Class KeyTab


public final class KeyTab
extends Object

This class encapsulates a keytab file.

A Kerberos JAAS login module that obtains long term secret keys from a keytab file should use this class. The login module will store an instance of this class in the private credential set of a Subject during the commit phase of the authentication process.

If a KeyTab object is obtained from getUnboundInstance() or getUnboundInstance(java.io.File), it is unbound and thus can be used by any service principal. Otherwise, if it's obtained from getInstance(KerberosPrincipal) or getInstance(KerberosPrincipal, java.io.File), it is bound to the specific service principal and can only be used by it.

Please note the constructors getInstance() and getInstance(java.io.File) were created when there was no support for unbound keytabs. These methods should not be used anymore. An object created with either of these methods are considered to be bound to an unknown principal, which means, its isBound() returns true and getPrincipal() returns null.

It might be necessary for the application to be granted a PrivateCredentialPermission if it needs to access the KeyTab instance from a Subject. This permission is not needed when the application depends on the default JGSS Kerberos mechanism to access the KeyTab. In that case, however, the application will need an appropriate ServicePermission.

The keytab file format is described at http://www.ioplex.com/utilities/keytab.txt.

Since:
1.7

Methods

Modifier and Type Method and Description
boolean equals(Object other)

Compares the specified Object with this KeyTab for equality.
boolean exists()

Checks if the keytab file exists.
static KeyTab getInstance()

Returns the default KeyTab instance that is bound to an unknown service principal.
static KeyTab getInstance(File file)

Returns a KeyTab instance from a File object that is bound to an unknown service principal.
static KeyTab getInstance(KerberosPrincipal princ)

Returns the default KeyTab instance that is bound to the specified service principal.
static KeyTab getInstance(KerberosPrincipal princ, File file)

Returns a KeyTab instance from a File object that is bound to the specified service principal.
KerberosKey[] getKeys(KerberosPrincipal principal)

Returns fresh keys for the given Kerberos principal.
KerberosPrincipal getPrincipal()

Returns the service principal this KeyTab object is bound to.
static KeyTab getUnboundInstance()

Returns the default unbound KeyTab instance.
static KeyTab getUnboundInstance(File file)

Returns an unbound KeyTab instance from a File object.
int hashCode()

Returns a hashcode for this KeyTab.
boolean isBound()

Returns if the keytab is bound to a principal
String toString()

Returns a string representation of the object.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods

getInstance

public static KeyTab getInstance(File file)

Returns a KeyTab instance from a File object that is bound to an unknown service principal.

The result of this method is never null. This method only associates the returned KeyTab object with the file and does not read it.

Developers should call getInstance(KerberosPrincipal,File) when the bound service principal is known.

Parameters:
file - the keytab File object, must not be null
Returns:
the keytab instance
Throws:
NullPointerException - if the file argument is null

getUnboundInstance

public static KeyTab getUnboundInstance(File file)

Returns an unbound KeyTab instance from a File object.

The result of this method is never null. This method only associates the returned KeyTab object with the file and does not read it.

Parameters:
file - the keytab File object, must not be null
Returns:
the keytab instance
Throws:
NullPointerException - if the file argument is null
Since:
1.8

getInstance

public static KeyTab getInstance(KerberosPrincipal princ,
                                 File file)

Returns a KeyTab instance from a File object that is bound to the specified service principal.

The result of this method is never null. This method only associates the returned KeyTab object with the file and does not read it.

Parameters:
princ - the bound service principal, must not be null
file - the keytab File object, must not be null
Returns:
the keytab instance
Throws:
NullPointerException - if either of the arguments is null
Since:
1.8

getInstance

public static KeyTab getInstance()

Returns the default KeyTab instance that is bound to an unknown service principal.

The result of this method is never null. This method only associates the returned KeyTab object with the default keytab file and does not read it.

Developers should call getInstance(KerberosPrincipal) when the bound service principal is known.

Returns:
the default keytab instance.

getUnboundInstance

public static KeyTab getUnboundInstance()

Returns the default unbound KeyTab instance.

The result of this method is never null. This method only associates the returned KeyTab object with the default keytab file and does not read it.

Returns:
the default keytab instance
Since:
1.8

getInstance

public static KeyTab getInstance(KerberosPrincipal princ)

Returns the default KeyTab instance that is bound to the specified service principal.

The result of this method is never null. This method only associates the returned KeyTab object with the default keytab file and does not read it.

Parameters:
princ - the bound service principal, must not be null
Returns:
the default keytab instance
Throws:
NullPointerException - if princ is null
Since:
1.8

getKeys

public KerberosKey[] getKeys(KerberosPrincipal principal)

Returns fresh keys for the given Kerberos principal.

Implementation of this method should make sure the returned keys match the latest content of the keytab file. The result is a newly created copy that can be modified by the caller without modifying the keytab object. The caller should destroy the result keys after they are used.

Please note that the keytab file can be created after the KeyTab object is instantiated and its content may change over time. Therefore, an application should call this method only when it needs to use the keys. Any previous result from an earlier invocation could potentially be expired.

If there is any error (say, I/O error or format error) during the reading process of the KeyTab file, a saved result should be returned. If there is no saved result (say, this is the first time this method is called, or, all previous read attempts failed), an empty array should be returned. This can make sure the result is not drastically changed during the (probably slow) update of the keytab file.

Each time this method is called and the reading of the file succeeds with no exception (say, I/O error or file format error), the result should be saved for principal. The implementation can also save keys for other principals having keys in the same keytab object if convenient.

Any unsupported key read from the keytab is ignored and not included in the result.

If this keytab is bound to a specific principal, calling this method on another principal will return an empty array.

Parameters:
principal - the Kerberos principal, must not be null.
Returns:
the keys (never null, may be empty)
Throws:
NullPointerException - if the principal argument is null
SecurityException - if a security manager exists and the read access to the keytab file is not permitted

exists

public boolean exists()

Checks if the keytab file exists. Implementation of this method should make sure that the result matches the latest status of the keytab file.

The caller can use the result to determine if it should fallback to another mechanism to read the keys.

Returns:
true if the keytab file exists; false otherwise.
Throws:
SecurityException - if a security manager exists and the read access to the keytab file is not permitted

toString

public String toString()

Description copied from class: Object

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of: 

getClass().getName() + '@' + Integer.toHexString(hashCode())
Overrides:
toString in class Object
Returns:
a string representation of the object.

hashCode

public int hashCode()

Returns a hashcode for this KeyTab.

Overrides:
hashCode in class Object
Returns:
a hashCode() for the KeyTab
See Also:
Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

equals

public boolean equals(Object other)

Compares the specified Object with this KeyTab for equality. Returns true if the given object is also a KeyTab and the two KeyTab instances are equivalent.

Overrides:
equals in class Object
Parameters:
other - the Object to compare to
Returns:
true if the specified object is equal to this KeyTab
See Also:
Object.hashCode(), HashMap

getPrincipal

public KerberosPrincipal getPrincipal()

Returns the service principal this KeyTab object is bound to. Returns null if it's not bound.

Please note the deprecated constructors create a KeyTab object bound for some unknown principal. In this case, this method also returns null. User can call isBound() to verify this case.

Returns:
the service principal
Since:
1.8

isBound

public boolean isBound()

Returns if the keytab is bound to a principal

Returns:
if the keytab is bound to a principal
Since:
1.8

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https://docs.oracle.com/javase/8/docs/api/javax/security/auth/kerberos/KeyTab.html