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javax.crypto

Class Mac

Implemented Interfaces:
Cloneable
public class Mac
extends Object
implements Cloneable
This class implements a "message authentication code" (MAC), a method to ensure the integrity of data transmitted between two parties who share a common secret key.

The best way to describe a MAC is as a keyed one-way hash function, which looks like:

D = MAC(K, M)

where K is the key, M is the message, and D is the resulting digest. One party will usually send the concatenation M || D to the other party, who will then verify D by computing D' in a similar fashion. If D == D', then the message is assumed to be authentic.

Constructor Summary

Mac(MacSpi macSpi, Provider provider, String algorithm)
Creates a new Mac instance.

Method Summary

Object
clone()
Clone this instance, if the underlying implementation supports it.
byte[]
doFinal()
Finishes the computation of a MAC and returns the digest.
byte[]
doFinal(byte[] input)
Finishes the computation of a MAC with a final byte array (or computes a MAC over those bytes only) and returns the digest.
void
doFinal(byte[] output, int outOffset)
Finishes the computation of a MAC and places the result into the given array.
String
getAlgorithm()
Returns the name of this MAC algorithm.
static Mac
getInstance(String algorithm)
Create an instance of the named algorithm from the first provider with an appropriate implementation.
static Mac
getInstance(String algorithm, String provider)
Create an instance of the named algorithm from the named provider.
static Mac
getInstance(String algorithm, Provider provider)
Create an instance of the named algorithm from a provider.
int
getMacLength()
Get the size of the MAC.
Provider
getProvider()
Get the provider of the underlying implementation.
void
init(Key key)
Initialize this MAC with a key and no parameters.
void
init(Key key, AlgorithmParameterSpec params)
Initialize this MAC with a key and parameters.
void
reset()
Reset this instance.
void
update(byte input)
Update the computation with a single byte.
void
update(byte[] input)
Update the computation with a byte array.
void
update(byte[] input, int offset, int length)
Update the computation with a portion of a byte array.
void
update(ByteBuffer buffer)
Update this MAC with the remaining bytes in the given buffer

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Mac

protected Mac(MacSpi macSpi,
              Provider provider,
              String algorithm)
Creates a new Mac instance.
Parameters:
macSpi - The underlying MAC implementation.
provider - The provider of this implementation.
algorithm - The name of this MAC algorithm.

Method Details

clone

public final Object clone()
            throws CloneNotSupportedException
Clone this instance, if the underlying implementation supports it.
Overrides:
clone in interface Object
Returns:
A clone of this instance.
Throws:
CloneNotSupportedException - If the underlying implementation is not cloneable.

doFinal

public final byte[] doFinal()
            throws IllegalStateException
Finishes the computation of a MAC and returns the digest.

After this method succeeds, it may be used again as just after a call to init, and can compute another MAC using the same key and parameters.

Returns:
The message authentication code.
Throws:
IllegalStateException - If this instnace has not been initialized.

doFinal

public final byte[] doFinal(byte[] input)
            throws IllegalStateException
Finishes the computation of a MAC with a final byte array (or computes a MAC over those bytes only) and returns the digest.

After this method succeeds, it may be used again as just after a call to init, and can compute another MAC using the same key and parameters.

Parameters:
input - The bytes to add.
Returns:
The message authentication code.
Throws:
IllegalStateException - If this instnace has not been initialized.

doFinal

public final void doFinal(byte[] output,
                          int outOffset)
            throws IllegalStateException,
                   ShortBufferException
Finishes the computation of a MAC and places the result into the given array.

After this method succeeds, it may be used again as just after a call to init, and can compute another MAC using the same key and parameters.

Parameters:
output - The destination for the result.
outOffset - The index in the output array to start.
Throws:
IllegalStateException - If this instnace has not been initialized.
ShortBufferException - If output is not large enough to hold the result.

getAlgorithm

public final String getAlgorithm()
Returns the name of this MAC algorithm.
Returns:
The MAC name.

getInstance

public static final Mac getInstance(String algorithm)
            throws NoSuchAlgorithmException
Create an instance of the named algorithm from the first provider with an appropriate implementation.
Parameters:
algorithm - The name of the algorithm.
Returns:
An appropriate Mac instance, if the specified algorithm is implemented by a provider.
Throws:
NoSuchAlgorithmException - If no implementation of the named algorithm is installed.
IllegalArgumentException - if algorithm is null or is an empty string.

getInstance

public static final Mac getInstance(String algorithm,
                                    String provider)
            throws NoSuchAlgorithmException,
                   NoSuchProviderException
Create an instance of the named algorithm from the named provider.
Parameters:
algorithm - The name of the algorithm.
provider - The name of the provider.
Returns:
An appropriate Mac instance, if the specified algorithm is implemented by the named provider.
Throws:
NoSuchAlgorithmException - If the named provider has no implementation of the algorithm.
NoSuchProviderException - If the named provider does not exist.
IllegalArgumentException - if either algorithm or provider is null, or if algorithm is an empty string.

getInstance

public static final Mac getInstance(String algorithm,
                                    Provider provider)
            throws NoSuchAlgorithmException
Create an instance of the named algorithm from a provider.
Parameters:
algorithm - The name of the algorithm.
provider - The provider.
Returns:
An appropriate Mac instance, if the specified algorithm is implemented by the provider.
Throws:
NoSuchAlgorithmException - If the provider has no implementation of the algorithm.
IllegalArgumentException - if either algorithm or provider is null, or if algorithm is an empty string.

getMacLength

public final int getMacLength()
Get the size of the MAC. This is the size of the array returned by doFinal() and doFinal(byte[]), and the minimum number of bytes that must be available in the byte array passed to doFinal(byte[],int).
Returns:
The MAC length.

getProvider

public final Provider getProvider()
Get the provider of the underlying implementation.
Returns:
The provider.

init

public final void init(Key key)
            throws InvalidKeyException
Initialize this MAC with a key and no parameters.
Parameters:
key - The key to initialize this instance with.
Throws:
InvalidKeyException - If the key is unacceptable.

init

public final void init(Key key,
                       AlgorithmParameterSpec params)
            throws InvalidAlgorithmParameterException,
                   InvalidKeyException
Initialize this MAC with a key and parameters.
Parameters:
key - The key to initialize this instance with.
params - The algorithm-specific parameters.
Throws:
InvalidAlgorithmParameterException - If the algorithm parameters are unacceptable.
InvalidKeyException - If the key is unacceptable.

reset

public final void reset()
Reset this instance. A call to this method returns this instance back to the state it was in just after it was initialized.

update

public final void update(byte input)
            throws IllegalStateException
Update the computation with a single byte.
Parameters:
input - The next byte.
Throws:
IllegalStateException - If this instance has not been initialized.

update

public final void update(byte[] input)
            throws IllegalStateException
Update the computation with a byte array.
Parameters:
input - The next bytes.
Throws:
IllegalStateException - If this instance has not been initialized.

update

public final void update(byte[] input,
                         int offset,
                         int length)
            throws IllegalStateException
Update the computation with a portion of a byte array.
Parameters:
input - The next bytes.
offset - The index in input to start.
length - The number of bytes to update.
Throws:
IllegalStateException - If this instance has not been initialized.

update

public final void update(ByteBuffer buffer)
Update this MAC with the remaining bytes in the given buffer
Parameters:
buffer - The input buffer.
Since:
1.5
Mac.java -- The message authentication code interface. Copyright (C) 2004 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.

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