JavaTM 2 Platform
Std. Ed. v1.4.2

javax.crypto
Class Mac

java.lang.Object
  extended byjavax.crypto.Mac
All Implemented Interfaces:
Cloneable

public class Mac
extends Object
implements Cloneable

This class provides the functionality of a "Message Authentication Code" (MAC) algorithm.

A MAC provides a way to check the integrity of information transmitted over or stored in an unreliable medium, based on a secret key. Typically, message authentication codes are used between two parties that share a secret key in order to validate information transmitted between these parties.

A MAC mechanism that is based on cryptographic hash functions is referred to as HMAC. HMAC can be used with any cryptographic hash function, e.g., MD5 or SHA-1, in combination with a secret shared key. HMAC is specified in RFC 2104.

Since:
1.4

Constructor Summary
protected Mac(MacSpi macSpi, Provider provider, String algorithm)
          Creates a MAC object.
 
Method Summary
 Object clone()
          Returns a clone if the provider implementation is cloneable.
 byte[] doFinal()
          Finishes the MAC operation.
 byte[] doFinal(byte[] input)
          Processes the given array of bytes and finishes the MAC operation.
 void doFinal(byte[] output, int outOffset)
          Finishes the MAC operation.
 String getAlgorithm()
          Returns the algorithm name of this Mac object.
static Mac getInstance(String algorithm)
          Generates an Mac object that implements the specified MAC algorithm.
static Mac getInstance(String algorithm, Provider provider)
          Generates an Mac object for the specified MAC algorithm from the specified provider.
static Mac getInstance(String algorithm, String provider)
          Generates an Mac object for the specified MAC algorithm from the specified provider.
 int getMacLength()
          Returns the length of the MAC in bytes.
 Provider getProvider()
          Returns the provider of this Mac object.
 void init(Key key)
          Initializes this Mac object with the given key.
 void init(Key key, AlgorithmParameterSpec params)
          Initializes this Mac object with the given key and algorithm parameters.
 void reset()
          Resets this Mac object.
 void update(byte input)
          Processes the given byte.
 void update(byte[] input)
          Processes the given array of bytes.
 void update(byte[] input, int offset, int len)
          Processes the first len bytes in input, starting at offset inclusive.
 
Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Mac

protected Mac(MacSpi macSpi,
              Provider provider,
              String algorithm)
Creates a MAC object.

Parameters:
macSpi - the delegate
provider - the provider
algorithm - the algorithm
Method Detail

getAlgorithm

public final String getAlgorithm()
Returns the algorithm name of this Mac object.

This is the same name that was specified in one of the getInstance calls that created this Mac object.

Returns:
the algorithm name of this Mac object.

getInstance

public static final Mac getInstance(String algorithm)
                             throws NoSuchAlgorithmException
Generates an Mac object that implements the specified MAC algorithm. If the default provider package provides an implementation of the requested MAC algorithm, an instance of Mac containing that implementation is returned. If the algorithm is not available in the default provider package, other provider packages are searched.

Parameters:
algorithm - the standard name of the requested MAC algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.
Returns:
the new Mac object.
Throws:
NoSuchAlgorithmException - if the specified algorithm is not available in the default provider package or any of the other provider packages that were searched.

getInstance

public static final Mac getInstance(String algorithm,
                                    String provider)
                             throws NoSuchAlgorithmException,
                                    NoSuchProviderException
Generates an Mac object for the specified MAC algorithm from the specified provider.

Parameters:
algorithm - the standard name of the requested MAC algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.
provider - the name of the provider.
Returns:
the new Mac object.
Throws:
NoSuchAlgorithmException - if the specified algorithm is not available from the specified provider.
NoSuchProviderException - if the specified provider has not been configured.
IllegalArgumentException - if the provider is null.

getInstance

public static final Mac getInstance(String algorithm,
                                    Provider provider)
                             throws NoSuchAlgorithmException
Generates an Mac object for the specified MAC algorithm from the specified provider. Note: the provider doesn't have to be registered.

Parameters:
algorithm - the standard name of the requested MAC algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.
provider - the name of the provider.
Returns:
the new Mac object.
Throws:
NoSuchAlgorithmException - if the specified algorithm is not available from the specified provider.
IllegalArgumentException - if the provider is null.

getProvider

public final Provider getProvider()
Returns the provider of this Mac object.

Returns:
the provider of this Mac object.

getMacLength

public final int getMacLength()
Returns the length of the MAC in bytes.

Returns:
the MAC length in bytes.

init

public final void init(Key key)
                throws InvalidKeyException
Initializes this Mac object with the given key.

Parameters:
key - the key.
Throws:
InvalidKeyException - if the given key is inappropriate for initializing this MAC.

init

public final void init(Key key,
                       AlgorithmParameterSpec params)
                throws InvalidKeyException,
                       InvalidAlgorithmParameterException
Initializes this Mac object with the given key and algorithm parameters.

Parameters:
key - the key.
params - the algorithm parameters.
Throws:
InvalidKeyException - if the given key is inappropriate for initializing this MAC.
InvalidAlgorithmParameterException - if the given algorithm parameters are inappropriate for this MAC.

update

public final void update(byte input)
                  throws IllegalStateException
Processes the given byte.

Parameters:
input - the input byte to be processed.
Throws:
IllegalStateException - if this Mac has not been initialized.

update

public final void update(byte[] input)
                  throws IllegalStateException
Processes the given array of bytes.

Parameters:
input - the array of bytes to be processed.
Throws:
IllegalStateException - if this Mac has not been initialized.

update

public final void update(byte[] input,
                         int offset,
                         int len)
                  throws IllegalStateException
Processes the first len bytes in input, starting at offset inclusive.

Parameters:
input - the input buffer.
offset - the offset in input where the input starts.
len - the number of bytes to process.
Throws:
IllegalStateException - if this Mac has not been initialized.

doFinal

public final byte[] doFinal()
                     throws IllegalStateException
Finishes the MAC operation.

A call to this method resets this Mac object to the state it was in when previously initialized via a call to init(Key) or init(Key, AlgorithmParameterSpec). That is, the object is reset and available to generate another MAC from the same key, if desired, via new calls to update and doFinal. (In order to reuse this Mac object with a different key, it must be reinitialized via a call to init(Key) or init(Key, AlgorithmParameterSpec).

Returns:
the MAC result.
Throws:
IllegalStateException - if this Mac has not been initialized.

doFinal

public final void doFinal(byte[] output,
                          int outOffset)
                   throws ShortBufferException,
                          IllegalStateException
Finishes the MAC operation.

A call to this method resets this Mac object to the state it was in when previously initialized via a call to init(Key) or init(Key, AlgorithmParameterSpec). That is, the object is reset and available to generate another MAC from the same key, if desired, via new calls to update and doFinal. (In order to reuse this Mac object with a different key, it must be reinitialized via a call to init(Key) or init(Key, AlgorithmParameterSpec).

The MAC result is stored in output, starting at outOffset inclusive.

Parameters:
output - the buffer where the MAC result is stored
outOffset - the offset in output where the MAC is stored
Throws:
ShortBufferException - if the given output buffer is too small to hold the result
IllegalStateException - if this Mac has not been initialized.

doFinal

public final byte[] doFinal(byte[] input)
                     throws IllegalStateException
Processes the given array of bytes and finishes the MAC operation.

A call to this method resets this Mac object to the state it was in when previously initialized via a call to init(Key) or init(Key, AlgorithmParameterSpec). That is, the object is reset and available to generate another MAC from the same key, if desired, via new calls to update and doFinal. (In order to reuse this Mac object with a different key, it must be reinitialized via a call to init(Key) or init(Key, AlgorithmParameterSpec).

Parameters:
input - data in bytes
Returns:
the MAC result.
Throws:
IllegalStateException - if this Mac has not been initialized.

reset

public final void reset()
Resets this Mac object.

A call to this method resets this Mac object to the state it was in when previously initialized via a call to init(Key) or init(Key, AlgorithmParameterSpec). That is, the object is reset and available to generate another MAC from the same key, if desired, via new calls to update and doFinal. (In order to reuse this Mac object with a different key, it must be reinitialized via a call to init(Key) or init(Key, AlgorithmParameterSpec).


clone

public final Object clone()
                   throws CloneNotSupportedException
Returns a clone if the provider implementation is cloneable.

Overrides:
clone in class Object
Returns:
a clone if the provider implementation is cloneable.
Throws:
CloneNotSupportedException - if this is called on a delegate that does not support Cloneable.
See Also:
Cloneable

JavaTM 2 Platform
Std. Ed. v1.4.2

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.


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