javax.crypto
Class Mac

java.lang.Object
  |
  +--javax.crypto.Mac

public class Mac
extends Object

This class provides the functionality of a "message authentication code" (MAC).

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.


Constructor Summary
protected Mac(MacSpi macSpi, Provider provider, String algorithm)
          Creates a MAC object.
 
Method Summary
 Object clone()
          Returns a clone if the 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 standard name of the MAC algorithm.
static Mac getInstance(String algorithm)
          Generates an Mac object that implements the specified MAC algorithm.
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 the MAC with the given (secret) key.
 void init(Key key, AlgorithmParameterSpec params)
          Initializes the MAC with the given (secret) 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.
 
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 standard name of the MAC algorithm. See Appendix A in the Java Cryptography Extension API Specification & Reference for information about standard algorithm names.

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

Returns:
the standard algorithm name.

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 API Specification & Reference for information about standard algorithm names.
Returns:
the new Mac object.
Throws:
NoSuchAlgorithmException - if the requested MAC algorithm is not available.

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 API Specification & Reference for information about standard algorithm names.
provider - the provider
Returns:
the new Mac object.
Throws:
NoSuchAlgorithmException - if the requested MAC algorithm is not available.
NoSuchProviderException - if the requested provider is not available.

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 the MAC with the given (secret) key.
Parameters:
key - the (secret) 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 the MAC with the given (secret) key and algorithm parameters.
Parameters:
key - the (secret) 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.
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).

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 Object clone()
             throws CloneNotSupportedException
Returns a clone if the implementation is cloneable.
Overrides:
clone in class Object
Returns:
a clone if the implementation is cloneable.
Throws:
CloneNotSupportedException - if this is called on an implementation that does not support Cloneable.