KRB5.CONF(5) MIT Kerberos KRB5.CONF(5)
NAME
krb5.conf - Kerberos configuration file
The krb5.conf file contains Kerberos configuration information, including the locations of KDCs and admin servers for the Kerberos realms
of interest, defaults for the current realm and for Kerberos applications, and mappings of hostnames onto Kerberos realms. Normally, you
should install your krb5.conf file in the directory /etc. You can override the default location by setting the environment variable
KRB5_CONFIG.
STRUCTURE
The krb5.conf file is set up in the style of a Windows INI file. Sections are headed by the section name, in square brackets. Each sec-
tion may contain zero or more relations, of the form:
foo = bar
or
fubar = {
foo = bar
baz = quux
}
Placing a '*' at the end of a line indicates that this is the final value for the tag. This means that neither the remainder of this con-
figuration file nor any other configuration file will be checked for any other values for this tag.
For example, if you have the following lines:
foo = bar*
foo = baz
then the second value of foo (baz) would never be read.
The krb5.conf file can include other files using either of the following directives at the beginning of a line:
include FILENAME
includedir DIRNAME
FILENAME or DIRNAME should be an absolute path. The named file or directory must exist and be readable. Including a directory includes all
files within the directory whose names consist solely of alphanumeric characters, dashes, or underscores. Included profile files are syn-
tactically independent of their parents, so each included file must begin with a section header.
The krb5.conf file can specify that configuration should be obtained from a loadable module, rather than the file itself, using the follow-
ing directive at the beginning of a line before any section headers:
module MODULEPATH:RESIDUAL
MODULEPATH may be relative to the library path of the krb5 installation, or it may be an absolute path. RESIDUAL is provided to the module
at initialization time. If krb5.conf uses a module directive, kdc.conf(5) should also use one if it exists.
SECTIONS
The krb5.conf file may contain the following sections:
+---------------+---------------------------------------------------+
|[libdefaults] | Settings used by the Kerberos V5 library |
+---------------+---------------------------------------------------+
|[realms] | Realm-specific contact information and settings |
+---------------+---------------------------------------------------+
|[domain_realm] | Maps server hostnames to Kerberos realms |
+---------------+---------------------------------------------------+
|[capaths] | Authentication paths for non-hierarchical |
| | cross-realm |
+---------------+---------------------------------------------------+
|[appdefaults] | Settings used by some Kerberos V5 applications |
+---------------+---------------------------------------------------+
|[plugins] | Controls plugin module registration |
+---------------+---------------------------------------------------+
Additionally, krb5.conf may include any of the relations described in kdc.conf(5), but it is not a recommended practice.
[libdefaults]
The libdefaults section may contain any of the following relations:
allow_weak_crypto
If this flag is set to false, then weak encryption types (as noted in Encryption_and_salt_types in kdc.conf(5)) will be filtered out
of the lists default_tgs_enctypes, default_tkt_enctypes, and permitted_enctypes. The default value for this tag is false, which may
cause authentication failures in existing Kerberos infrastructures that do not support strong crypto. Users in affected environ-
ments should set this tag to true until their infrastructure adopts stronger ciphers.
ap_req_checksum_type
An integer which specifies the type of AP-REQ checksum to use in authenticators. This variable should be unset so the appropriate
checksum for the encryption key in use will be used. This can be set if backward compatibility requires a specific checksum type.
See the kdc_req_checksum_type configuration option for the possible values and their meanings.
canonicalize
If this flag is set to true, initial ticket requests to the KDC will request canonicalization of the client principal name, and
answers with different client principals than the requested principal will be accepted. The default value is false.
ccache_type
This parameter determines the format of credential cache types created by kinit(1) or other programs. The default value is 4, which
represents the most current format. Smaller values can be used for compatibility with very old implementations of Kerberos which
interact with credential caches on the same host.
clockskew
Sets the maximum allowable amount of clockskew in seconds that the library will tolerate before assuming that a Kerberos message is
invalid. The default value is 300 seconds, or five minutes.
default_ccache_name
This relation specifies the name of the default credential cache. The default is FILE:/tmp/krb5cc_%{uid}. This relation is subject
to parameter expansion (see below).
default_client_keytab_name
This relation specifies the name of the default keytab for obtaining client credentials. The default is FILE:/var/ker-
beros/krb5/user/%{euid}/client.keytab. This relation is subject to parameter expansion (see below).
default_keytab_name
This relation specifies the default keytab name to be used by application servers such as sshd. The default is
FILE:/etc/krb5.keytab. This relation is subject to parameter expansion (see below).
default_realm
Identifies the default Kerberos realm for the client. Set its value to your Kerberos realm. If this value is not set, then a realm
must be specified with every Kerberos principal when invoking programs such as kinit(1).
default_tgs_enctypes
Identifies the supported list of session key encryption types that the client should request when making a TGS-REQ, in order of
preference from highest to lowest. The list may be delimited with commas or whitespace. See Encryption_and_salt_types in
kdc.conf(5) for a list of the accepted values for this tag. The default value is aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
des3-cbc-sha1 arcfour-hmac-md5 camellia256-cts-cmac camellia128-cts-cmac des-cbc-crc des-cbc-md5 des-cbc-md4, but single-DES encryp-
tion types will be implicitly removed from this list if the value of allow_weak_crypto is false.
Do not set this unless required for specific backward compatibility purposes; stale values of this setting can prevent clients from
taking advantage of new stronger enctypes when the libraries are upgraded.
default_tkt_enctypes
Identifies the supported list of session key encryption types that the client should request when making an AS-REQ, in order of
preference from highest to lowest. The format is the same as for default_tgs_enctypes. The default value for this tag is
aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96 des3-cbc-sha1 arcfour-hmac-md5 camellia256-cts-cmac camellia128-cts-cmac des-cbc-crc
des-cbc-md5 des-cbc-md4, but single-DES encryption types will be implicitly removed from this list if the value of allow_weak_crypto
is false.
Do not set this unless required for specific backward compatibility purposes; stale values of this setting can prevent clients from
taking advantage of new stronger enctypes when the libraries are upgraded.
dns_lookup_kdc
Indicate whether DNS SRV records should be used to locate the KDCs and other servers for a realm, if they are not listed in the
krb5.conf information for the realm. (Note that the admin_server entry must be in the krb5.conf realm information in order to con-
tact kadmind, because the DNS implementation for kadmin is incomplete.)
Enabling this option does open up a type of denial-of-service attack, if someone spoofs the DNS records and redirects you to another
server. However, it's no worse than a denial of service, because that fake KDC will be unable to decode anything you send it
(besides the initial ticket request, which has no encrypted data), and anything the fake KDC sends will not be trusted without veri-
fication using some secret that it won't know.
extra_addresses
This allows a computer to use multiple local addresses, in order to allow Kerberos to work in a network that uses NATs while still
using address-restricted tickets. The addresses should be in a comma-separated list. This option has no effect if noaddresses is
true.
forwardable
If this flag is true, initial tickets will be forwardable by default, if allowed by the KDC. The default value is false.
ignore_acceptor_hostname
When accepting GSSAPI or krb5 security contexts for host-based service principals, ignore any hostname passed by the calling appli-
cation, and allow clients to authenticate to any service principal in the keytab matching the service name and realm name (if
given). This option can improve the administrative flexibility of server applications on multihomed hosts, but could compromise the
security of virtual hosting environments. The default value is false.
k5login_authoritative
If this flag is true, principals must be listed in a local user's k5login file to be granted login access, if a .k5login(5) file
exists. If this flag is false, a principal may still be granted login access through other mechanisms even if a k5login file exists
but does not list the principal. The default value is true.
k5login_directory
If set, the library will look for a local user's k5login file within the named directory, with a filename corresponding to the local
username. If not set, the library will look for k5login files in the user's home directory, with the filename .k5login. For secu-
rity reasons, .k5login files must be owned by the local user or by root.
kdc_default_options
Default KDC options (Xored for multiple values) when requesting initial tickets. By default it is set to 0x00000010 (KDC_OPT_RENEW-
ABLE_OK).
kdc_timesync
Accepted values for this relation are 1 or 0. If it is nonzero, client machines will compute the difference between their time and
the time returned by the KDC in the timestamps in the tickets and use this value to correct for an inaccurate system clock when
requesting service tickets or authenticating to services. This corrective factor is only used by the Kerberos library; it is not
used to change the system clock. The default value is 1.
kdc_req_checksum_type
An integer which specifies the type of checksum to use for the KDC requests, for compatibility with very old KDC implementations.
This value is only used for DES keys; other keys use the preferred checksum type for those keys.
The possible values and their meanings are as follows.
+-----+----------------------------------+
|1 | CRC32 |
+-----+----------------------------------+
|2 | RSA MD4 |
+-----+----------------------------------+
|3 | RSA MD4 DES |
+-----+----------------------------------+
|4 | DES CBC |
+-----+----------------------------------+
|7 | RSA MD5 |
+-----+----------------------------------+
|8 | RSA MD5 DES |
+-----+----------------------------------+
|9 | NIST SHA |
+-----+----------------------------------+
|12 | HMAC SHA1 DES3 |
+-----+----------------------------------+
|-138 | Microsoft MD5 HMAC checksum type |
+-----+----------------------------------+
noaddresses
If this flag is true, requests for initial tickets will not be made with address restrictions set, allowing the tickets to be used
across NATs. The default value is true.
permitted_enctypes
Identifies all encryption types that are permitted for use in session key encryption. The default value for this tag is
aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96 des3-cbc-sha1 arcfour-hmac-md5 camellia256-cts-cmac camellia128-cts-cmac des-cbc-crc
des-cbc-md5 des-cbc-md4, but single-DES encryption types will be implicitly removed from this list if the value of allow_weak_crypto
is false.
plugin_base_dir
If set, determines the base directory where krb5 plugins are located. The default value is the krb5/plugins subdirectory of the
krb5 library directory.
preferred_preauth_types
This allows you to set the preferred preauthentication types which the client will attempt before others which may be advertised by
a KDC. The default value for this setting is "17, 16, 15, 14", which forces libkrb5 to attempt to use PKINIT if it is supported.
proxiable
If this flag is true, initial tickets will be proxiable by default, if allowed by the KDC. The default value is false.
rdns If this flag is true, reverse name lookup will be used in addition to forward name lookup to canonicalizing hostnames for use in
service principal names. The default value is true.
realm_try_domains
Indicate whether a host's domain components should be used to determine the Kerberos realm of the host. The value of this variable
is an integer: -1 means not to search, 0 means to try the host's domain itself, 1 means to also try the domain's immediate parent,
and so forth. The library's usual mechanism for locating Kerberos realms is used to determine whether a domain is a valid realm,
which may involve consulting DNS if dns_lookup_kdc is set. The default is not to search domain components.
renew_lifetime
(duration string.) Sets the default renewable lifetime for initial ticket requests. The default value is 0.
safe_checksum_type
An integer which specifies the type of checksum to use for the KRB-SAFE requests. By default it is set to 8 (RSA MD5 DES). For
compatibility with applications linked against DCE version 1.1 or earlier Kerberos libraries, use a value of 3 to use the RSA MD4
DES instead. This field is ignored when its value is incompatible with the session key type. See the kdc_req_checksum_type config-
uration option for the possible values and their meanings.
ticket_lifetime
(duration string.) Sets the default lifetime for initial ticket requests. The default value is 1 day.
udp_preference_limit
When sending a message to the KDC, the library will try using TCP before UDP if the size of the message is above udp_prefer-
ence_limit. If the message is smaller than udp_preference_limit, then UDP will be tried before TCP. Regardless of the size, both
protocols will be tried if the first attempt fails.
verify_ap_req_nofail
If this flag is true, then an attempt to verify initial credentials will fail if the client machine does not have a keytab. The
default value is false.
[realms]
Each tag in the [realms] section of the file is the name of a Kerberos realm. The value of the tag is a subsection with relations that
define the properties of that particular realm. For each realm, the following tags may be specified in the realm's subsection:
admin_server
Identifies the host where the administration server is running. Typically, this is the master Kerberos server. This tag must be
given a value in order to communicate with the kadmind(8) server for the realm.
auth_to_local
This tag allows you to set a general rule for mapping principal names to local user names. It will be used if there is not an
explicit mapping for the principal name that is being translated. The possible values are:
RULE:exp
The local name will be formulated from exp.
The format for exp is [n:string](regexp)s/pattern/replacement/g. The integer n indicates how many components the target
principal should have. If this matches, then a string will be formed from string, substituting the realm of the principal
for $0 and the n'th component of the principal for $n (e.g., if the principal was johndoe/admin then [2:$2$1foo] would result
in the string adminjohndoefoo). If this string matches regexp, then the s//[g] substitution command will be run over the
string. The optional g will cause the substitution to be global over the string, instead of replacing only the first match
in the string.
DEFAULT
The principal name will be used as the local user name. If the principal has more than one component or is not in the
default realm, this rule is not applicable and the conversion will fail.
For example:
[realms]
ATHENA.MIT.EDU = {
auth_to_local = RULE:[2:$1](johndoe)s/^.*$/guest/
auth_to_local = RULE:[2:$1;$2](^.*;admin$)s/;admin$//
auth_to_local = RULE:[2:$2](^.*;root)s/^.*$/root/
auto_to_local = DEFAULT
}
would result in any principal without root or admin as the second component to be translated with the default rule. A principal
with a second component of admin will become its first component. root will be used as the local name for any principal with a sec-
ond component of root. The exception to these two rules are any principals johndoe/*, which will always get the local name guest.
auth_to_local_names
This subsection allows you to set explicit mappings from principal names to local user names. The tag is the mapping name, and the
value is the corresponding local user name.
default_domain
This tag specifies the domain used to expand hostnames when translating Kerberos 4 service principals to Kerberos 5 principals (for
example, when converting rcmd.hostname to host/hostname.domain).
kdc The name or address of a host running a KDC for that realm. An optional port number, separated from the hostname by a colon, may be
included. If the name or address contains colons (for example, if it is an IPv6 address), enclose it in square brackets to distin-
guish the colon from a port separator. For your computer to be able to communicate with the KDC for each realm, this tag must be
given a value in each realm subsection in the configuration file, or there must be DNS SRV records specifying the KDCs.
kpasswd_server
Points to the server where all the password changes are performed. If there is no such entry, the port 464 on the admin_server host
will be tried.
master_kdc
Identifies the master KDC(s). Currently, this tag is used in only one case: If an attempt to get credentials fails because of an
invalid password, the client software will attempt to contact the master KDC, in case the user's password has just been changed, and
the updated database has not been propagated to the slave servers yet.
v4_instance_convert
This subsection allows the administrator to configure exceptions to the default_domain mapping rule. It contains V4 instances (the
tag name) which should be translated to some specific hostname (the tag value) as the second component in a Kerberos V5 principal
name.
v4_realm
This relation is used by the krb524 library routines when converting a V5 principal name to a V4 principal name. It is used when
the V4 realm name and the V5 realm name are not the same, but still share the same principal names and passwords. The tag value is
the Kerberos V4 realm name.
[domain_realm]
The [domain_realm] section provides a translation from a domain name or hostname to a Kerberos realm name. The tag name can be a host name
or domain name, where domain names are indicated by a prefix of a period (.). The value of the relation is the Kerberos realm name for
that particular host or domain. The Kerberos realm may be identified either in the realms section or using DNS SRV records. Host names
and domain names should be in lower case. For example:
[domain_realm]
crash.mit.edu = TEST.ATHENA.MIT.EDU
.mit.edu = ATHENA.MIT.EDU
mit.edu = ATHENA.MIT.EDU
maps the host with the exact name crash.mit.edu into the TEST.ATHENA.MIT.EDU realm. The period prefix in .mit.edu denotes that all systems
in the mit.edu domain belong to ATHENA.MIT.EDU realm. The third entry maps the host mit.edu itself to the ATHENA.MIT.EDU realm.
If no translation entry applies to a hostname used for a service principal for a service ticket request, the library will try to get a
referral to the appropriate realm from the client realm's KDC. If that does not succeed, the host's realm is considered to be the host-
name's domain portion converted to uppercase, unless the realm_try_domains setting in [libdefaults] causes a different parent domain to be
used.
[capaths]
In order to perform direct (non-hierarchical) cross-realm authentication, configuration is needed to determine the authentication paths
between realms.
A client will use this section to find the authentication path between its realm and the realm of the server. The server will use this
section to verify the authentication path used by the client, by checking the transited field of the received ticket.
There is a tag for each participating client realm, and each tag has subtags for each of the server realms. The value of the subtags is an
intermediate realm which may participate in the cross-realm authentication. The subtags may be repeated if there is more then one interme-
diate realm. A value of "." means that the two realms share keys directly, and no intermediate realms should be allowed to participate.
Only those entries which will be needed on the client or the server need to be present. A client needs a tag for its local realm with sub-
tags for all the realms of servers it will need to authenticate to. A server needs a tag for each realm of the clients it will serve, with
a subtag of the server realm.
For example, ANL.GOV, PNL.GOV, and NERSC.GOV all wish to use the ES.NET realm as an intermediate realm. ANL has a sub realm of
TEST.ANL.GOV which will authenticate with NERSC.GOV but not PNL.GOV. The [capaths] section for ANL.GOV systems would look like this:
[capaths]
ANL.GOV = {
TEST.ANL.GOV = .
PNL.GOV = ES.NET
NERSC.GOV = ES.NET
ES.NET = .
}
TEST.ANL.GOV = {
ANL.GOV = .
}
PNL.GOV = {
ANL.GOV = ES.NET
}
NERSC.GOV = {
ANL.GOV = ES.NET
}
ES.NET = {
ANL.GOV = .
}
The [capaths] section of the configuration file used on NERSC.GOV systems would look like this:
[capaths]
NERSC.GOV = {
ANL.GOV = ES.NET
TEST.ANL.GOV = ES.NET
TEST.ANL.GOV = ANL.GOV
PNL.GOV = ES.NET
ES.NET = .
}
ANL.GOV = {
NERSC.GOV = ES.NET
}
PNL.GOV = {
NERSC.GOV = ES.NET
}
ES.NET = {
NERSC.GOV = .
}
TEST.ANL.GOV = {
NERSC.GOV = ANL.GOV
NERSC.GOV = ES.NET
}
When a subtag is used more than once within a tag, clients will use the order of values to determine the path. The order of values is not
important to servers.
[appdefaults]
Each tag in the [appdefaults] section names a Kerberos V5 application or an option that is used by some Kerberos V5 application[s]. The
value of the tag defines the default behaviors for that application.
For example:
[appdefaults]
telnet = {
ATHENA.MIT.EDU = {
option1 = false
}
}
telnet = {
option1 = true
option2 = true
}
ATHENA.MIT.EDU = {
option2 = false
}
option2 = true
The above four ways of specifying the value of an option are shown in order of decreasing precedence. In this example, if telnet is running
in the realm EXAMPLE.COM, it should, by default, have option1 and option2 set to true. However, a telnet program in the realm
ATHENA.MIT.EDU should have option1 set to false and option2 set to true. Any other programs in ATHENA.MIT.EDU should have option2 set to
false by default. Any programs running in other realms should have option2 set to true.
The list of specifiable options for each application may be found in that application's man pages. The application defaults specified here
are overridden by those specified in the realms section.
[plugins]
o pwqual interface
o kadm5_hook interface
o clpreauth and kdcpreauth interfaces
Tags in the [plugins] section can be used to register dynamic plugin modules and to turn modules on and off. Not every krb5 pluggable
interface uses the [plugins] section; the ones that do are documented here.
Each pluggable interface corresponds to a subsection of [plugins]. All subsections support the same tags:
disable
This tag may have multiple values. If there are values for this tag, then the named modules will be disabled for the pluggable
interface.
enable_only
This tag may have multiple values. If there are values for this tag, then only the named modules will be enabled for the pluggable
interface.
module This tag may have multiple values. Each value is a string of the form modulename:pathname, which causes the shared object located
at pathname to be registered as a dynamic module named modulename for the pluggable interface. If pathname is not an absolute path,
it will be treated as relative to the plugin_base_dir value from [libdefaults].
The following subsections are currently supported within the [plugins] section:
ccselect interface
The ccselect subsection controls modules for credential cache selection within a cache collection. In addition to any registered dynamic
modules, the following built-in modules exist (and may be disabled with the disable tag):
k5identity
Uses a .k5identity file in the user's home directory to select a client principal
realm Uses the service realm to guess an appropriate cache from the collection
pwqual interface
The pwqual subsection controls modules for the password quality interface, which is used to reject weak passwords when passwords are
changed. The following built-in modules exist for this interface:
dict Checks against the realm dictionary file
empty Rejects empty passwords
hesiod Checks against user information stored in Hesiod (only if Kerberos was built with Hesiod support)
princ Checks against components of the principal name
kadm5_hook interface
The kadm5_hook interface provides plugins with information on principal creation, modification, password changes and deletion. This inter-
face can be used to write a plugin to synchronize MIT Kerberos with another database such as Active Directory. No plugins are built in for
this interface.
clpreauth and kdcpreauth interfaces
The clpreauth and kdcpreauth interfaces allow plugin modules to provide client and KDC preauthentication mechanisms. The following
built-in modules exist for these interfaces:
pkinit This module implements the PKINIT preauthentication mechanism.
encrypted_challenge
This module implements the encrypted challenge FAST factor.
encrypted_timestamp
This module implements the encrypted timestamp mechanism.
PKINIT OPTIONS
NOTE:
The following are PKINIT-specific options. These values may be specified in [libdefaults] as global defaults, or within a realm-spe-
cific subsection of [libdefaults], or may be specified as realm-specific values in the [realms] section. A realm-specific value over-
rides, not adds to, a generic [libdefaults] specification. The search order is:
1. realm-specific subsection of [libdefaults]:
[libdefaults]
EXAMPLE.COM = {
pkinit_anchors = FILE:/usr/local/example.com.crt
}
2. realm-specific value in the [realms] section,
[realms]
OTHERREALM.ORG = {
pkinit_anchors = FILE:/usr/local/otherrealm.org.crt
}
3. generic value in the [libdefaults] section.
[libdefaults]
pkinit_anchors = DIR:/usr/local/generic_trusted_cas/
Specifying PKINIT identity information
The syntax for specifying Public Key identity, trust, and revocation information for PKINIT is as follows:
FILE:filename[,keyfilename]
This option has context-specific behavior.
In pkinit_identity or pkinit_identities, filename specifies the name of a PEM-format file containing the user's certificate. If
keyfilename is not specified, the user's private key is expected to be in filename as well. Otherwise, keyfilename is the name of
the file containing the private key.
In pkinit_anchors or pkinit_pool, filename is assumed to be the name of an OpenSSL-style ca-bundle file.
DIR:dirname
This option has context-specific behavior.
In pkinit_identity or pkinit_identities, dirname specifies a directory with files named *.crt and *.key where the first part of the
file name is the same for matching pairs of certificate and private key files. When a file with a name ending with .crt is found, a
matching file ending with .key is assumed to contain the private key. If no such file is found, then the certificate in the .crt is
not used.
In pkinit_anchors or pkinit_pool, dirname is assumed to be an OpenSSL-style hashed CA directory where each CA cert is stored in a
file named hash-of-ca-cert.#. This infrastructure is encouraged, but all files in the directory will be examined and if they con-
tain certificates (in PEM format), they will be used.
In pkinit_revoke, dirname is assumed to be an OpenSSL-style hashed CA directory where each revocation list is stored in a file named
hash-of-ca-cert.r#. This infrastructure is encouraged, but all files in the directory will be examined and if they contain a revo-
cation list (in PEM format), they will be used.
PKCS12:filename
filename is the name of a PKCS #12 format file, containing the user's certificate and private key.
PKCS11:[module_name=]modname[:slotid=slot-id][:token=token-label][:certid=cert-id][:certlabel=cert-label]
All keyword/values are optional. modname specifies the location of a library implementing PKCS #11. If a value is encountered with
no keyword, it is assumed to be the modname. If no module-name is specified, the default is opensc-pkcs11.so. slotid= and/or
token= may be specified to force the use of a particular smard card reader or token if there is more than one available. certid=
and/or certlabel= may be specified to force the selection of a particular certificate on the device. See the pkinit_cert_match con-
figuration option for more ways to select a particular certificate to use for PKINIT.
ENV:envvar
envvar specifies the name of an environment variable which has been set to a value conforming to one of the previous values. For
example, ENV:X509_PROXY, where environment variable X509_PROXY has been set to FILE:/tmp/my_proxy.pem.
PKINIT krb5.conf options
pkinit_anchors
Specifies the location of trusted anchor (root) certificates which the client trusts to sign KDC certificates. This option may be
specified multiple times. These values from the config file are not used if the user specifies X509_anchors on the command line.
pkinit_cert_match
Specifies matching rules that the client certificate must match before it is used to attempt PKINIT authentication. If a user has
multiple certificates available (on a smart card, or via other media), there must be exactly one certificate chosen before attempt-
ing PKINIT authentication. This option may be specified multiple times. All the available certificates are checked against each
rule in order until there is a match of exactly one certificate.
The Subject and Issuer comparison strings are the RFC 2253 string representations from the certificate Subject DN and Issuer DN val-
ues.
The syntax of the matching rules is:
[relation-operator]component-rule ...
where:
relation-operator
can be either &&, meaning all component rules must match, or ||, meaning only one component rule must match. The default is
&&.
component-rule
can be one of the following. Note that there is no punctuation or whitespace between component rules.
<SUBJECT>regular-expression
<ISSUER>regular-expression
<SAN>regular-expression
<EKU>extended-key-usage-list
<KU>key-usage-list
extended-key-usage-list is a comma-separated list of required Extended Key Usage values. All values in the list must be
present in the certificate. Extended Key Usage values can be:
o pkinit
o msScLogin
o clientAuth
o emailProtection
key-usage-list is a comma-separated list of required Key Usage values. All values in the list must be present in the cer-
tificate. Key Usage values can be:
o digitalSignature
o keyEncipherment
Examples:
pkinit_cert_match = ||<SUBJECT>.*DoE.*<SAN>.*@EXAMPLE.COM
pkinit_cert_match = &&<EKU>msScLogin,clientAuth<ISSUER>.*DoE.*
pkinit_cert_match = <EKU>msScLogin,clientAuth<KU>digitalSignature
pkinit_eku_checking
This option specifies what Extended Key Usage value the KDC certificate presented to the client must contain. (Note that if the KDC
certificate has the pkinit SubjectAlternativeName encoded as the Kerberos TGS name, EKU checking is not necessary since the issuing
CA has certified this as a KDC certificate.) The values recognized in the krb5.conf file are:
kpKDC This is the default value and specifies that the KDC must have the id-pkinit-KPKdc EKU as defined in RFC 4556.
kpServerAuth
If kpServerAuth is specified, a KDC certificate with the id-kp-serverAuth EKU as used by Microsoft will be accepted.
none If none is specified, then the KDC certificate will not be checked to verify it has an acceptable EKU. The use of this
option is not recommended.
pkinit_dh_min_bits
Specifies the size of the Diffie-Hellman key the client will attempt to use. The acceptable values are 1024, 2048, and 4096. The
default is 2048.
pkinit_identities
Specifies the location(s) to be used to find the user's X.509 identity information. This option may be specified multiple times.
Each value is attempted in order until identity information is found and authentication is attempted. Note that these values are
not used if the user specifies X509_user_identity on the command line.
pkinit_kdc_hostname
The presense of this option indicates that the client is willing to accept a KDC certificate with a dNSName SAN (Subject Alternative
Name) rather than requiring the id-pkinit-san as defined in RFC 4556. This option may be specified multiple times. Its value
should contain the acceptable hostname for the KDC (as contained in its certificate).
pkinit_longhorn
If this flag is set to true, we are talking to the Longhorn KDC.
pkinit_pool
Specifies the location of intermediate certificates which may be used by the client to complete the trust chain between a KDC cer-
tificate and a trusted anchor. This option may be specified multiple times.
pkinit_require_crl_checking
The default certificate verification process will always check the available revocation information to see if a certificate has been
revoked. If a match is found for the certificate in a CRL, verification fails. If the certificate being verified is not listed in
a CRL, or there is no CRL present for its issuing CA, and pkinit_require_crl_checking is false, then verification succeeds.
However, if pkinit_require_crl_checking is true and there is no CRL information available for the issuing CA, then verification
fails.
pkinit_require_crl_checking should be set to true if the policy is such that up-to-date CRLs must be present for every CA.
pkinit_revoke
Specifies the location of Certificate Revocation List (CRL) information to be used by the client when verifying the validity of the
KDC certificate presented. This option may be specified multiple times.
pkinit_win2k
This flag specifies whether the target realm is assumed to support only the old, pre-RFC version of the protocol. The default is
false.
pkinit_win2k_require_binding
If this flag is set to true, it expects that the target KDC is patched to return a reply with a checksum rather than a nonce. The
default is false.
PARAMETER EXPANSION
Starting with release 1.11, several variables, such as default_keytab_name, allow parameters to be expanded. Valid parameters are:
+------------------+---------------------------------------------------+
|%{TEMP} | Temporary directory |
+------------------+---------------------------------------------------+
|%{uid} | Unix real UID or Windows SID |
+------------------+---------------------------------------------------+
|%{euid} | Unix effective user ID or Windows SID |
+------------------+---------------------------------------------------+
|%{USERID} | Same as %{uid} |
+------------------+---------------------------------------------------+
|%{null} | Empty string |
+------------------+---------------------------------------------------+
|%{LIBDIR} | Installation library directory |
+------------------+---------------------------------------------------+
|%{BINDIR} | Installation binary directory |
+------------------+---------------------------------------------------+
|%{SBINDIR} | Installation admin binary directory |
+------------------+---------------------------------------------------+
|%{username} | (Unix) Username of effective user ID |
+------------------+---------------------------------------------------+
|%{APPDATA} | (Windows) Roaming application data for current |
| | user |
+------------------+---------------------------------------------------+
|%{COMMON_APPDATA} | (Windows) Application data for all users |
+------------------+---------------------------------------------------+
|%{LOCAL_APPDATA} | (Windows) Local application data for current user |
+------------------+---------------------------------------------------+
|%{SYSTEM} | (Windows) Windows system folder |
+------------------+---------------------------------------------------+
|%{WINDOWS} | (Windows) Windows folder |
+------------------+---------------------------------------------------+
|%{USERCONFIG} | (Windows) Per-user MIT krb5 config file directory |
+------------------+---------------------------------------------------+
|%{COMMONCONFIG} | (Windows) Common MIT krb5 config file directory |
+------------------+---------------------------------------------------+
SAMPLE KRB5.CONF FILE
Here is an example of a generic krb5.conf file:
[libdefaults]
default_realm = ATHENA.MIT.EDU
default_tkt_enctypes = des3-hmac-sha1 des-cbc-crc
default_tgs_enctypes = des3-hmac-sha1 des-cbc-crc
dns_lookup_kdc = true
dns_lookup_realm = false
[realms]
ATHENA.MIT.EDU = {
kdc = kerberos.mit.edu
kdc = kerberos-1.mit.edu
kdc = kerberos-2.mit.edu:750
admin_server = kerberos.mit.edu
master_kdc = kerberos.mit.edu
default_domain = mit.edu
}
EXAMPLE.COM = {
kdc = kerberos.example.com
kdc = kerberos-1.example.com
admin_server = kerberos.example.com
}
[domain_realm]
.mit.edu = ATHENA.MIT.EDU
mit.edu = ATHENA.MIT.EDU
[capaths]
ATHENA.MIT.EDU = {
EXAMPLE.COM = .
}
EXAMPLE.COM = {
ATHENA.MIT.EDU = .
}
FILES
/etc/krb5.conf
SEE ALSO
syslog(3)
AUTHOR
MIT
COPYRIGHT
1985-2013, MIT
1.11.3 KRB5.CONF(5)