public class Mac extends Object implements Cloneable
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:
| Modifier | Constructor and Description |
|---|---|
protected |
Mac(MacSpi macSpi,
Provider provider,
String algorithm)
Creates a MAC object.
|
| 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,
Provider provider)
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.
|
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(). |
public final String getAlgorithm()
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
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.Providerpublic static final Mac getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
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.Providerpublic static final Mac getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
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.Providerpublic final Provider getProvider()
Mac object.Mac object.public final int getMacLength()
public final void init(Key key) throws InvalidKeyException
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
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
input - the input byte to be processed.IllegalStateException - if this Mac has not been
initialized.public final void update(byte[] input)
throws IllegalStateException
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
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)
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
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
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
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()
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
clone in class ObjectCloneNotSupportedException - if this is called on a
delegate that does not support Cloneable.Cloneable Submit a bug or feature
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