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., SHA256 or SHA384, 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 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

Constructor Summary

Constructors
Modifier	Constructor	Description
`protected`	`Mac(MacSpi macSpi, Provider provider, String algorithm)`	Creates a MAC object.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	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.
`static Mac`	`getInstance(String algorithm, Provider provider)`	Returns a `Mac` object that implements the specified MAC algorithm.
`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.
`void`	`update(ByteBuffer input)`	Processes `input.remaining()` bytes in the ByteBuffer `input`, starting at `input.position()`.

Methods declared in 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

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.

Note that the list of registered providers may be retrieved via the Security.getProviders() method.

Implementation Note:: The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().
Parameters:: algorithm - the standard name of the requested MAC algorithm. See the Mac section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
Returns:: the new Mac object
Throws:: NoSuchAlgorithmException - if no Provider supports a MacSpi implementation for the specified algorithm; NullPointerException - if algorithm is null
See Also:: Provider

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.

Note that the list of registered providers may be retrieved via the Security.getProviders() method.

Parameters:: algorithm - the standard name of the requested MAC algorithm. See the Mac section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.; provider - the name of the provider.
Returns:: the new Mac object
Throws:: IllegalArgumentException - if the provider is null or empty; 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; NullPointerException - if algorithm is null
See Also:: Provider

getInstance

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

Returns a Mac object that implements the specified MAC algorithm.

A new Mac object encapsulating the MacSpi implementation from the specified Provider object is returned. Note that the specified Provider object does not have to be registered in the provider list.

Parameters:: algorithm - the standard name of the requested MAC algorithm. See the Mac section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.; provider - the provider.
Returns:: the new Mac object
Throws:: IllegalArgumentException - if the provider is null; NoSuchAlgorithmException - if a MacSpi implementation for the specified algorithm is not available from the specified Provider object; NullPointerException - if algorithm is null
See Also:: Provider

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.

update

public final void update(ByteBuffer input)

Processes input.remaining() bytes in the ByteBuffer input, starting at input.position(). Upon return, the buffer's position will be equal to its limit; its limit will not have changed.

Parameters:: input - the ByteBuffer
Throws:: IllegalStateException - if this Mac has not been initialized.
Since:: 1.5

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