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:/var/kerberos/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 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.

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_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 OS X 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 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. 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.

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.

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:

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 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).

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 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.

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].

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

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

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.

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.

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.

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.

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_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:

where:

<SUBJECT>regular-expression
<ISSUER>regular-expression
<SAN>regular-expression
<EKU>extended-key-usage-list
<KU>key-usage-list

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:

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_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.