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
23 ignored as comments. Sections are headed by the section name, in
24 square brackets. Each section may contain zero or more relations, of
25 the form:
26 foo = bar
28 or:
30 fubar = {
32 foo = bar
33 baz = quux
34 }
35 Placing a '*' at the end of a line indicates that this is the final
37 value for the tag. This means that neither the remainder of this con‐
38 figuration file nor any other configuration file will be checked for
39 any other values for this tag.
40 For example, if you have the following lines:
42 foo = bar*
44 foo = baz
45 then the second value of foo (baz) would never be read.
47 The krb5.conf file can include other files using either of the follow‐
49 ing directives at the beginning of a line:
50 include FILENAME
52 includedir DIRNAME
53 FILENAME or DIRNAME should be an absolute path. The named file or
55 directory must exist and be readable. Including a directory includes
56 all files within the directory whose names consist solely of alphanu‐
57 meric characters, dashes, or underscores. Starting in release 1.15,
58 files with names ending in ".conf" are also included, unless the name
59 begins with ".". Included profile files are syntactically independent
60 of their parents, so each included file must begin with a section
61 header. Starting in release 1.17, files are read in alphanumeric
62 order; in previous releases, they may be read in any order.
63 The krb5.conf file can specify that configuration should be obtained
65 from a loadable module, rather than the file itself, using the follow‐
66 ing directive at the beginning of a line before any section headers:
67 module MODULEPATH:RESIDUAL
69 MODULEPATH may be relative to the library path of the krb5 installa‐
71 tion, or it may be an absolute path. RESIDUAL is provided to the mod‐
72 ule at initialization time. If krb5.conf uses a module directive,
73 kdc.conf(5) should also use one if it exists.
74
76 The krb5.conf file may contain the following sections:
77 ┌───────────────┬────────────────────────────┐
79 │[libdefaults] │ Settings used by the Ker‐ │
80 │ │ beros V5 library │
81 ├───────────────┼────────────────────────────┤
82 │[realms] │ Realm-specific contact │
83 │ │ information and settings │
84 ├───────────────┼────────────────────────────┤
85 │[domain_realm] │ Maps server hostnames to │
86 │ │ Kerberos realms │
87 ├───────────────┼────────────────────────────┤
88 │[capaths] │ Authentication paths for │
89 │ │ non-hierarchical │
90 │ │ cross-realm │
91 ├───────────────┼────────────────────────────┤
92 │[appdefaults] │ Settings used by some Ker‐ │
93 │ │ beros V5 applications │
94 ├───────────────┼────────────────────────────┤
95 │[plugins] │ Controls plugin module │
96 │ │ registration │
97 └───────────────┴────────────────────────────┘
98 Additionally, krb5.conf may include any of the relations described in
100 kdc.conf(5), but it is not a recommended practice.
101 [libdefaults]
103 The libdefaults section may contain any of the following relations:
104 allow_weak_crypto
106 If this flag is set to false, then weak encryption types (as
107 noted in Encryption_types in kdc.conf(5)) will be filtered out
108 of the lists default_tgs_enctypes, default_tkt_enctypes, and
109 permitted_enctypes. The default value for this tag is false,
110 which may cause authentication failures in existing Kerberos in‐
111 frastructures that do not support strong crypto. Users in
112 affected environments should set this tag to true until their
113 infrastructure adopts stronger ciphers.
114 ap_req_checksum_type
116 An integer which specifies the type of AP-REQ checksum to use in
117 authenticators. This variable should be unset so the appropri‐
118 ate checksum for the encryption key in use will be used. This
119 can be set if backward compatibility requires a specific check‐
120 sum type. See the kdc_req_checksum_type configuration option
121 for the possible values and their meanings.
122 canonicalize
124 If this flag is set to true, initial ticket requests to the KDC
125 will request canonicalization of the client principal name, and
126 answers with different client principals than the requested
127 principal will be accepted. The default value is false.
128 ccache_type
130 This parameter determines the format of credential cache types
131 created by kinit(1) or other programs. The default value is 4,
132 which represents the most current format. Smaller values can be
133 used for compatibility with very old implementations of Kerberos
134 which interact with credential caches on the same host.
135 clockskew
137 Sets the maximum allowable amount of clockskew in seconds that
138 the library will tolerate before assuming that a Kerberos mes‐
139 sage is invalid. The default value is 300 seconds, or five min‐
140 utes.
141 The clockskew setting is also used when evaluating ticket start
143 and expiration times. For example, tickets that have reached
144 their expiration time can still be used (and renewed if they are
145 renewable tickets) if they have been expired for a shorter dura‐
146 tion than the clockskew setting.
147 default_ccache_name
149 This relation specifies the name of the default credential
150 cache. The default is FILE:/tmp/krb5cc_%{uid}. This relation
151 is subject to parameter expansion (see below). New in release
152 1.11.
153 default_client_keytab_name
155 This relation specifies the name of the default keytab for
156 obtaining client credentials. The default is FILE:/var/ker‐
157 beros/krb5/user/%{euid}/client.keytab. This relation is subject
158 to parameter expansion (see below). New in release 1.11.
159 default_keytab_name
161 This relation specifies the default keytab name to be used by
162 application servers such as sshd. The default is
163 FILE:/etc/krb5.keytab. This relation is subject to parameter
164 expansion (see below).
165 default_realm
167 Identifies the default Kerberos realm for the client. Set its
168 value to your Kerberos realm. If this value is not set, then a
169 realm must be specified with every Kerberos principal when
170 invoking programs such as kinit(1).
171 default_tgs_enctypes
173 Identifies the supported list of session key encryption types
174 that the client should request when making a TGS-REQ, in order
175 of preference from highest to lowest. The list may be delimited
176 with commas or whitespace. See Encryption_types in kdc.conf(5)
177 for a list of the accepted values for this tag. The default
178 value is aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
179 aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128
180 des3-cbc-sha1 arcfour-hmac-md5 camellia256-cts-cmac camel‐
181 lia128-cts-cmac des-cbc-crc des-cbc-md5 des-cbc-md4, but sin‐
182 gle-DES encryption types will be implicitly removed from this
183 list if the value of allow_weak_crypto is false.
184 Do not set this unless required for specific backward compati‐
186 bility purposes; stale values of this setting can prevent
187 clients from taking advantage of new stronger enctypes when the
188 libraries are upgraded.
189 default_tkt_enctypes
191 Identifies the supported list of session key encryption types
192 that the client should request when making an AS-REQ, in order
193 of preference from highest to lowest. The format is the same as
194 for default_tgs_enctypes. The default value for this tag is
195 aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
196 aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128
197 des3-cbc-sha1 arcfour-hmac-md5 camellia256-cts-cmac camel‐
198 lia128-cts-cmac des-cbc-crc des-cbc-md5 des-cbc-md4, but sin‐
199 gle-DES encryption types will be implicitly removed from this
200 list if the value of allow_weak_crypto is false.
201 Do not set this unless required for specific backward compati‐
203 bility purposes; stale values of this setting can prevent
204 clients from taking advantage of new stronger enctypes when the
205 libraries are upgraded.
206 dns_canonicalize_hostname
208 Indicate whether name lookups will be used to canonicalize host‐
209 names for use in service principal names. Setting this flag to
210 false can improve security by reducing reliance on DNS, but
211 means that short hostnames will not be canonicalized to
212 fully-qualified hostnames. The default value is true.
213 dns_lookup_kdc
215 Indicate whether DNS SRV records should be used to locate the
216 KDCs and other servers for a realm, if they are not listed in
217 the krb5.conf information for the realm. (Note that the
218 admin_server entry must be in the krb5.conf realm information in
219 order to contact kadmind, because the DNS implementation for
220 kadmin is incomplete.)
221 Enabling this option does open up a type of denial-of-service
223 attack, if someone spoofs the DNS records and redirects you to
224 another server. However, it's no worse than a denial of ser‐
225 vice, because that fake KDC will be unable to decode anything
226 you send it (besides the initial ticket request, which has no
227 encrypted data), and anything the fake KDC sends will not be
228 trusted without verification using some secret that it won't
229 know.
230 dns_uri_lookup
232 Indicate whether DNS URI records should be used to locate the
233 KDCs and other servers for a realm, if they are not listed in
234 the krb5.conf information for the realm. SRV records are used
235 as a fallback if no URI records were found. The default value
236 is true. New in release 1.15.
237 err_fmt
239 This relation allows for custom error message formatting. If a
240 value is set, error messages will be formatted by substituting a
241 normal error message for %M and an error code for %C in the
242 value.
243 extra_addresses
245 This allows a computer to use multiple local addresses, in order
246 to allow Kerberos to work in a network that uses NATs while
247 still using address-restricted tickets. The addresses should be
248 in a comma-separated list. This option has no effect if noad‐
249 dresses is true.
250 forwardable
252 If this flag is true, initial tickets will be forwardable by
253 default, if allowed by the KDC. The default value is false.
254 ignore_acceptor_hostname
256 When accepting GSSAPI or krb5 security contexts for host-based
257 service principals, ignore any hostname passed by the calling
258 application, and allow clients to authenticate to any service
259 principal in the keytab matching the service name and realm name
260 (if given). This option can improve the administrative flexi‐
261 bility of server applications on multihomed hosts, but could
262 compromise the security of virtual hosting environments. The
263 default value is false. New in release 1.10.
264 k5login_authoritative
266 If this flag is true, principals must be listed in a local
267 user's k5login file to be granted login access, if a .k5login(5)
268 file exists. If this flag is false, a principal may still be
269 granted login access through other mechanisms even if a k5login
270 file exists but does not list the principal. The default value
271 is true.
272 k5login_directory
274 If set, the library will look for a local user's k5login file
275 within the named directory, with a filename corresponding to the
276 local username. If not set, the library will look for k5login
277 files in the user's home directory, with the filename .k5login.
278 For security reasons, .k5login files must be owned by the local
279 user or by root.
280 kcm_mach_service
282 On macOS only, determines the name of the bootstrap service used
283 to contact the KCM daemon for the KCM credential cache type. If
284 the value is -, Mach RPC will not be used to contact the KCM
285 daemon. The default value is org.h5l.kcm.
286 kcm_socket
288 Determines the path to the Unix domain socket used to access the
289 KCM daemon for the KCM credential cache type. If the value is
290 -, Unix domain sockets will not be used to contact the KCM dae‐
291 mon. The default value is /var/run/.heim_org.h5l.kcm-socket.
292 kdc_default_options
294 Default KDC options (Xored for multiple values) when requesting
295 initial tickets. By default it is set to 0x00000010
296 (KDC_OPT_RENEWABLE_OK).
297 kdc_timesync
299 Accepted values for this relation are 1 or 0. If it is nonzero,
300 client machines will compute the difference between their time
301 and the time returned by the KDC in the timestamps in the tick‐
302 ets and use this value to correct for an inaccurate system clock
303 when requesting service tickets or authenticating to services.
304 This corrective factor is only used by the Kerberos library; it
305 is not used to change the system clock. The default value is 1.
306 kdc_req_checksum_type
308 An integer which specifies the type of checksum to use for the
309 KDC requests, for compatibility with very old KDC implementa‐
310 tions. This value is only used for DES keys; other keys use the
311 preferred checksum type for those keys.
312 The possible values and their meanings are as follows.
314 ┌─────┬────────────────────────────┐
316 │1 │ CRC32 │
317 ├─────┼────────────────────────────┤
318 │2 │ RSA MD4 │
319 ├─────┼────────────────────────────┤
320 │3 │ RSA MD4 DES │
321 ├─────┼────────────────────────────┤
322 │4 │ DES CBC │
323 ├─────┼────────────────────────────┤
324 │7 │ RSA MD5 │
325 ├─────┼────────────────────────────┤
326 │8 │ RSA MD5 DES │
327 ├─────┼────────────────────────────┤
328 │9 │ NIST SHA │
329 └─────┴────────────────────────────┘
330 │12 │ HMAC SHA1 DES3 │
332 ├─────┼────────────────────────────┤
333 │-138 │ Microsoft MD5 HMAC check‐ │
334 │ │ sum type │
335 └─────┴────────────────────────────┘
336 noaddresses
338 If this flag is true, requests for initial tickets will not be
339 made with address restrictions set, allowing the tickets to be
340 used across NATs. The default value is true.
341 permitted_enctypes
343 Identifies all encryption types that are permitted for use in
344 session key encryption. The default value for this tag is
345 aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
346 aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128
347 des3-cbc-sha1 arcfour-hmac-md5 camellia256-cts-cmac camel‐
348 lia128-cts-cmac des-cbc-crc des-cbc-md5 des-cbc-md4, but sin‐
349 gle-DES encryption types will be implicitly removed from this
350 list if the value of allow_weak_crypto is false.
351 plugin_base_dir
353 If set, determines the base directory where krb5 plugins are
354 located. The default value is the krb5/plugins subdirectory of
355 the krb5 library directory.
356 preferred_preauth_types
358 This allows you to set the preferred preauthentication types
359 which the client will attempt before others which may be adver‐
360 tised by a KDC. The default value for this setting is "17, 16,
361 15, 14", which forces libkrb5 to attempt to use PKINIT if it is
362 supported.
363 proxiable
365 If this flag is true, initial tickets will be proxiable by
366 default, if allowed by the KDC. The default value is false.
367 rdns If this flag is true, reverse name lookup will be used in addi‐
369 tion to forward name lookup to canonicalizing hostnames for use
370 in service principal names. If dns_canonicalize_hostname is set
371 to false, this flag has no effect. The default value is true.
372 realm_try_domains
374 Indicate whether a host's domain components should be used to
375 determine the Kerberos realm of the host. The value of this
376 variable is an integer: -1 means not to search, 0 means to try
377 the host's domain itself, 1 means to also try the domain's imme‐
378 diate parent, and so forth. The library's usual mechanism for
379 locating Kerberos realms is used to determine whether a domain
380 is a valid realm, which may involve consulting DNS if
381 dns_lookup_kdc is set. The default is not to search domain com‐
382 ponents.
383 renew_lifetime
385 (duration string.) Sets the default renewable lifetime for ini‐
386 tial ticket requests. The default value is 0.
387 safe_checksum_type
389 An integer which specifies the type of checksum to use for the
390 KRB-SAFE requests. By default it is set to 8 (RSA MD5 DES).
391 For compatibility with applications linked against DCE version
392 1.1 or earlier Kerberos libraries, use a value of 3 to use the
393 RSA MD4 DES instead. This field is ignored when its value is
394 incompatible with the session key type. See the kdc_req_check‐
395 sum_type configuration option for the possible values and their
396 meanings.
397 spake_preauth_groups
399 A whitespace or comma-separated list of words which specifies
400 the groups allowed for SPAKE preauthentication. The possible
401 values are:
402 ┌─────────────┬────────────────────────────┐
404 │edwards25519 │ Edwards25519 curve (RFC │
405 │ │ 7748) │
406 ├─────────────┼────────────────────────────┤
407 │P-256 │ NIST P-256 curve (RFC │
408 │ │ 5480) │
409 ├─────────────┼────────────────────────────┤
410 │P-384 │ NIST P-384 curve (RFC │
411 │ │ 5480) │
412 ├─────────────┼────────────────────────────┤
413 │P-521 │ NIST P-521 curve (RFC │
414 │ │ 5480) │
415 └─────────────┴────────────────────────────┘
416 The default value for the client is edwards25519. The default
418 value for the KDC is empty. New in release 1.17.
419 ticket_lifetime
421 (duration string.) Sets the default lifetime for initial ticket
422 requests. The default value is 1 day.
423 udp_preference_limit
425 When sending a message to the KDC, the library will try using
426 TCP before UDP if the size of the message is above udp_prefer‐
427 ence_limit. If the message is smaller than udp_prefer‐
428 ence_limit, then UDP will be tried before TCP. Regardless of
429 the size, both protocols will be tried if the first attempt
430 fails.
431 verify_ap_req_nofail
433 If this flag is true, then an attempt to verify initial creden‐
434 tials will fail if the client machine does not have a keytab.
435 The default value is false.
436 [realms]
438 Each tag in the [realms] section of the file is the name of a Kerberos
439 realm. The value of the tag is a subsection with relations that define
440 the properties of that particular realm. For each realm, the following
441 tags may be specified in the realm's subsection:
442 admin_server
444 Identifies the host where the administration server is running.
445 Typically, this is the master Kerberos server. This tag must be
446 given a value in order to communicate with the kadmind(8) server
447 for the realm.
448 auth_to_local
450 This tag allows you to set a general rule for mapping principal
451 names to local user names. It will be used if there is not an
452 explicit mapping for the principal name that is being trans‐
453 lated. The possible values are:
454 RULE:exp
456 The local name will be formulated from exp.
457 The format for exp is [n:string](regexp)s/pat‐
459 tern/replacement/g. The integer n indicates how many
460 components the target principal should have. If this
461 matches, then a string will be formed from string, sub‐
462 stituting the realm of the principal for $0 and the n'th
463 component of the principal for $n (e.g., if the principal
464 was johndoe/admin then [2:$2$1foo] would result in the
465 string adminjohndoefoo). If this string matches regexp,
466 then the s//[g] substitution command will be run over the
467 string. The optional g will cause the substitution to be
468 global over the string, instead of replacing only the
469 first match in the string.
470 DEFAULT
472 The principal name will be used as the local user name.
473 If the principal has more than one component or is not in
474 the default realm, this rule is not applicable and the
475 conversion will fail.
476 For example:
478 [realms]
480 ATHENA.MIT.EDU = {
481 auth_to_local = RULE:[2:$1](johndoe)s/^.*$/guest/
482 auth_to_local = RULE:[2:$1;$2](^.*;admin$)s/;admin$//
483 auth_to_local = RULE:[2:$2](^.*;root)s/^.*$/root/
484 auto_to_local = DEFAULT
485 }
486 would result in any principal without root or admin as the sec‐
488 ond component to be translated with the default rule. A princi‐
489 pal with a second component of admin will become its first com‐
490 ponent. root will be used as the local name for any principal
491 with a second component of root. The exception to these two
492 rules are any principals johndoe/*, which will always get the
493 local name guest.
494 auth_to_local_names
496 This subsection allows you to set explicit mappings from princi‐
497 pal names to local user names. The tag is the mapping name, and
498 the value is the corresponding local user name.
499 default_domain
501 This tag specifies the domain used to expand hostnames when
502 translating Kerberos 4 service principals to Kerberos 5 princi‐
503 pals (for example, when converting rcmd.hostname to host/host‐
504 name.domain).
505 disable_encrypted_timestamp
507 If this flag is true, the client will not perform encrypted
508 timestamp preauthentication if requested by the KDC. Setting
509 this flag can help to prevent dictionary attacks by active
510 attackers, if the realm's KDCs support SPAKE preauthentication
511 or if initial authentication always uses another mechanism or
512 always uses FAST. This flag persists across client referrals
513 during initial authentication. This flag does not prevent the
514 KDC from offering encrypted timestamp. New in release 1.17.
515 http_anchors
517 When KDCs and kpasswd servers are accessed through HTTPS prox‐
518 ies, this tag can be used to specify the location of the CA cer‐
519 tificate which should be trusted to issue the certificate for a
520 proxy server. If left unspecified, the system-wide default set
521 of CA certificates is used.
522 The syntax for values is similar to that of values for the
524 pkinit_anchors tag:
525 FILE: filename
527 filename is assumed to be the name of an OpenSSL-style ca-bundle
529 file.
530 DIR: dirname
532 dirname is assumed to be an directory which contains CA certifi‐
534 cates. All files in the directory will be examined; if they
535 contain certificates (in PEM format), they will be used.
536 ENV: envvar
538 envvar specifies the name of an environment variable which has
540 been set to a value conforming to one of the previous values.
541 For example, ENV:X509_PROXY_CA, where environment variable
542 X509_PROXY_CA has been set to FILE:/tmp/my_proxy.pem.
543 kdc The name or address of a host running a KDC for that realm. An
545 optional port number, separated from the hostname by a colon,
546 may be included. If the name or address contains colons (for
547 example, if it is an IPv6 address), enclose it in square brack‐
548 ets to distinguish the colon from a port separator. For your
549 computer to be able to communicate with the KDC for each realm,
550 this tag must be given a value in each realm subsection in the
551 configuration file, or there must be DNS SRV records specifying
552 the KDCs.
553 kpasswd_server
555 Points to the server where all the password changes are per‐
556 formed. If there is no such entry, the port 464 on the
557 admin_server host will be tried.
558 master_kdc
560 Identifies the master KDC(s). Currently, this tag is used in
561 only one case: If an attempt to get credentials fails because of
562 an invalid password, the client software will attempt to contact
563 the master KDC, in case the user's password has just been
564 changed, and the updated database has not been propagated to the
565 slave servers yet.
566 v4_instance_convert
568 This subsection allows the administrator to configure exceptions
569 to the default_domain mapping rule. It contains V4 instances
570 (the tag name) which should be translated to some specific host‐
571 name (the tag value) as the second component in a Kerberos V5
572 principal name.
573 v4_realm
575 This relation is used by the krb524 library routines when con‐
576 verting a V5 principal name to a V4 principal name. It is used
577 when the V4 realm name and the V5 realm name are not the same,
578 but still share the same principal names and passwords. The tag
579 value is the Kerberos V4 realm name.
580 [domain_realm]
582 The [domain_realm] section provides a translation from a domain name or
583 hostname to a Kerberos realm name. The tag name can be a host name or
584 domain name, where domain names are indicated by a prefix of a period
585 (.). The value of the relation is the Kerberos realm name for that
586 particular host or domain. A host name relation implicitly provides
587 the corresponding domain name relation, unless an explicit domain name
588 relation is provided. The Kerberos realm may be identified either in
589 the realms section or using DNS SRV records. Host names and domain
590 names should be in lower case. For example:
591 [domain_realm]
593 crash.mit.edu = TEST.ATHENA.MIT.EDU
594 .dev.mit.edu = TEST.ATHENA.MIT.EDU
595 mit.edu = ATHENA.MIT.EDU
596 maps the host with the name crash.mit.edu into the TEST.ATHENA.MIT.EDU
598 realm. The second entry maps all hosts under the domain dev.mit.edu
599 into the TEST.ATHENA.MIT.EDU realm, but not the host with the name
600 dev.mit.edu. That host is matched by the third entry, which maps the
601 host mit.edu and all hosts under the domain mit.edu that do not match a
602 preceding rule into the realm ATHENA.MIT.EDU.
603 If no translation entry applies to a hostname used for a service prin‐
605 cipal for a service ticket request, the library will try to get a
606 referral to the appropriate realm from the client realm's KDC. If that
607 does not succeed, the host's realm is considered to be the hostname's
608 domain portion converted to uppercase, unless the realm_try_domains
609 setting in [libdefaults] causes a different parent domain to be used.
610 [capaths]
612 In order to perform direct (non-hierarchical) cross-realm authentica‐
613 tion, configuration is needed to determine the authentication paths
614 between realms.
615 A client will use this section to find the authentication path between
617 its realm and the realm of the server. The server will use this sec‐
618 tion to verify the authentication path used by the client, by checking
619 the transited field of the received ticket.
620 There is a tag for each participating client realm, and each tag has
622 subtags for each of the server realms. The value of the subtags is an
623 intermediate realm which may participate in the cross-realm authentica‐
624 tion. The subtags may be repeated if there is more then one intermedi‐
625 ate realm. A value of "." means that the two realms share keys
626 directly, and no intermediate realms should be allowed to participate.
627 Only those entries which will be needed on the client or the server
629 need to be present. A client needs a tag for its local realm with sub‐
630 tags for all the realms of servers it will need to authenticate to. A
631 server needs a tag for each realm of the clients it will serve, with a
632 subtag of the server realm.
633 For example, ANL.GOV, PNL.GOV, and NERSC.GOV all wish to use the ES.NET
635 realm as an intermediate realm. ANL has a sub realm of TEST.ANL.GOV
636 which will authenticate with NERSC.GOV but not PNL.GOV. The [capaths]
637 section for ANL.GOV systems would look like this:
638 [capaths]
640 ANL.GOV = {
641 TEST.ANL.GOV = .
642 PNL.GOV = ES.NET
643 NERSC.GOV = ES.NET
644 ES.NET = .
645 }
646 TEST.ANL.GOV = {
647 ANL.GOV = .
648 }
649 PNL.GOV = {
650 ANL.GOV = ES.NET
651 }
652 NERSC.GOV = {
653 ANL.GOV = ES.NET
654 }
655 ES.NET = {
656 ANL.GOV = .
657 }
658 The [capaths] section of the configuration file used on NERSC.GOV sys‐
660 tems would look like this:
661 [capaths]
663 NERSC.GOV = {
664 ANL.GOV = ES.NET
665 TEST.ANL.GOV = ES.NET
666 TEST.ANL.GOV = ANL.GOV
667 PNL.GOV = ES.NET
668 ES.NET = .
669 }
670 ANL.GOV = {
671 NERSC.GOV = ES.NET
672 }
673 PNL.GOV = {
674 NERSC.GOV = ES.NET
675 }
676 ES.NET = {
677 NERSC.GOV = .
678 }
679 TEST.ANL.GOV = {
680 NERSC.GOV = ANL.GOV
681 NERSC.GOV = ES.NET
682 }
683 When a subtag is used more than once within a tag, clients will use the
685 order of values to determine the path. The order of values is not
686 important to servers.
687 [appdefaults]
689 Each tag in the [appdefaults] section names a Kerberos V5 application
690 or an option that is used by some Kerberos V5 application[s]. The
691 value of the tag defines the default behaviors for that application.
692 For example:
694 [appdefaults]
696 telnet = {
697 ATHENA.MIT.EDU = {
698 option1 = false
699 }
700 }
701 telnet = {
702 option1 = true
703 option2 = true
704 }
705 ATHENA.MIT.EDU = {
706 option2 = false
707 }
708 option2 = true
709 The above four ways of specifying the value of an option are shown in
711 order of decreasing precedence. In this example, if telnet is running
712 in the realm EXAMPLE.COM, it should, by default, have option1 and
713 option2 set to true. However, a telnet program in the realm
714 ATHENA.MIT.EDU should have option1 set to false and option2 set to
715 true. Any other programs in ATHENA.MIT.EDU should have option2 set to
716 false by default. Any programs running in other realms should have
717 option2 set to true.
718 The list of specifiable options for each application may be found in
720 that application's man pages. The application defaults specified here
721 are overridden by those specified in the realms section.
722 [plugins]
724 · pwqual interface
725 · kadm5_hook interface
727 · clpreauth and kdcpreauth interfaces
729 Tags in the [plugins] section can be used to register dynamic plugin
731 modules and to turn modules on and off. Not every krb5 pluggable
732 interface uses the [plugins] section; the ones that do are documented
733 here.
734 New in release 1.9.
736 Each pluggable interface corresponds to a subsection of [plugins]. All
738 subsections support the same tags:
739 disable
741 This tag may have multiple values. If there are values for this
742 tag, then the named modules will be disabled for the pluggable
743 interface.
744 enable_only
746 This tag may have multiple values. If there are values for this
747 tag, then only the named modules will be enabled for the plug‐
748 gable interface.
749 module This tag may have multiple values. Each value is a string of
751 the form modulename:pathname, which causes the shared object
752 located at pathname to be registered as a dynamic module named
753 modulename for the pluggable interface. If pathname is not an
754 absolute path, it will be treated as relative to the plug‐
755 in_base_dir value from [libdefaults].
756 For pluggable interfaces where module order matters, modules registered
758 with a module tag normally come first, in the order they are regis‐
759 tered, followed by built-in modules in the order they are documented
760 below. If enable_only tags are used, then the order of those tags
761 overrides the normal module order.
762 The following subsections are currently supported within the [plugins]
764 section:
765 ccselect interface
767 The ccselect subsection controls modules for credential cache selection
768 within a cache collection. In addition to any registered dynamic mod‐
769 ules, the following built-in modules exist (and may be disabled with
770 the disable tag):
771 k5identity
773 Uses a .k5identity file in the user's home directory to select a
774 client principal
775 realm Uses the service realm to guess an appropriate cache from the
777 collection
778 hostname
780 If the service principal is host-based, uses the service host‐
781 name to guess an appropriate cache from the collection
782 pwqual interface
784 The pwqual subsection controls modules for the password quality inter‐
785 face, which is used to reject weak passwords when passwords are
786 changed. The following built-in modules exist for this interface:
787 dict Checks against the realm dictionary file
789 empty Rejects empty passwords
791 hesiod Checks against user information stored in Hesiod (only if Ker‐
793 beros was built with Hesiod support)
794 princ Checks against components of the principal name
796 kadm5_hook interface
798 The kadm5_hook interface provides plugins with information on principal
799 creation, modification, password changes and deletion. This interface
800 can be used to write a plugin to synchronize MIT Kerberos with another
801 database such as Active Directory. No plugins are built in for this
802 interface.
803 kadm5_auth interface
805 The kadm5_auth section (introduced in release 1.16) controls modules
806 for the kadmin authorization interface, which determines whether a
807 client principal is allowed to perform a kadmin operation. The follow‐
808 ing built-in modules exist for this interface:
809 acl This module reads the kadm5.acl(5) file, and authorizes opera‐
811 tions which are allowed according to the rules in the file.
812 self This module authorizes self-service operations including pass‐
814 word changes, creation of new random keys, fetching the client's
815 principal record or string attributes, and fetching the policy
816 record associated with the client principal.
817 clpreauth and kdcpreauth interfaces
819 The clpreauth and kdcpreauth interfaces allow plugin modules to provide
820 client and KDC preauthentication mechanisms. The following built-in
821 modules exist for these interfaces:
822 pkinit This module implements the PKINIT preauthentication mechanism.
824 encrypted_challenge
826 This module implements the encrypted challenge FAST factor.
827 encrypted_timestamp
829 This module implements the encrypted timestamp mechanism.
830 hostrealm interface
832 The hostrealm section (introduced in release 1.12) controls modules for
833 the host-to-realm interface, which affects the local mapping of host‐
834 names to realm names and the choice of default realm. The following
835 built-in modules exist for this interface:
836 profile
838 This module consults the [domain_realm] section of the profile
839 for authoritative host-to-realm mappings, and the default_realm
840 variable for the default realm.
841 dns This module looks for DNS records for fallback host-to-realm
843 mappings and the default realm. It only operates if the
844 dns_lookup_realm variable is set to true.
845 domain This module applies heuristics for fallback host-to-realm map‐
847 pings. It implements the realm_try_domains variable, and uses
848 the uppercased parent domain of the hostname if that does not
849 produce a result.
850 localauth interface
852 The localauth section (introduced in release 1.12) controls modules for
853 the local authorization interface, which affects the relationship
854 between Kerberos principals and local system accounts. The following
855 built-in modules exist for this interface:
856 default
858 This module implements the DEFAULT type for auth_to_local val‐
859 ues.
860 rule This module implements the RULE type for auth_to_local values.
862 names This module looks for an auth_to_local_names mapping for the
864 principal name.
865 auth_to_local
867 This module processes auth_to_local values in the default
868 realm's section, and applies the default method if no
869 auth_to_local values exist.
870 k5login
872 This module authorizes a principal to a local account according
873 to the account's .k5login(5) file.
874 an2ln This module authorizes a principal to a local account if the
876 principal name maps to the local account name.
877 certauth interface
879 The certauth section (introduced in release 1.16) controls modules for
880 the certificate authorization interface, which determines whether a
881 certificate is allowed to preauthenticate a user via PKINIT. The fol‐
882 lowing built-in modules exist for this interface:
883 pkinit_san
885 This module authorizes the certificate if it contains a PKINIT
886 Subject Alternative Name for the requested client principal, or
887 a Microsoft UPN SAN matching the principal if pkinit_allow_upn
888 is set to true for the realm.
889 pkinit_eku
891 This module rejects the certificate if it does not contain an
892 Extended Key Usage attribute consistent with the
893 pkinit_eku_checking value for the realm.
894 dbmatch
896 This module authorizes or rejects the certificate according to
897 whether it matches the pkinit_cert_match string attribute on the
898 client principal, if that attribute is present.
899
901 NOTE:
902 The following are PKINIT-specific options. These values may be
903 specified in [libdefaults] as global defaults, or within a
904 realm-specific subsection of [libdefaults], or may be specified as
905 realm-specific values in the [realms] section. A realm-specific
906 value overrides, not adds to, a generic [libdefaults] specification.
907 The search order is:
908 1. realm-specific subsection of [libdefaults]:
910 [libdefaults]
912 EXAMPLE.COM = {
913 pkinit_anchors = FILE:/usr/local/example.com.crt
914 }
915 2. realm-specific value in the [realms] section:
917 [realms]
919 OTHERREALM.ORG = {
920 pkinit_anchors = FILE:/usr/local/otherrealm.org.crt
921 }
922 3. generic value in the [libdefaults] section:
924 [libdefaults]
926 pkinit_anchors = DIR:/usr/local/generic_trusted_cas/
927 Specifying PKINIT identity information
929 The syntax for specifying Public Key identity, trust, and revocation
930 information for PKINIT is as follows:
931 FILE:filename[,keyfilename]
933 This option has context-specific behavior.
934 In pkinit_identity or pkinit_identities, filename specifies the
936 name of a PEM-format file containing the user's certificate. If
937 keyfilename is not specified, the user's private key is expected
938 to be in filename as well. Otherwise, keyfilename is the name
939 of the file containing the private key.
940 In pkinit_anchors or pkinit_pool, filename is assumed to be the
942 name of an OpenSSL-style ca-bundle file.
943 DIR:dirname
945 This option has context-specific behavior.
946 In pkinit_identity or pkinit_identities, dirname specifies a
948 directory with files named *.crt and *.key where the first part
949 of the file name is the same for matching pairs of certificate
950 and private key files. When a file with a name ending with .crt
951 is found, a matching file ending with .key is assumed to contain
952 the private key. If no such file is found, then the certificate
953 in the .crt is not used.
954 In pkinit_anchors or pkinit_pool, dirname is assumed to be an
956 OpenSSL-style hashed CA directory where each CA cert is stored
957 in a file named hash-of-ca-cert.#. This infrastructure is
958 encouraged, but all files in the directory will be examined and
959 if they contain certificates (in PEM format), they will be used.
960 In pkinit_revoke, dirname is assumed to be an OpenSSL-style
962 hashed CA directory where each revocation list is stored in a
963 file named hash-of-ca-cert.r#. This infrastructure is encour‐
964 aged, but all files in the directory will be examined and if
965 they contain a revocation list (in PEM format), they will be
966 used.
967 PKCS12:filename
969 filename is the name of a PKCS #12 format file, containing the
970 user's certificate and private key.
971 PKCS11:[module_name=]modname[:slotid=slot-id][:token=token-label][:cer‐
973 tid=cert-id][:certlabel=cert-label]
974 All keyword/values are optional. modname specifies the location
975 of a library implementing PKCS #11. If a value is encountered
976 with no keyword, it is assumed to be the modname. If no mod‐
977 ule-name is specified, the default is opensc-pkcs11.so. slotid=
978 and/or token= may be specified to force the use of a particular
979 smard card reader or token if there is more than one available.
980 certid= and/or certlabel= may be specified to force the selec‐
981 tion of a particular certificate on the device. See the
982 pkinit_cert_match configuration option for more ways to select a
983 particular certificate to use for PKINIT.
984 ENV:envvar
986 envvar specifies the name of an environment variable which has
987 been set to a value conforming to one of the previous values.
988 For example, ENV:X509_PROXY, where environment variable
989 X509_PROXY has been set to FILE:/tmp/my_proxy.pem.
990 PKINIT krb5.conf options
992 pkinit_anchors
993 Specifies the location of trusted anchor (root) certificates
994 which the client trusts to sign KDC certificates. This option
995 may be specified multiple times. These values from the config
996 file are not used if the user specifies X509_anchors on the com‐
997 mand line.
998 pkinit_cert_match
1000 Specifies matching rules that the client certificate must match
1001 before it is used to attempt PKINIT authentication. If a user
1002 has multiple certificates available (on a smart card, or via
1003 other media), there must be exactly one certificate chosen
1004 before attempting PKINIT authentication. This option may be
1005 specified multiple times. All the available certificates are
1006 checked against each rule in order until there is a match of
1007 exactly one certificate.
1008 The Subject and Issuer comparison strings are the RFC 2253
1010 string representations from the certificate Subject DN and
1011 Issuer DN values.
1012 The syntax of the matching rules is:
1014 [relation-operator]component-rule ...
1015 where:
1017 relation-operator
1019 can be either &&, meaning all component rules must match,
1020 or ||, meaning only one component rule must match. The
1021 default is &&.
1022 component-rule
1024 can be one of the following. Note that there is no punc‐
1025 tuation or whitespace between component rules.
1026 <SUBJECT>regular-expression
1027 <ISSUER>regular-expression
1028 <SAN>regular-expression
1029 <EKU>extended-key-usage-list
1030 <KU>key-usage-list
1031 extended-key-usage-list is a comma-separated list of
1034 required Extended Key Usage values. All values in the
1035 list must be present in the certificate. Extended Key
1036 Usage values can be:
1037 · pkinit
1039 · msScLogin
1041 · clientAuth
1043 · emailProtection
1045 key-usage-list is a comma-separated list of required Key
1047 Usage values. All values in the list must be present in
1048 the certificate. Key Usage values can be:
1049 · digitalSignature
1051 · keyEncipherment
1053 Examples:
1055 pkinit_cert_match = ||<SUBJECT>.*DoE.*<SAN>.*@EXAMPLE.COM
1057 pkinit_cert_match = &&<EKU>msScLogin,clientAuth<ISSUER>.*DoE.*
1058 pkinit_cert_match = <EKU>msScLogin,clientAuth<KU>digitalSignature
1059 pkinit_eku_checking
1061 This option specifies what Extended Key Usage value the KDC cer‐
1062 tificate presented to the client must contain. (Note that if
1063 the KDC certificate has the pkinit SubjectAlternativeName
1064 encoded as the Kerberos TGS name, EKU checking is not necessary
1065 since the issuing CA has certified this as a KDC certificate.)
1066 The values recognized in the krb5.conf file are:
1067 kpKDC This is the default value and specifies that the KDC must
1069 have the id-pkinit-KPKdc EKU as defined in RFC 4556.
1070 kpServerAuth
1072 If kpServerAuth is specified, a KDC certificate with the
1073 id-kp-serverAuth EKU will be accepted. This key usage
1074 value is used in most commercially issued server certifi‐
1075 cates.
1076 none If none is specified, then the KDC certificate will not
1078 be checked to verify it has an acceptable EKU. The use
1079 of this option is not recommended.
1080 pkinit_dh_min_bits
1082 Specifies the size of the Diffie-Hellman key the client will
1083 attempt to use. The acceptable values are 1024, 2048, and 4096.
1084 The default is 2048.
1085 pkinit_identities
1087 Specifies the location(s) to be used to find the user's X.509
1088 identity information. This option may be specified multiple
1089 times. Each value is attempted in order until identity informa‐
1090 tion is found and authentication is attempted. Note that these
1091 values are not used if the user specifies X509_user_identity on
1092 the command line.
1093 pkinit_kdc_hostname
1095 The presense of this option indicates that the client is willing
1096 to accept a KDC certificate with a dNSName SAN (Subject Alterna‐
1097 tive Name) rather than requiring the id-pkinit-san as defined in
1098 RFC 4556. This option may be specified multiple times. Its
1099 value should contain the acceptable hostname for the KDC (as
1100 contained in its certificate).
1101 pkinit_pool
1103 Specifies the location of intermediate certificates which may be
1104 used by the client to complete the trust chain between a KDC
1105 certificate and a trusted anchor. This option may be specified
1106 multiple times.
1107 pkinit_require_crl_checking
1109 The default certificate verification process will always check
1110 the available revocation information to see if a certificate has
1111 been revoked. If a match is found for the certificate in a CRL,
1112 verification fails. If the certificate being verified is not
1113 listed in a CRL, or there is no CRL present for its issuing CA,
1114 and pkinit_require_crl_checking is false, then verification suc‐
1115 ceeds.
1116 However, if pkinit_require_crl_checking is true and there is no
1118 CRL information available for the issuing CA, then verification
1119 fails.
1120 pkinit_require_crl_checking should be set to true if the policy
1122 is such that up-to-date CRLs must be present for every CA.
1123 pkinit_revoke
1125 Specifies the location of Certificate Revocation List (CRL)
1126 information to be used by the client when verifying the validity
1127 of the KDC certificate presented. This option may be specified
1128 multiple times.
1129
1131 Starting with release 1.11, several variables, such as
1132 default_keytab_name, allow parameters to be expanded. Valid parameters
1133 are:
1134 ┌──────────────────┬────────────────────────────┐
1136 │%{TEMP} │ Temporary directory │
1137 ├──────────────────┼────────────────────────────┤
1138 │%{uid} │ Unix real UID or Windows │
1139 │ │ SID │
1140 ├──────────────────┼────────────────────────────┤
1141 │%{euid} │ Unix effective user ID or │
1142 │ │ Windows SID │
1143 ├──────────────────┼────────────────────────────┤
1144 │%{USERID} │ Same as %{uid} │
1145 ├──────────────────┼────────────────────────────┤
1146 │%{null} │ Empty string │
1147 ├──────────────────┼────────────────────────────┤
1148 │%{LIBDIR} │ Installation library │
1149 │ │ directory │
1150 ├──────────────────┼────────────────────────────┤
1151 │%{BINDIR} │ Installation binary direc‐ │
1152 │ │ tory │
1153 ├──────────────────┼────────────────────────────┤
1154 │%{SBINDIR} │ Installation admin binary │
1155 │ │ directory │
1156 ├──────────────────┼────────────────────────────┤
1157 │%{username} │ (Unix) Username of effec‐ │
1158 │ │ tive user ID │
1159 ├──────────────────┼────────────────────────────┤
1160 │%{APPDATA} │ (Windows) Roaming applica‐ │
1161 │ │ tion data for current user │
1162 ├──────────────────┼────────────────────────────┤
1163 │%{COMMON_APPDATA} │ (Windows) Application data │
1164 │ │ for all users │
1165 ├──────────────────┼────────────────────────────┤
1166 │%{LOCAL_APPDATA} │ (Windows) Local applica‐ │
1167 │ │ tion data for current user │
1168 ├──────────────────┼────────────────────────────┤
1169 │%{SYSTEM} │ (Windows) Windows system │
1170 │ │ folder │
1171 ├──────────────────┼────────────────────────────┤
1172 │%{WINDOWS} │ (Windows) Windows folder │
1173 ├──────────────────┼────────────────────────────┤
1174 │%{USERCONFIG} │ (Windows) Per-user MIT │
1175 │ │ krb5 config file directory │
1176 ├──────────────────┼────────────────────────────┤
1177 │%{COMMONCONFIG} │ (Windows) Common MIT krb5 │
1178 │ │ config file directory │
1179 └──────────────────┴────────────────────────────┘
1180
1182 Here is an example of a generic krb5.conf file:
1183 [libdefaults]
1185 default_realm = ATHENA.MIT.EDU
1186 dns_lookup_kdc = true
1187 dns_lookup_realm = false
1188 [realms]
1190 ATHENA.MIT.EDU = {
1191 kdc = kerberos.mit.edu
1192 kdc = kerberos-1.mit.edu
1193 kdc = kerberos-2.mit.edu
1194 admin_server = kerberos.mit.edu
1195 master_kdc = kerberos.mit.edu
1196 }
1197 EXAMPLE.COM = {
1198 kdc = kerberos.example.com
1199 kdc = kerberos-1.example.com
1200 admin_server = kerberos.example.com
1201 }
1202 [domain_realm]
1204 mit.edu = ATHENA.MIT.EDU
1205 [capaths]
1207 ATHENA.MIT.EDU = {
1208 EXAMPLE.COM = .
1209 }
1210 EXAMPLE.COM = {
1211 ATHENA.MIT.EDU = .
1212 }
1213
1215 /etc/krb5.conf
1216
1218 syslog(3)
1219
1221 MIT
1222
1224 1985-2018, MIT
12251.16.1 KRB5.CONF(5)