Mac

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.

Android provides the following Mac algorithms

Name Supported (API Levels)
DESedeMAC 1–8
DESedeMAC/CFB8 1–8
DESedeMAC64 1–8
DESMAC 1–8
DESMAC/CFB8 1–8
DESwithISO9797 1–8
HmacMD5 1+
HmacSHA1 1+
HmacSHA224 1–8, 22+
HmacSHA256 1+
HmacSHA384 1+
HmacSHA512 1+
ISO9797ALG3MAC 1–8
PBEwithHmacSHA 1+
PBEwithHmacSHA1 1+
These algorithms are described in the Mac section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

Protected Constructor Summary

Mac(MacSpi macSpi, Provider provider, String algorithm)
Creates a MAC object.

Public Method Summary

final Object
clone()
Returns a clone if the provider implementation is cloneable.
final byte[]
doFinal(byte[] input)
Processes the given array of bytes and finishes the MAC operation.
final void
doFinal(byte[] output, int outOffset)
Finishes the MAC operation.
final byte[]
doFinal()
Finishes the MAC operation.
final String
getAlgorithm()
Returns the algorithm name of this Mac object.
final static Mac
getInstance(String algorithm)
Returns a Mac object that implements the specified MAC algorithm.
final static Mac
getInstance(String algorithm, String provider)
Returns a Mac object that implements the specified MAC algorithm.
final static Mac
getInstance(String algorithm, Provider provider)
Returns a Mac object that implements the specified MAC algorithm.
final int
getMacLength()
Returns the length of the MAC in bytes.
final Provider
getProvider()
Returns the provider of this Mac object.
final void
init(Key key, AlgorithmParameterSpec params)
Initializes this Mac object with the given key and algorithm parameters.
final void
init(Key key)
Initializes this Mac object with the given key.
final void
reset()
Resets this Mac object.
final void
update(byte[] input)
Processes the given array of bytes.
final void
update(byte[] input, int offset, int len)
Processes the first len bytes in input, starting at offset inclusive.
final void
update(ByteBuffer input)
Processes input.remaining() bytes in the ByteBuffer input, starting at input.position().
final void
update(byte input)
Processes the given byte.

Inherited Method Summary

Protected Constructors

protected Mac (MacSpi macSpi, Provider provider, String algorithm)

Creates a MAC object.

Parameters
macSpi the delegate
provider the provider
algorithm the algorithm

Public Methods

public final Object clone ()

Returns a clone if the provider implementation is cloneable.

Returns
  • a clone if the provider implementation is cloneable.
Throws
CloneNotSupportedException if this is called on a delegate that does not support Cloneable.

public final byte[] doFinal (byte[] input)

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.

public final void doFinal (byte[] output, int outOffset)

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.

public final byte[] doFinal ()

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.

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.

public static final Mac getInstance (String algorithm)

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.

Parameters
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.
Returns
  • the new Mac object.
Throws
NoSuchAlgorithmException if no Provider supports a MacSpi implementation for the specified algorithm.
See Also

public static final Mac getInstance (String algorithm, String provider)

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 Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
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.
See Also

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

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 Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider the provider.
Returns
  • the new Mac object.
Throws
NoSuchAlgorithmException if a MacSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException if the provider is null.
See Also

public final int getMacLength ()

Returns the length of the MAC in bytes.

Returns
  • the MAC length in bytes.

public final Provider getProvider ()

Returns the provider of this Mac object.

Returns
  • the provider of this Mac object.

public final void init (Key key, AlgorithmParameterSpec params)

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.

public final void init (Key key)

Initializes this Mac object with the given key.

Parameters
key the key.
Throws
InvalidKeyException if the given key is inappropriate for initializing this MAC.

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 void update (byte[] input)

Processes the given array of bytes.

Parameters
input the array of bytes to be processed.
Throws
IllegalStateException if this Mac has not been initialized.

public final void update (byte[] input, int offset, int len)

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.

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.

public final void update (byte input)

Processes the given byte.

Parameters
input the input byte to be processed.
Throws
IllegalStateException if this Mac has not been initialized.