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javax.crypto
Class Mac  

java.lang.Object
  javax.crypto.Mac

All Implemented Interfaces:

java.lang.Cloneable

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public class Mac

extends java.lang.Object

implements java.lang.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.

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Field Summary
private  java.lang.String	algorithm           The name of the algorithm.
private  MacSpi	macSpi           The underlying MAC implementation.
private  java.security.Provider	provider           The provider we got our implementation from.
private static java.lang.String	SERVICE
private  boolean	virgin           Whether or not we've been initialized.

 

Constructor Summary
protected	Mac(MacSpi macSpi, java.security.Provider provider, java.lang.String algorithm)           Creates a new Mac instance.

 

Method Summary
java.lang.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.
java.lang.String	getAlgorithm()           Returns the name of this MAC algorithm.
static Mac	getInstance(java.lang.String algorithm)           Get an instance of the named algorithm from the first provider with an appropriate implementation.
static Mac	getInstance(java.lang.String algorithm, java.security.Provider provider)           Get an instance of the named algorithm from a provider.
static Mac	getInstance(java.lang.String algorithm, java.lang.String provider)           Get an instance of the named algorithm from the named provider.
int	getMacLength()           Get the size of the MAC.
java.security.Provider	getProvider()           Get the provider of the underlying implementation.
void	init(java.security.Key key)           Initialize this MAC with a key and no parameters.
void	init(java.security.Key key, java.security.spec.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.

 

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Field Detail

SERVICE

private static final java.lang.String SERVICE

See Also:

Constant Field Values

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macSpi

private MacSpi macSpi

The underlying MAC implementation.

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provider

private java.security.Provider provider

The provider we got our implementation from.

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algorithm

private java.lang.String algorithm

The name of the algorithm.

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virgin

private boolean virgin

Whether or not we've been initialized.

Constructor Detail

Mac

protected Mac(MacSpi macSpi,
              java.security.Provider provider,
              java.lang.String algorithm)

Creates a new Mac instance.

Method Detail

getInstance

public static final Mac getInstance(java.lang.String algorithm)
                             throws java.security.NoSuchAlgorithmException

Get an instance of the named algorithm from the first provider with an appropriate implementation.

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getInstance

public static final Mac getInstance(java.lang.String algorithm,
                                    java.lang.String provider)
                             throws java.security.NoSuchAlgorithmException,
                                    java.security.NoSuchProviderException

Get an instance of the named algorithm from the named provider.

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getInstance

public static final Mac getInstance(java.lang.String algorithm,
                                    java.security.Provider provider)
                             throws java.security.NoSuchAlgorithmException

Get an instance of the named algorithm from a provider.

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doFinal

public final byte[] doFinal()
                     throws java.lang.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.

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doFinal

public final byte[] doFinal(byte[] input)
                     throws java.lang.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.

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doFinal

public final void doFinal(byte[] output,
                          int outOffset)
                   throws java.lang.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.

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getAlgorithm

public final java.lang.String getAlgorithm()

Returns the name of this MAC algorithm.

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getMacLength

public final int getMacLength()

Get the size of the MAC. This is the size of the array returned by doFinal() 55 and doFinal(byte[]) 55 , and the minimum number of bytes that must be available in the byte array passed to doFinal(byte[],int) 55 .

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getProvider

public final java.security.Provider getProvider()

Get the provider of the underlying implementation.

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init

public final void init(java.security.Key key)
                throws java.security.InvalidKeyException

Initialize this MAC with a key and no parameters.

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init

public final void init(java.security.Key key,
                       java.security.spec.AlgorithmParameterSpec params)
                throws java.security.InvalidAlgorithmParameterException,
                       java.security.InvalidKeyException

Initialize this MAC with a key and parameters.

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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.

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update

public final void update(byte input)
                  throws java.lang.IllegalStateException

Update the computation with a single byte.

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update

public final void update(byte[] input)
                  throws java.lang.IllegalStateException

Update the computation with a byte array.

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update

public final void update(byte[] input,
                         int offset,
                         int length)
                  throws java.lang.IllegalStateException

Update the computation with a portion of a byte array.

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clone

public final java.lang.Object clone()
                             throws java.lang.CloneNotSupportedException

Clone this instance, if the underlying implementation supports it.

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