctypes is not
167 set, the default value is aes256-cts-hmac-sha1-96
168 aes128-cts-hmac-sha1-96 aes256-cts-hmac-sha384-192
169 aes128-cts-hmac-sha256-128 arcfour-hmac-md5 camellia256-cts-cmac
170 camellia128-cts-cmac.
171 Do not set this unless required for specific backward compati‐
173 bility purposes; stale values of this setting can prevent
174 clients from taking advantage of new stronger enctypes when the
175 libraries are upgraded.
176 default_tkt_enctypes
178 Identifies the supported list of session key encryption types
179 that the client should request when making an AS-REQ, in order
180 of preference from highest to lowest. The format is the same as
181 for default_tgs_enctypes. Starting in release 1.18, the default
182 value is the value of permitted_enctypes. For previous releases
183 or if permitted_enctypes is not set, the default value is
184 aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
185 aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128 arc‐
186 four-hmac-md5 camellia256-cts-cmac camellia128-cts-cmac.
187 Do not set this unless required for specific backward compati‐
189 bility purposes; stale values of this setting can prevent
190 clients from taking advantage of new stronger enctypes when the
191 libraries are upgraded.
192 dns_canonicalize_hostname
194 Indicate whether name lookups will be used to canonicalize host‐
195 names for use in service principal names. Setting this flag to
196 false can improve security by reducing reliance on DNS, but
197 means that short hostnames will not be canonicalized to
198 fully-qualified hostnames. If this option is set to fallback
199 (new in release 1.18), DNS canonicalization will only be per‐
200 formed the server hostname is not found with the original name
201 when requesting credentials. The default value is true.
202 dns_lookup_kdc
204 Indicate whether DNS SRV records should be used to locate the
205 KDCs and other servers for a realm, if they are not listed in
206 the krb5.conf information for the realm. (Note that the ad‐
207 min_server entry must be in the krb5.conf realm information in
208 order to contact kadmind, because the DNS implementation for
209 kadmin is incomplete.)
210 Enabling this option does open up a type of denial-of-service
212 attack, if someone spoofs the DNS records and redirects you to
213 another server. However, it's no worse than a denial of ser‐
214 vice, because that fake KDC will be unable to decode anything
215 you send it (besides the initial ticket request, which has no
216 encrypted data), and anything the fake KDC sends will not be
217 trusted without verification using some secret that it won't
218 know.
219 dns_uri_lookup
221 Indicate whether DNS URI records should be used to locate the
222 KDCs and other servers for a realm, if they are not listed in
223 the krb5.conf information for the realm. SRV records are used
224 as a fallback if no URI records were found. The default value
225 is true. New in release 1.15.
226 enforce_ok_as_delegate
228 If this flag to true, GSSAPI credential delegation will be dis‐
229 abled when the ok-as-delegate flag is not set in the service
230 ticket. If this flag is false, the ok-as-delegate ticket flag
231 is only enforced when an application specifically requests en‐
232 forcement. The default value is false.
233 err_fmt
235 This relation allows for custom error message formatting. If a
236 value is set, error messages will be formatted by substituting a
237 normal error message for %M and an error code for %C in the
238 value.
239 extra_addresses
241 This allows a computer to use multiple local addresses, in order
242 to allow Kerberos to work in a network that uses NATs while
243 still using address-restricted tickets. The addresses should be
244 in a comma-separated list. This option has no effect if noad‐
245 dresses is true.
246 forwardable
248 If this flag is true, initial tickets will be forwardable by de‐
249 fault, if allowed by the KDC. The default value is false.
250 ignore_acceptor_hostname
252 When accepting GSSAPI or krb5 security contexts for host-based
253 service principals, ignore any hostname passed by the calling
254 application, and allow clients to authenticate to any service
255 principal in the keytab matching the service name and realm name
256 (if given). This option can improve the administrative flexi‐
257 bility of server applications on multihomed hosts, but could
258 compromise the security of virtual hosting environments. The
259 default value is false. New in release 1.10.
260 k5login_authoritative
262 If this flag is true, principals must be listed in a local
263 user's k5login file to be granted login access, if a .k5login(5)
264 file exists. If this flag is false, a principal may still be
265 granted login access through other mechanisms even if a k5login
266 file exists but does not list the principal. The default value
267 is true.
268 k5login_directory
270 If set, the library will look for a local user's k5login file
271 within the named directory, with a filename corresponding to the
272 local username. If not set, the library will look for k5login
273 files in the user's home directory, with the filename .k5login.
274 For security reasons, .k5login files must be owned by the local
275 user or by root.
276 kcm_mach_service
278 On macOS only, determines the name of the bootstrap service used
279 to contact the KCM daemon for the KCM credential cache type. If
280 the value is -, Mach RPC will not be used to contact the KCM
281 daemon. The default value is org.h5l.kcm.
282 kcm_socket
284 Determines the path to the Unix domain socket used to access the
285 KCM daemon for the KCM credential cache type. If the value is
286 -, Unix domain sockets will not be used to contact the KCM dae‐
287 mon. The default value is /var/run/.heim_org.h5l.kcm-socket.
288 kdc_default_options
290 Default KDC options (Xored for multiple values) when requesting
291 initial tickets. By default it is set to 0x00000010
292 (KDC_OPT_RENEWABLE_OK).
293 kdc_timesync
295 Accepted values for this relation are 1 or 0. If it is nonzero,
296 client machines will compute the difference between their time
297 and the time returned by the KDC in the timestamps in the tick‐
298 ets and use this value to correct for an inaccurate system clock
299 when requesting service tickets or authenticating to services.
300 This corrective factor is only used by the Kerberos library; it
301 is not used to change the system clock. The default value is 1.
302 noaddresses
304 If this flag is true, requests for initial tickets will not be
305 made with address restrictions set, allowing the tickets to be
306 used across NATs. The default value is true.
307 permitted_enctypes
309 Identifies the encryption types that servers will permit for
310 session keys and for ticket and authenticator encryption, or‐
311 dered by preference from highest to lowest. Starting in release
312 1.18, this tag also acts as the default value for de‐
313 fault_tgs_enctypes and default_tkt_enctypes. The default value
314 for this tag is aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
315 aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128 arc‐
316 four-hmac-md5 camellia256-cts-cmac camellia128-cts-cmac.
317 plugin_base_dir
319 If set, determines the base directory where krb5 plugins are lo‐
320 cated. The default value is the krb5/plugins subdirectory of
321 the krb5 library directory. This relation is subject to parame‐
322 ter expansion (see below) in release 1.17 and later.
323 preferred_preauth_types
325 This allows you to set the preferred preauthentication types
326 which the client will attempt before others which may be adver‐
327 tised by a KDC. The default value for this setting is "17, 16,
328 15, 14", which forces libkrb5 to attempt to use PKINIT if it is
329 supported.
330 proxiable
332 If this flag is true, initial tickets will be proxiable by de‐
333 fault, if allowed by the KDC. The default value is false.
334 qualify_shortname
336 If this string is set, it determines the domain suffix for sin‐
337 gle-component hostnames when DNS canonicalization is not used
338 (either because dns_canonicalize_hostname is false or because
339 forward canonicalization failed). The default value is the
340 first search domain of the system's DNS configuration. To dis‐
341 able qualification of shortnames, set this relation to the empty
342 string with qualify_shortname = "". (New in release 1.18.)
343 radius_md5_fips_override
345 Downstream-only option to enable use of MD5 in RADIUS communica‐
346 tion (libkrad). This allows for local (or protected tunnel)
347 communication with a RADIUS server that doesn't use krad (e.g.,
348 freeradius) while in FIPS mode.
349 rdns If this flag is true, reverse name lookup will be used in addi‐
351 tion to forward name lookup to canonicalizing hostnames for use
352 in service principal names. If dns_canonicalize_hostname is set
353 to false, this flag has no effect. The default value is true.
354 realm_try_domains
356 Indicate whether a host's domain components should be used to
357 determine the Kerberos realm of the host. The value of this
358 variable is an integer: -1 means not to search, 0 means to try
359 the host's domain itself, 1 means to also try the domain's imme‐
360 diate parent, and so forth. The library's usual mechanism for
361 locating Kerberos realms is used to determine whether a domain
362 is a valid realm, which may involve consulting DNS if
363 dns_lookup_kdc is set. The default is not to search domain com‐
364 ponents.
365 renew_lifetime
367 (duration string.) Sets the default renewable lifetime for ini‐
368 tial ticket requests. The default value is 0.
369 spake_preauth_groups
371 A whitespace or comma-separated list of words which specifies
372 the groups allowed for SPAKE preauthentication. The possible
373 values are:
374 ┌─────────────┬────────────────────────────┐
376 │edwards25519 │ Edwards25519 curve (RFC │
377 │ │ 7748) │
378 ├─────────────┼────────────────────────────┤
379 │P-256 │ NIST P-256 curve (RFC │
380 │ │ 5480) │
381 ├─────────────┼────────────────────────────┤
382 │P-384 │ NIST P-384 curve (RFC │
383 │ │ 5480) │
384 ├─────────────┼────────────────────────────┤
385 │P-521 │ NIST P-521 curve (RFC │
386 │ │ 5480) │
387 └─────────────┴────────────────────────────┘
388 The default value for the client is edwards25519. The default
390 value for the KDC is empty. New in release 1.17.
391 ticket_lifetime
393 (duration string.) Sets the default lifetime for initial ticket
394 requests. The default value is 1 day.
395 udp_preference_limit
397 When sending a message to the KDC, the library will try using
398 TCP before UDP if the size of the message is above udp_prefer‐
399 ence_limit. If the message is smaller than udp_prefer‐
400 ence_limit, then UDP will be tried before TCP. Regardless of
401 the size, both protocols will be tried if the first attempt
402 fails.
403 verify_ap_req_nofail
405 If this flag is true, then an attempt to verify initial creden‐
406 tials will fail if the client machine does not have a keytab.
407 The default value is false.
408 client_aware_channel_bindings
410 If this flag is true, then all application protocol authentica‐
411 tion requests will be flagged to indicate that the application
412 supports channel bindings when operating over a secure channel.
413 The default value is false.
414 [realms]
416 Each tag in the [realms] section of the file is the name of a Kerberos
417 realm. The value of the tag is a subsection with relations that define
418 the properties of that particular realm. For each realm, the following
419 tags may be specified in the realm's subsection:
420 admin_server
422 Identifies the host where the administration server is running.
423 Typically, this is the primary Kerberos server. This tag must
424 be given a value in order to communicate with the kadmind(8)
425 server for the realm.
426 auth_to_local
428 This tag allows you to set a general rule for mapping principal
429 names to local user names. It will be used if there is not an
430 explicit mapping for the principal name that is being trans‐
431 lated. The possible values are:
432 RULE:exp
434 The local name will be formulated from exp.
435 The format for exp is [n:string](regexp)s/pattern/re‐
437 placement/g. The integer n indicates how many components
438 the target principal should have. If this matches, then
439 a string will be formed from string, substituting the
440 realm of the principal for $0 and the n'th component of
441 the principal for $n (e.g., if the principal was john‐
442 doe/admin then [2:$2$1foo] would result in the string ad‐
443 minjohndoefoo). If this string matches regexp, then the
444 s//[g] substitution command will be run over the string.
445 The optional g will cause the substitution to be global
446 over the string, instead of replacing only the first
447 match in the string.
448 DEFAULT
450 The principal name will be used as the local user name.
451 If the principal has more than one component or is not in
452 the default realm, this rule is not applicable and the
453 conversion will fail.
454 For example:
456 [realms]
458 ATHENA.MIT.EDU = {
459 auth_to_local = RULE:[2:$1](johndoe)s/^.*$/guest/
460 auth_to_local = RULE:[2:$1;$2](^.*;admin$)s/;admin$//
461 auth_to_local = RULE:[2:$2](^.*;root)s/^.*$/root/
462 auth_to_local = DEFAULT
463 }
464 would result in any principal without root or admin as the sec‐
466 ond component to be translated with the default rule. A princi‐
467 pal with a second component of admin will become its first com‐
468 ponent. root will be used as the local name for any principal
469 with a second component of root. The exception to these two
470 rules are any principals johndoe/*, which will always get the
471 local name guest.
472 auth_to_local_names
474 This subsection allows you to set explicit mappings from princi‐
475 pal names to local user names. The tag is the mapping name, and
476 the value is the corresponding local user name.
477 default_domain
479 This tag specifies the domain used to expand hostnames when
480 translating Kerberos 4 service principals to Kerberos 5 princi‐
481 pals (for example, when converting rcmd.hostname to host/host‐
482 name.domain).
483 disable_encrypted_timestamp
485 If this flag is true, the client will not perform encrypted
486 timestamp preauthentication if requested by the KDC. Setting
487 this flag can help to prevent dictionary attacks by active at‐
488 tackers, if the realm's KDCs support SPAKE preauthentication or
489 if initial authentication always uses another mechanism or al‐
490 ways uses FAST. This flag persists across client referrals dur‐
491 ing initial authentication. This flag does not prevent the KDC
492 from offering encrypted timestamp. New in release 1.17.
493 http_anchors
495 When KDCs and kpasswd servers are accessed through HTTPS prox‐
496 ies, this tag can be used to specify the location of the CA cer‐
497 tificate which should be trusted to issue the certificate for a
498 proxy server. If left unspecified, the system-wide default set
499 of CA certificates is used.
500 The syntax for values is similar to that of values for the
502 pkinit_anchors tag:
503 FILE: filename
505 filename is assumed to be the name of an OpenSSL-style ca-bundle
507 file.
508 DIR: dirname
510 dirname is assumed to be an directory which contains CA certifi‐
512 cates. All files in the directory will be examined; if they
513 contain certificates (in PEM format), they will be used.
514 ENV: envvar
516 envvar specifies the name of an environment variable which has
518 been set to a value conforming to one of the previous values.
519 For example, ENV:X509_PROXY_CA, where environment variable
520 X509_PROXY_CA has been set to FILE:/tmp/my_proxy.pem.
521 kdc The name or address of a host running a KDC for that realm. An
523 optional port number, separated from the hostname by a colon,
524 may be included. If the name or address contains colons (for
525 example, if it is an IPv6 address), enclose it in square brack‐
526 ets to distinguish the colon from a port separator. For your
527 computer to be able to communicate with the KDC for each realm,
528 this tag must be given a value in each realm subsection in the
529 configuration file, or there must be DNS SRV records specifying
530 the KDCs.
531 kpasswd_server
533 Points to the server where all the password changes are per‐
534 formed. If there is no such entry, DNS will be queried (unless
535 forbidden by dns_lookup_kdc). Finally, port 464 on the ad‐
536 min_server host will be tried.
537 master_kdc
539 The name for primary_kdc prior to release 1.19. Its value is
540 used as a fallback if primary_kdc is not specified.
541 primary_kdc
543 Identifies the primary KDC(s). Currently, this tag is used in
544 only one case: If an attempt to get credentials fails because of
545 an invalid password, the client software will attempt to contact
546 the primary KDC, in case the user's password has just been
547 changed, and the updated database has not been propagated to the
548 replica servers yet. New in release 1.19.
549 v4_instance_convert
551 This subsection allows the administrator to configure exceptions
552 to the default_domain mapping rule. It contains V4 instances
553 (the tag name) which should be translated to some specific host‐
554 name (the tag value) as the second component in a Kerberos V5
555 principal name.
556 v4_realm
558 This relation is used by the krb524 library routines when con‐
559 verting a V5 principal name to a V4 principal name. It is used
560 when the V4 realm name and the V5 realm name are not the same,
561 but still share the same principal names and passwords. The tag
562 value is the Kerberos V4 realm name.
563 [domain_realm]
565 The [domain_realm] section provides a translation from a domain name or
566 hostname to a Kerberos realm name. The tag name can be a host name or
567 domain name, where domain names are indicated by a prefix of a period
568 (.). The value of the relation is the Kerberos realm name for that
569 particular host or domain. A host name relation implicitly provides
570 the corresponding domain name relation, unless an explicit domain name
571 relation is provided. The Kerberos realm may be identified either in
572 the realms section or using DNS SRV records. Host names and domain
573 names should be in lower case. For example:
574 [domain_realm]
576 crash.mit.edu = TEST.ATHENA.MIT.EDU
577 .dev.mit.edu = TEST.ATHENA.MIT.EDU
578 mit.edu = ATHENA.MIT.EDU
579 maps the host with the name crash.mit.edu into the TEST.ATHENA.MIT.EDU
581 realm. The second entry maps all hosts under the domain dev.mit.edu
582 into the TEST.ATHENA.MIT.EDU realm, but not the host with the name
583 dev.mit.edu. That host is matched by the third entry, which maps the
584 host mit.edu and all hosts under the domain mit.edu that do not match a
585 preceding rule into the realm ATHENA.MIT.EDU.
586 If no translation entry applies to a hostname used for a service prin‐
588 cipal for a service ticket request, the library will try to get a re‐
589 ferral to the appropriate realm from the client realm's KDC. If that
590 does not succeed, the host's realm is considered to be the hostname's
591 domain portion converted to uppercase, unless the realm_try_domains
592 setting in [libdefaults] causes a different parent domain to be used.
593 [capaths]
595 In order to perform direct (non-hierarchical) cross-realm authentica‐
596 tion, configuration is needed to determine the authentication paths be‐
597 tween realms.
598 A client will use this section to find the authentication path between
600 its realm and the realm of the server. The server will use this sec‐
601 tion to verify the authentication path used by the client, by checking
602 the transited field of the received ticket.
603 There is a tag for each participating client realm, and each tag has
605 subtags for each of the server realms. The value of the subtags is an
606 intermediate realm which may participate in the cross-realm authentica‐
607 tion. The subtags may be repeated if there is more then one intermedi‐
608 ate realm. A value of "." means that the two realms share keys di‐
609 rectly, and no intermediate realms should be allowed to participate.
610 Only those entries which will be needed on the client or the server
612 need to be present. A client needs a tag for its local realm with sub‐
613 tags for all the realms of servers it will need to authenticate to. A
614 server needs a tag for each realm of the clients it will serve, with a
615 subtag of the server realm.
616 For example, ANL.GOV, PNL.GOV, and NERSC.GOV all wish to use the ES.NET
618 realm as an intermediate realm. ANL has a sub realm of TEST.ANL.GOV
619 which will authenticate with NERSC.GOV but not PNL.GOV. The [capaths]
620 section for ANL.GOV systems would look like this:
621 [capaths]
623 ANL.GOV = {
624 TEST.ANL.GOV = .
625 PNL.GOV = ES.NET
626 NERSC.GOV = ES.NET
627 ES.NET = .
628 }
629 TEST.ANL.GOV = {
630 ANL.GOV = .
631 }
632 PNL.GOV = {
633 ANL.GOV = ES.NET
634 }
635 NERSC.GOV = {
636 ANL.GOV = ES.NET
637 }
638 ES.NET = {
639 ANL.GOV = .
640 }
641 The [capaths] section of the configuration file used on NERSC.GOV sys‐
643 tems would look like this:
644 [capaths]
646 NERSC.GOV = {
647 ANL.GOV = ES.NET
648 TEST.ANL.GOV = ES.NET
649 TEST.ANL.GOV = ANL.GOV
650 PNL.GOV = ES.NET
651 ES.NET = .
652 }
653 ANL.GOV = {
654 NERSC.GOV = ES.NET
655 }
656 PNL.GOV = {
657 NERSC.GOV = ES.NET
658 }
659 ES.NET = {
660 NERSC.GOV = .
661 }
662 TEST.ANL.GOV = {
663 NERSC.GOV = ANL.GOV
664 NERSC.GOV = ES.NET
665 }
666 When a subtag is used more than once within a tag, clients will use the
668 order of values to determine the path. The order of values is not im‐
669 portant to servers.
670 [appdefaults]
672 Each tag in the [appdefaults] section names a Kerberos V5 application
673 or an option that is used by some Kerberos V5 application[s]. The
674 value of the tag defines the default behaviors for that application.
675 For example:
677 [appdefaults]
679 telnet = {
680 ATHENA.MIT.EDU = {
681 option1 = false
682 }
683 }
684 telnet = {
685 option1 = true
686 option2 = true
687 }
688 ATHENA.MIT.EDU = {
689 option2 = false
690 }
691 option2 = true
692 The above four ways of specifying the value of an option are shown in
694 order of decreasing precedence. In this example, if telnet is running
695 in the realm EXAMPLE.COM, it should, by default, have option1 and op‐
696 tion2 set to true. However, a telnet program in the realm
697 ATHENA.MIT.EDU should have option1 set to false and option2 set to
698 true. Any other programs in ATHENA.MIT.EDU should have option2 set to
699 false by default. Any programs running in other realms should have op‐
700 tion2 set to true.
701 The list of specifiable options for each application may be found in
703 that application's man pages. The application defaults specified here
704 are overridden by those specified in the realms section.
705 [plugins]
707 • pwqual interface
708 • kadm5_hook interface
710 • clpreauth and kdcpreauth interfaces
712 Tags in the [plugins] section can be used to register dynamic plugin
714 modules and to turn modules on and off. Not every krb5 pluggable in‐
715 terface uses the [plugins] section; the ones that do are documented
716 here.
717 New in release 1.9.
719 Each pluggable interface corresponds to a subsection of [plugins]. All
721 subsections support the same tags:
722 disable
724 This tag may have multiple values. If there are values for this
725 tag, then the named modules will be disabled for the pluggable
726 interface.
727 enable_only
729 This tag may have multiple values. If there are values for this
730 tag, then only the named modules will be enabled for the plug‐
731 gable interface.
732 module This tag may have multiple values. Each value is a string of
734 the form modulename:pathname, which causes the shared object lo‐
735 cated at pathname to be registered as a dynamic module named
736 modulename for the pluggable interface. If pathname is not an
737 absolute path, it will be treated as relative to the
738 plugin_base_dir value from [libdefaults].
739 For pluggable interfaces where module order matters, modules registered
741 with a module tag normally come first, in the order they are regis‐
742 tered, followed by built-in modules in the order they are documented
743 below. If enable_only tags are used, then the order of those tags
744 overrides the normal module order.
745 The following subsections are currently supported within the [plugins]
747 section:
748 ccselect interface
750 The ccselect subsection controls modules for credential cache selection
751 within a cache collection. In addition to any registered dynamic mod‐
752 ules, the following built-in modules exist (and may be disabled with
753 the disable tag):
754 k5identity
756 Uses a .k5identity file in the user's home directory to select a
757 client principal
758 realm Uses the service realm to guess an appropriate cache from the
760 collection
761 hostname
763 If the service principal is host-based, uses the service host‐
764 name to guess an appropriate cache from the collection
765 pwqual interface
767 The pwqual subsection controls modules for the password quality inter‐
768 face, which is used to reject weak passwords when passwords are
769 changed. The following built-in modules exist for this interface:
770 dict Checks against the realm dictionary file
772 empty Rejects empty passwords
774 hesiod Checks against user information stored in Hesiod (only if Ker‐
776 beros was built with Hesiod support)
777 princ Checks against components of the principal name
779 kadm5_hook interface
781 The kadm5_hook interface provides plugins with information on principal
782 creation, modification, password changes and deletion. This interface
783 can be used to write a plugin to synchronize MIT Kerberos with another
784 database such as Active Directory. No plugins are built in for this
785 interface.
786 kadm5_auth interface
788 The kadm5_auth section (introduced in release 1.16) controls modules
789 for the kadmin authorization interface, which determines whether a
790 client principal is allowed to perform a kadmin operation. The follow‐
791 ing built-in modules exist for this interface:
792 acl This module reads the kadm5.acl(5) file, and authorizes opera‐
794 tions which are allowed according to the rules in the file.
795 self This module authorizes self-service operations including pass‐
797 word changes, creation of new random keys, fetching the client's
798 principal record or string attributes, and fetching the policy
799 record associated with the client principal.
800 clpreauth and kdcpreauth interfaces
802 The clpreauth and kdcpreauth interfaces allow plugin modules to provide
803 client and KDC preauthentication mechanisms. The following built-in
804 modules exist for these interfaces:
805 pkinit This module implements the PKINIT preauthentication mechanism.
807 encrypted_challenge
809 This module implements the encrypted challenge FAST factor.
810 encrypted_timestamp
812 This module implements the encrypted timestamp mechanism.
813 hostrealm interface
815 The hostrealm section (introduced in release 1.12) controls modules for
816 the host-to-realm interface, which affects the local mapping of host‐
817 names to realm names and the choice of default realm. The following
818 built-in modules exist for this interface:
819 profile
821 This module consults the [domain_realm] section of the profile
822 for authoritative host-to-realm mappings, and the default_realm
823 variable for the default realm.
824 dns This module looks for DNS records for fallback host-to-realm
826 mappings and the default realm. It only operates if the
827 dns_lookup_realm variable is set to true.
828 domain This module applies heuristics for fallback host-to-realm map‐
830 pings. It implements the realm_try_domains variable, and uses
831 the uppercased parent domain of the hostname if that does not
832 produce a result.
833 localauth interface
835 The localauth section (introduced in release 1.12) controls modules for
836 the local authorization interface, which affects the relationship be‐
837 tween Kerberos principals and local system accounts. The following
838 built-in modules exist for this interface:
839 default
841 This module implements the DEFAULT type for auth_to_local val‐
842 ues.
843 rule This module implements the RULE type for auth_to_local values.
845 names This module looks for an auth_to_local_names mapping for the
847 principal name.
848 auth_to_local
850 This module processes auth_to_local values in the default
851 realm's section, and applies the default method if no
852 auth_to_local values exist.
853 k5login
855 This module authorizes a principal to a local account according
856 to the account's .k5login(5) file.
857 an2ln This module authorizes a principal to a local account if the
859 principal name maps to the local account name.
860 certauth interface
862 The certauth section (introduced in release 1.16) controls modules for
863 the certificate authorization interface, which determines whether a
864 certificate is allowed to preauthenticate a user via PKINIT. The fol‐
865 lowing built-in modules exist for this interface:
866 pkinit_san
868 This module authorizes the certificate if it contains a PKINIT
869 Subject Alternative Name for the requested client principal, or
870 a Microsoft UPN SAN matching the principal if pkinit_allow_upn
871 is set to true for the realm.
872 pkinit_eku
874 This module rejects the certificate if it does not contain an
875 Extended Key Usage attribute consistent with the
876 pkinit_eku_checking value for the realm.
877 dbmatch
879 This module authorizes or rejects the certificate according to
880 whether it matches the pkinit_cert_match string attribute on the
881 client principal, if that attribute is present.
882
884 NOTE:
885 The following are PKINIT-specific options. These values may be
886 specified in [libdefaults] as global defaults, or within a
887 realm-specific subsection of [libdefaults], or may be specified as
888 realm-specific values in the [realms] section. A realm-specific
889 value overrides, not adds to, a generic [libdefaults] specification.
890 The search order is:
891 1. realm-specific subsection of [libdefaults]:
893 [libdefaults]
895 EXAMPLE.COM = {
896 pkinit_anchors = FILE:/usr/local/example.com.crt
897 }
898 2. realm-specific value in the [realms] section:
900 [realms]
902 OTHERREALM.ORG = {
903 pkinit_anchors = FILE:/usr/local/otherrealm.org.crt
904 }
905 3. generic value in the [libdefaults] section:
907 [libdefaults]
909 pkinit_anchors = DIR:/usr/local/generic_trusted_cas/
910 Specifying PKINIT identity information
912 The syntax for specifying Public Key identity, trust, and revocation
913 information for PKINIT is as follows:
914 FILE:filename[,keyfilename]
916 This option has context-specific behavior.
917 In pkinit_identity or pkinit_identities, filename specifies the
919 name of a PEM-format file containing the user's certificate. If
920 keyfilename is not specified, the user's private key is expected
921 to be in filename as well. Otherwise, keyfilename is the name
922 of the file containing the private key.
923 In pkinit_anchors or pkinit_pool, filename is assumed to be the
925 name of an OpenSSL-style ca-bundle file.
926 DIR:dirname
928 This option has context-specific behavior.
929 In pkinit_identity or pkinit_identities, dirname specifies a di‐
931 rectory with files named *.crt and *.key where the first part of
932 the file name is the same for matching pairs of certificate and
933 private key files. When a file with a name ending with .crt is
934 found, a matching file ending with .key is assumed to contain
935 the private key. If no such file is found, then the certificate
936 in the .crt is not used.
937 In pkinit_anchors or pkinit_pool, dirname is assumed to be an
939 OpenSSL-style hashed CA directory where each CA cert is stored
940 in a file named hash-of-ca-cert.#. This infrastructure is en‐
941 couraged, but all files in the directory will be examined and if
942 they contain certificates (in PEM format), they will be used.
943 In pkinit_revoke, dirname is assumed to be an OpenSSL-style
945 hashed CA directory where each revocation list is stored in a
946 file named hash-of-ca-cert.r#. This infrastructure is encour‐
947 aged, but all files in the directory will be examined and if
948 they contain a revocation list (in PEM format), they will be
949 used.
950 PKCS12:filename
952 filename is the name of a PKCS #12 format file, containing the
953 user's certificate and private key.
954 PKCS11:[module_name=]modname[:slotid=slot-id][:token=token-label][:cer‐
956 tid=cert-id][:certlabel=cert-label]
957 All keyword/values are optional. modname specifies the location
958 of a library implementing PKCS #11. If a value is encountered
959 with no keyword, it is assumed to be the modname. If no mod‐
960 ule-name is specified, the default is opensc-pkcs11.so. slotid=
961 and/or token= may be specified to force the use of a particular
962 smard card reader or token if there is more than one available.
963 certid= and/or certlabel= may be specified to force the selec‐
964 tion of a particular certificate on the device. See the
965 pkinit_cert_match configuration option for more ways to select a
966 particular certificate to use for PKINIT.
967 ENV:envvar
969 envvar specifies the name of an environment variable which has
970 been set to a value conforming to one of the previous values.
971 For example, ENV:X509_PROXY, where environment variable
972 X509_PROXY has been set to FILE:/tmp/my_proxy.pem.
973 PKINIT krb5.conf options
975 pkinit_anchors
976 Specifies the location of trusted anchor (root) certificates
977 which the client trusts to sign KDC certificates. This option
978 may be specified multiple times. These values from the config
979 file are not used if the user specifies X509_anchors on the com‐
980 mand line.
981 pkinit_cert_match
983 Specifies matching rules that the client certificate must match
984 before it is used to attempt PKINIT authentication. If a user
985 has multiple certificates available (on a smart card, or via
986 other media), there must be exactly one certificate chosen be‐
987 fore attempting PKINIT authentication. This option may be spec‐
988 ified multiple times. All the available certificates are
989 checked against each rule in order until there is a match of ex‐
990 actly one certificate.
991 The Subject and Issuer comparison strings are the RFC 2253
993 string representations from the certificate Subject DN and Is‐
994 suer DN values.
995 The syntax of the matching rules is:
997 [relation-operator]component-rule ...
998 where:
1000 relation-operator
1002 can be either &&, meaning all component rules must match,
1003 or ||, meaning only one component rule must match. The
1004 default is &&.
1005 component-rule
1007 can be one of the following. Note that there is no punc‐
1008 tuation or whitespace between component rules.
1009 <SUBJECT>regular-expression
1010 <ISSUER>regular-expression
1011 <SAN>regular-expression
1012 <EKU>extended-key-usage-list
1013 <KU>key-usage-list
1014 extended-key-usage-list is a comma-separated list of re‐
1017 quired Extended Key Usage values. All values in the list
1018 must be present in the certificate. Extended Key Usage
1019 values can be:
1020 • pkinit
1022 • msScLogin
1024 • clientAuth
1026 • emailProtection
1028 key-usage-list is a comma-separated list of required Key
1030 Usage values. All values in the list must be present in
1031 the certificate. Key Usage values can be:
1032 • digitalSignature
1034 • keyEncipherment
1036 Examples:
1038 pkinit_cert_match = ||<SUBJECT>.*DoE.*<SAN>.*@EXAMPLE.COM
1040 pkinit_cert_match = &&<EKU>msScLogin,clientAuth<ISSUER>.*DoE.*
1041 pkinit_cert_match = <EKU>msScLogin,clientAuth<KU>digitalSignature
1042 pkinit_eku_checking
1044 This option specifies what Extended Key Usage value the KDC cer‐
1045 tificate presented to the client must contain. (Note that if
1046 the KDC certificate has the pkinit SubjectAlternativeName en‐
1047 coded as the Kerberos TGS name, EKU checking is not necessary
1048 since the issuing CA has certified this as a KDC certificate.)
1049 The values recognized in the krb5.conf file are:
1050 kpKDC This is the default value and specifies that the KDC must
1052 have the id-pkinit-KPKdc EKU as defined in RFC 4556.
1053 kpServerAuth
1055 If kpServerAuth is specified, a KDC certificate with the
1056 id-kp-serverAuth EKU will be accepted. This key usage
1057 value is used in most commercially issued server certifi‐
1058 cates.
1059 none If none is specified, then the KDC certificate will not
1061 be checked to verify it has an acceptable EKU. The use
1062 of this option is not recommended.
1063 pkinit_dh_min_bits
1065 Specifies the size of the Diffie-Hellman key the client will at‐
1066 tempt to use. The acceptable values are 1024, 2048, and 4096.
1067 The default is 2048.
1068 pkinit_identities
1070 Specifies the location(s) to be used to find the user's X.509
1071 identity information. If this option is specified multiple
1072 times, each value is attempted in order until certificates are
1073 found. Note that these values are not used if the user speci‐
1074 fies X509_user_identity on the command line.
1075 pkinit_kdc_hostname
1077 The presence of this option indicates that the client is willing
1078 to accept a KDC certificate with a dNSName SAN (Subject Alterna‐
1079 tive Name) rather than requiring the id-pkinit-san as defined in
1080 RFC 4556. This option may be specified multiple times. Its
1081 value should contain the acceptable hostname for the KDC (as
1082 contained in its certificate).
1083 pkinit_pool
1085 Specifies the location of intermediate certificates which may be
1086 used by the client to complete the trust chain between a KDC
1087 certificate and a trusted anchor. This option may be specified
1088 multiple times.
1089 pkinit_require_crl_checking
1091 The default certificate verification process will always check
1092 the available revocation information to see if a certificate has
1093 been revoked. If a match is found for the certificate in a CRL,
1094 verification fails. If the certificate being verified is not
1095 listed in a CRL, or there is no CRL present for its issuing CA,
1096 and pkinit_require_crl_checking is false, then verification suc‐
1097 ceeds.
1098 However, if pkinit_require_crl_checking is true and there is no
1100 CRL information available for the issuing CA, then verification
1101 fails.
1102 pkinit_require_crl_checking should be set to true if the policy
1104 is such that up-to-date CRLs must be present for every CA.
1105 pkinit_revoke
1107 Specifies the location of Certificate Revocation List (CRL) in‐
1108 formation to be used by the client when verifying the validity
1109 of the KDC certificate presented. This option may be specified
1110 multiple times.
1111
1113 Starting with release 1.11, several variables, such as de‐
1114 fault_keytab_name, allow parameters to be expanded. Valid parameters
1115 are:
1116 ┌──────────────────┬────────────────────────────┐
1118 │%{TEMP} │ Temporary directory │
1119 ├──────────────────┼────────────────────────────┤
1120 │%{uid} │ Unix real UID or Windows │
1121 │ │ SID │
1122 ├──────────────────┼────────────────────────────┤
1123 │%{euid} │ Unix effective user ID or │
1124 │ │ Windows SID │
1125 ├──────────────────┼────────────────────────────┤
1126 │%{USERID} │ Same as %{uid} │
1127 ├──────────────────┼────────────────────────────┤
1128 │%{null} │ Empty string │
1129 ├──────────────────┼────────────────────────────┤
1130 │%{LIBDIR} │ Installation library di‐ │
1131 │ │ rectory │
1132 ├──────────────────┼────────────────────────────┤
1133 │%{BINDIR} │ Installation binary direc‐ │
1134 │ │ tory │
1135 ├──────────────────┼────────────────────────────┤
1136 │%{SBINDIR} │ Installation admin binary │
1137 │ │ directory │
1138 ├──────────────────┼────────────────────────────┤
1139 │%{username} │ (Unix) Username of effec‐ │
1140 │ │ tive user ID │
1141 ├──────────────────┼────────────────────────────┤
1142 │%{APPDATA} │ (Windows) Roaming applica‐ │
1143 │ │ tion data for current user │
1144 ├──────────────────┼────────────────────────────┤
1145 │%{COMMON_APPDATA} │ (Windows) Application data │
1146 │ │ for all users │
1147 ├──────────────────┼────────────────────────────┤
1148 │%{LOCAL_APPDATA} │ (Windows) Local applica‐ │
1149 │ │ tion data for current user │
1150 └──────────────────┴────────────────────────────┘
1151 │%{SYSTEM} │ (Windows) Windows system │
1154 │ │ folder │
1155 ├──────────────────┼────────────────────────────┤
1156 │%{WINDOWS} │ (Windows) Windows folder │
1157 ├──────────────────┼────────────────────────────┤
1158 │%{USERCONFIG} │ (Windows) Per-user MIT │
1159 │ │ krb5 config file directory │
1160 ├──────────────────┼────────────────────────────┤
1161 │%{COMMONCONFIG} │ (Windows) Common MIT krb5 │
1162 │ │ config file directory │
1163 └──────────────────┴────────────────────────────┘
1164
1166 Here is an example of a generic krb5.conf file:
1167 [libdefaults]
1169 default_realm = ATHENA.MIT.EDU
1170 dns_lookup_kdc = true
1171 dns_lookup_realm = false
1172 [realms]
1174 ATHENA.MIT.EDU = {
1175 kdc = kerberos.mit.edu
1176 kdc = kerberos-1.mit.edu
1177 kdc = kerberos-2.mit.edu
1178 admin_server = kerberos.mit.edu
1179 primary_kdc = kerberos.mit.edu
1180 }
1181 EXAMPLE.COM = {
1182 kdc = kerberos.example.com
1183 kdc = kerberos-1.example.com
1184 admin_server = kerberos.example.com
1185 }
1186 [domain_realm]
1188 mit.edu = ATHENA.MIT.EDU
1189 [capaths]
1191 ATHENA.MIT.EDU = {
1192 EXAMPLE.COM = .
1193 }
1194 EXAMPLE.COM = {
1195 ATHENA.MIT.EDU = .
1196 }
1197
1199 /etc/krb5.conf
1200
1202 syslog(3)
1203
1205 MIT
1206
1208 1985-2021, MIT
12091.19.1 KRB5.CONF(5)