Wallet::Object::Keytab

(Keytab object implementation for wallet)

SYNOPSIS

    my @name = qw(keytab host/shell.example.com);
    my @trace = ($user, $host, time);
    my $object = Wallet::Object::Keytab->create (@name, $schema, @trace);
    my $keytab = $object->get (@trace);
    $object->destroy (@trace);

DESCRIPTION

Wallet::Object::Keytab is a representation of Kerberos keytab objects in the wallet. It implements the wallet object API and provides the necessary glue to create principals in a Kerberos KDC, create and return keytabs for those principals, and delete them out of Kerberos when the wallet object is destroyed.

A keytab is an on-disk store for the key or keys for a Kerberos principal. Keytabs are used by services to verify incoming authentication from clients or by automated processes that need to authenticate to Kerberos. To create a keytab, the principal has to be created in Kerberos and then a keytab is generated and stored in a file on disk.

This implementation generates a new random key (and hence invalidates all existing keytabs) each time the keytab is retrieved with the get() method.

To use this object, several configuration parameters must be set. See Wallet::Config for details on those configuration parameters and information about how to set wallet configuration.

METHODS

This object mostly inherits from Wallet::Object::Base. See the documentation for that class for all generic methods. Below are only those methods that are overridden or behave specially for this implementation.

attr(ATTRIBUTE [, VALUES, PRINCIPAL, HOSTNAME [, DATETIME]])

Sets or retrieves a given object attribute. The following attribute is supported:

enctypes

Restricts the generated keytab to a specific set of encryption types. The values of this attribute must be enctype strings recognized by Kerberos (strings like aes256-cts-hmac-sha1-96 or des-cbc-crc). Encryption types must also be present in the list of supported enctypes stored in the database database or the attr() method will reject them. Note that the salt should not be included; since the salt is irrelevant for keytab keys, it will always be set to the default by the wallet.

If this attribute is set, the principal will be restricted to that specific enctype list when get() is called for that keytab. If it is not set, the default set in the KDC will be used.

This attribute is ignored if the unchanging flag is set on a keytab. Keytabs retrieved with unchanging set will contain all keys present in the KDC for that Kerberos principal and therefore may contain different enctypes than those requested by this attribute.

sync

This attribute is intended to set a list of external systems with which data about this keytab is synchronized, but there are no supported targets currently. However, there is support for clearing this attribute or returning its current value.

If no other arguments besides ATTRIBUTE are given, returns the values of that attribute, if any, as a list. On error, returns the empty list. To distinguish between an error and an empty return, call error() afterward. It is guaranteed to return undef unless there was an error.

If other arguments are given, sets the given ATTRIBUTE values to VALUES, which must be a reference to an array (even if only one value is being set). Pass a reference to an empty array to clear the attribute values. PRINCIPAL, HOSTNAME, and DATETIME are stored as history information. PRINCIPAL should be the user who is destroying the object. If DATETIME isn't given, the current time is used.

create(TYPE, NAME, DBH, PRINCIPAL, HOSTNAME [, DATETIME])

This is a class method and should be called on the Wallet::Object::Keytab class. It creates a new object with the given TYPE and NAME (TYPE is normally keytab and must be for the rest of the wallet system to use the right class, but this module doesn't check for ease of subclassing), using DBH as the handle to the wallet metadata database. PRINCIPAL, HOSTNAME, and DATETIME are stored as history information. PRINCIPAL should be the user who is creating the object. If DATETIME isn't given, the current time is used.

When a new keytab object is created, the Kerberos principal designated by NAME is also created in the Kerberos realm determined from the wallet configuration. If the principal already exists, create() still succeeds (so that a previously unmanaged principal can be imported into the wallet). Otherwise, if the Kerberos principal could not be created, create() fails. The principal is created with the randomized keys. NAME must not contain the realm; instead, the KEYTAB_REALM configuration variable should be set. See Wallet::Config for more information.

If create() fails, it throws an exception.

destroy(PRINCIPAL, HOSTNAME [, DATETIME])

Destroys a keytab object by removing it from the database and deleting the principal out of Kerberos. If deleting the principal fails, destroy() fails, but destroy() succeeds if the principal didn't exist when it was called (so that it can be used to clean up stranded entries). Returns true on success and false on failure. The caller should call error() to get the error message after a failure. PRINCIPAL, HOSTNAME, and DATETIME are stored as history information. PRINCIPAL should be the user who is destroying the object. If DATETIME isn't given, the current time is used.

get(PRINCIPAL, HOSTNAME [, DATETIME])

Retrieves a keytab for this object and returns the keytab data or undef on error. The caller should call error() to get the error message if get() returns undef. The keytab is created with new randomized keys, invalidating any existing keytabs for that principal, unless the unchanging flag is set on the object. PRINCIPAL, HOSTNAME, and DATETIME are stored as history information. PRINCIPAL should be the user who is downloading the keytab. If DATETIME isn't given, the current time is used.

FILES

KEYTAB_TMP/keytab.<pid>

The keytab is created in this file and then read into memory. KEYTAB_TMP is set in the wallet configuration, and <pid> is the process ID of the current process. The file is unlinked after being read.

LIMITATIONS

Only one Kerberos realm is supported for a given wallet implementation and all keytab objects stored must be in that realm. Keytab names in the wallet database do not have realm information.

SEE ALSO

kadmin(8), Wallet::Config(3), Wallet::Object::Base(3), wallet-backend(8)

This module is part of the wallet system. The current version is available from <http://www.eyrie.org/~eagle/software/wallet/>.

AUTHOR

Russ Allbery <eagle@eyrie.org>

Last modified and spun 2016-01-24