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
protected Mac(MacSpi macSpi, Provider provider, String algorithm)
Creates a MAC object.
macSpi
- the delegateprovider
- the provideralgorithm
- the algorithmpublic 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.
Mac
object.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.
algorithm
- the standard name of the requested MAC algorithm. See the Mac section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.Mac
object.NoSuchAlgorithmException
- if no Provider supports a MacSpi implementation for the specified algorithm.Provider
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.
algorithm
- the standard name of the requested MAC algorithm. See the Mac section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.provider
- the name of the provider.Mac
object.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.Provider
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.
algorithm
- the standard name of the requested MAC algorithm. See the Mac section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.provider
- the provider.Mac
object.NoSuchAlgorithmException
- if a MacSpi implementation for the specified algorithm is not available from the specified Provider object.IllegalArgumentException
- if the provider
is null.Provider
public final Provider getProvider()
Returns the provider of this Mac
object.
Mac
object.public final int getMacLength()
Returns the length of the MAC in bytes.
public final void init(Key key) throws InvalidKeyException
Initializes this Mac
object with the given key.
key
- the key.InvalidKeyException
- if the given key is inappropriate for initializing this MAC.public final void init(Key key, AlgorithmParameterSpec params) throws InvalidKeyException, InvalidAlgorithmParameterException
Initializes this Mac
object with the given key and algorithm parameters.
key
- the key.params
- the algorithm parameters.InvalidKeyException
- if the given key is inappropriate for initializing this MAC.InvalidAlgorithmParameterException
- if the given algorithm parameters are inappropriate for this MAC.public final void update(byte input) throws IllegalStateException
Processes the given byte.
input
- the input byte to be processed.IllegalStateException
- if this Mac
has not been initialized.public final void update(byte[] input) throws IllegalStateException
Processes the given array of bytes.
input
- the array of bytes to be processed.IllegalStateException
- if this Mac
has not been initialized.public final void update(byte[] input, int offset, int len) throws IllegalStateException
Processes the first len
bytes in input
, starting at offset
inclusive.
input
- the input buffer.offset
- the offset in input
where the input starts.len
- the number of bytes to process.IllegalStateException
- if this Mac
has not been initialized.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.
input
- the ByteBufferIllegalStateException
- if this Mac
has not been initialized.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)
.
IllegalStateException
- if this Mac
has not been initialized.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.
output
- the buffer where the MAC result is storedoutOffset
- the offset in output
where the MAC is storedShortBufferException
- if the given output buffer is too small to hold the resultIllegalStateException
- if this Mac
has not been initialized.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)
.
input
- data in bytesIllegalStateException
- if this Mac
has not been initialized.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)
.
public final Object clone() throws CloneNotSupportedException
Returns a clone if the provider implementation is cloneable.
clone
in class Object
CloneNotSupportedException
- if this is called on a delegate that does not support Cloneable
.Cloneable
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