javax.crypto

Class Mac

java.lang.Object

javax.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.

Every implementation of the Java platform is required to support the following standard Mac algorithms:

• HmacMD5
• HmacSHA1
• HmacSHA256

These algorithms are described in the Mac Algorithms section of the Java Security Standard Algorithm Names Specification. Consult the release documentation for your implementation to see if any other algorithms are supported.

Since:

1.4

Author:

Jan Luehe

Method Summary

Modifier and Type	Method and Description
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) Returns a Mac object that implements the specified MAC algorithm.
static Mac	getInstance(String algorithm, String provider) Returns a Mac object that implements the specified MAC algorithm.
int	getMacLength() Returns the length of the MAC in bytes.
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, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

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

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 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.

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.

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

Returns a Mac object that implements the specified MAC algorithm.

This method traverses the list of registered security Providers, starting with the most preferred Provider. A new Mac object encapsulating the MacSpi implementation from the first Provider that supports the specified algorithm is returned.

Parameters:

algorithm - the standard name of the requested MAC algorithm. See the Mac Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names. Consult the release documentation for your implementation to see which algorithms are supported.

Returns:

the new Mac object.

Throws:

NoSuchAlgorithmException - if no Provider supports a MacSpi implementation for the specified algorithm.

getInstance

public static final Mac getInstance(String algorithm,
                                    String provider)
                             throws NoSuchAlgorithmException,
                                    NoSuchProviderException

Returns a Mac object that implements the specified MAC algorithm.

A new Mac object encapsulating the MacSpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.

Parameters:

algorithm - the standard name of the requested MAC algorithm. See the Mac Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names. Consult the release documentation for your implementation to see which algorithms are supported.

provider - the name of the provider.

Returns:

the new Mac object.

Throws:

NoSuchAlgorithmException - if a MacSpi implementation for the specified algorithm is not available from the specified provider.

NoSuchProviderException - if the specified provider is not registered in the security provider list.

IllegalArgumentException - if the provider is null or empty.

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.

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).

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.