Provided by: krb5-doc_1.17-6ubuntu4.8_all 
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. Multiple colon-separated filenames may be specified in KRB5_CONFIG; all files
which are present will be read. Starting in release 1.14, directory names can also be specified in
KRB5_CONFIG; all files within the directory whose names consist solely of alphanumeric characters,
dashes, or underscores will be read.
STRUCTURE
The krb5.conf file is set up in the style of a Windows INI file. Lines beginning with '#' or ';'
(possibly after initial whitespace) are ignored as comments. Sections are headed by the section name, in
square brackets. Each section 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 configuration 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. Starting in release 1.15, files with names ending in ".conf" are
also included, unless the name begins with ".". Included profile files are syntactically independent of
their parents, so each included file must begin with a section header. Starting in release 1.17, files
are read in alphanumeric order; in previous releases, they may be read in any order.
The krb5.conf file can specify that configuration should be obtained from a loadable module, rather than
the file itself, using the following 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_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 environments 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.
The clockskew setting is also used when evaluating ticket start and expiration times. For
example, tickets that have reached their expiration time can still be used (and renewed if they
are renewable tickets) if they have been expired for a shorter duration than the clockskew
setting.
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). New in
release 1.11.
default_client_keytab_name
This relation specifies the name of the default keytab for obtaining client credentials. The
default is FILE:/etc/krb5/user/%{euid}/client.keytab. This relation is subject to parameter
expansion (see below). New in release 1.11.
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_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
aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128 des3-cbc-sha1 arcfour-hmac-md5
camellia256-cts-cmac camellia128-cts-cmac, but weak 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.
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 aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128 des3-cbc-sha1
arcfour-hmac-md5 camellia256-cts-cmac camellia128-cts-cmac, but weak 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_canonicalize_hostname
Indicate whether name lookups will be used to canonicalize hostnames for use in service principal
names. Setting this flag to false can improve security by reducing reliance on DNS, but means
that short hostnames will not be canonicalized to fully-qualified hostnames. The default value is
true.
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 contact 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
verification using some secret that it won't know.
dns_uri_lookup
Indicate whether DNS URI 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. SRV records are used as a
fallback if no URI records were found. The default value is true. New in release 1.15.
err_fmt
This relation allows for custom error message formatting. If a value is set, error messages will
be formatted by substituting a normal error message for %M and an error code for %C in the value.
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 application, 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. New in
release 1.10.
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 security reasons, .k5login files
must be owned by the local user or by root.
kcm_mach_service
On macOS only, determines the name of the bootstrap service used to contact the KCM daemon for the
KCM credential cache type. If the value is -, Mach RPC will not be used to contact the KCM
daemon. The default value is org.h5l.kcm.
kcm_socket
Determines the path to the Unix domain socket used to access the KCM daemon for the KCM credential
cache type. If the value is -, Unix domain sockets will not be used to contact the KCM daemon.
The default value is /var/run/.heim_org.h5l.kcm-socket.
kdc_default_options
Default KDC options (Xored for multiple values) when requesting initial tickets. By default it is
set to 0x00000010 (KDC_OPT_RENEWABLE_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 aes256-cts-hmac-sha384-192
aes128-cts-hmac-sha256-128 des3-cbc-sha1 arcfour-hmac-md5 camellia256-cts-cmac
camellia128-cts-cmac, but weak 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. This relation is subject to parameter
expansion (see below) in release 1.17 and later.
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. If dns_canonicalize_hostname is set
to false, this flag has no effect. 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
configuration option for the possible values and their meanings.
spake_preauth_groups
A whitespace or comma-separated list of words which specifies the groups allowed for SPAKE
preauthentication. The possible values are:
┌─────────────┬───────────────────────────────┐
│edwards25519 │ Edwards25519 curve (RFC 7748) │
├─────────────┼───────────────────────────────┤
│P-256 │ NIST P-256 curve (RFC 5480) │
└─────────────┴───────────────────────────────┘
│P-384 │ NIST P-384 curve (RFC 5480) │
├─────────────┼───────────────────────────────┤
│P-521 │ NIST P-521 curve (RFC 5480) │
└─────────────┴───────────────────────────────┘
The default value for the client is edwards25519. The default value for the KDC is empty. New in
release 1.17.
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_preference_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/
auth_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 second 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).
disable_encrypted_timestamp
If this flag is true, the client will not perform encrypted timestamp preauthentication if
requested by the KDC. Setting this flag can help to prevent dictionary attacks by active
attackers, if the realm's KDCs support SPAKE preauthentication or if initial authentication always
uses another mechanism or always uses FAST. This flag persists across client referrals during
initial authentication. This flag does not prevent the KDC from offering encrypted timestamp.
New in release 1.17.
http_anchors
When KDCs and kpasswd servers are accessed through HTTPS proxies, this tag can be used to specify
the location of the CA certificate which should be trusted to issue the certificate for a proxy
server. If left unspecified, the system-wide default set of CA certificates is used.
The syntax for values is similar to that of values for the pkinit_anchors tag:
FILE: filename
filename is assumed to be the name of an OpenSSL-style ca-bundle file.
DIR: dirname
dirname is assumed to be an directory which contains CA certificates. All files in the directory
will be examined; if they contain certificates (in PEM format), they will be used.
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_CA, where environment variable
X509_PROXY_CA has been set to FILE:/tmp/my_proxy.pem.
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 distinguish 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, DNS
will be queried (unless forbidden by dns_lookup_kdc). Finally, 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 replica 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. A
host name relation implicitly provides the corresponding domain name relation, unless an explicit domain
name relation is provided. 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
.dev.mit.edu = TEST.ATHENA.MIT.EDU
mit.edu = ATHENA.MIT.EDU
maps the host with the name crash.mit.edu into the TEST.ATHENA.MIT.EDU realm. The second entry maps all
hosts under the domain dev.mit.edu into the TEST.ATHENA.MIT.EDU realm, but not the host with the name
dev.mit.edu. That host is matched by the third entry, which maps the host mit.edu and all hosts under
the domain mit.edu that do not match a preceding rule into the realm ATHENA.MIT.EDU.
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 hostname'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 intermediate 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 subtags 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]
• pwqual interface
• kadm5_hook interface
• 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.
New in release 1.9.
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].
For pluggable interfaces where module order matters, modules registered with a module tag normally come
first, in the order they are registered, followed by built-in modules in the order they are documented
below. If enable_only tags are used, then the order of those tags overrides the normal module order.
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
hostname
If the service principal is host-based, uses the service hostname 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 interface 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.
kadm5_auth interface
The kadm5_auth section (introduced in release 1.16) controls modules for the kadmin authorization
interface, which determines whether a client principal is allowed to perform a kadmin operation. The
following built-in modules exist for this interface:
acl This module reads the kadm5.acl(5) file, and authorizes operations which are allowed according to
the rules in the file.
self This module authorizes self-service operations including password changes, creation of new random
keys, fetching the client's principal record or string attributes, and fetching the policy record
associated with the client principal.
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.
hostrealm interface
The hostrealm section (introduced in release 1.12) controls modules for the host-to-realm interface,
which affects the local mapping of hostnames to realm names and the choice of default realm. The
following built-in modules exist for this interface:
profile
This module consults the [domain_realm] section of the profile for authoritative host-to-realm
mappings, and the default_realm variable for the default realm.
dns This module looks for DNS records for fallback host-to-realm mappings and the default realm. It
only operates if the dns_lookup_realm variable is set to true.
domain This module applies heuristics for fallback host-to-realm mappings. It implements the
realm_try_domains variable, and uses the uppercased parent domain of the hostname if that does not
produce a result.
localauth interface
The localauth section (introduced in release 1.12) controls modules for the local authorization
interface, which affects the relationship between Kerberos principals and local system accounts. The
following built-in modules exist for this interface:
default
This module implements the DEFAULT type for auth_to_local values.
rule This module implements the RULE type for auth_to_local values.
names This module looks for an auth_to_local_names mapping for the principal name.
auth_to_local
This module processes auth_to_local values in the default realm's section, and applies the default
method if no auth_to_local values exist.
k5login
This module authorizes a principal to a local account according to the account's .k5login(5) file.
an2ln This module authorizes a principal to a local account if the principal name maps to the local
account name.
certauth interface
The certauth section (introduced in release 1.16) controls modules for the certificate authorization
interface, which determines whether a certificate is allowed to preauthenticate a user via PKINIT. The
following built-in modules exist for this interface:
pkinit_san
This module authorizes the certificate if it contains a PKINIT Subject Alternative Name for the
requested client principal, or a Microsoft UPN SAN matching the principal if pkinit_allow_upn is
set to true for the realm.
pkinit_eku
This module rejects the certificate if it does not contain an Extended Key Usage attribute
consistent with the pkinit_eku_checking value for the realm.
dbmatch
This module authorizes or rejects the certificate according to whether it matches the
pkinit_cert_match string attribute on the client principal, if that attribute is present.
PKINIT OPTIONS
NOTE:
The following are PKINIT-specific options. These values may be specified in [libdefaults] as global
defaults, or within a realm-specific subsection of [libdefaults], or may be specified as
realm-specific values in the [realms] section. A realm-specific value overrides, 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 contain 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 revocation 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 configuration 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 attempting 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 values.
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:
• pkinit
• msScLogin
• clientAuth
• emailProtection
key-usage-list is a comma-separated list of required Key Usage values. All values in the
list must be present in the certificate. Key Usage values can be:
• digitalSignature
• 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 will be
accepted. This key usage value is used in most commercially issued server certificates.
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. If this
option is specified multiple times, the first valid value is used; this can be used to specify an
environment variable (with ENV:envvar) followed by a default value. 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_pool
Specifies the location of intermediate certificates which may be used by the client to complete
the trust chain between a KDC certificate 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.
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
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
admin_server = kerberos.mit.edu
master_kdc = kerberos.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
[capaths]
ATHENA.MIT.EDU = {
EXAMPLE.COM = .
}
EXAMPLE.COM = {
ATHENA.MIT.EDU = .
}
FILES
/etc/krb5.conf
SEE ALSO
syslog(3)
AUTHOR
MIT
COPYRIGHT
1985-2019, MIT