org.spongycastle.crypto.macs

Class GMac

java.lang.Object

org.spongycastle.crypto.macs.GMac

All Implemented Interfaces:

Mac

public class GMac
extends java.lang.Object
implements Mac

The GMAC specialisation of Galois/Counter mode (GCM) detailed in NIST Special Publication 800-38D.

GMac is an invocation of the GCM mode where no data is encrypted (i.e. all input data to the Mac is processed as additional authenticated data with the underlying GCM block cipher).

Constructor Summary

Constructors

Constructor and Description
GMac(GCMBlockCipher cipher) Creates a GMAC based on the operation of a block cipher in GCM mode.
GMac(GCMBlockCipher cipher, int macSizeBits) Creates a GMAC based on the operation of a 128 bit block cipher in GCM mode.

Method Summary

Modifier and Type	Method and Description
int	doFinal(byte[] out, int outOff) Compute the final stage of the MAC writing the output to the out parameter.
java.lang.String	getAlgorithmName() Return the name of the algorithm the MAC implements.
int	getMacSize() Return the block size for this MAC (in bytes).
void	init(CipherParameters params) Initialises the GMAC - requires a ParametersWithIV providing a KeyParameter and a nonce.
void	reset() Reset the MAC.
void	update(byte in) add a single byte to the mac for processing.
void	update(byte[] in, int inOff, int len)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GMac

public GMac(GCMBlockCipher cipher)

Creates a GMAC based on the operation of a block cipher in GCM mode.

This will produce an authentication code the length of the block size of the cipher.

Parameters:

cipher - the cipher to be used in GCM mode to generate the MAC.

GMac

public GMac(GCMBlockCipher cipher,
            int macSizeBits)

Creates a GMAC based on the operation of a 128 bit block cipher in GCM mode.

Parameters:

macSizeBits - the mac size to generate, in bits. Must be a multiple of 8 and >= 32 and <= 128. Sizes less than 96 are not recommended, but are supported for specialized applications.

cipher - the cipher to be used in GCM mode to generate the MAC.

Method Detail

init

public void init(CipherParameters params)
          throws java.lang.IllegalArgumentException

Initialises the GMAC - requires a ParametersWithIV providing a KeyParameter and a nonce.

Specified by:

init in interface Mac

Parameters:

params - the key and other data required by the MAC.

Throws:

java.lang.IllegalArgumentException - if the params argument is inappropriate.

getAlgorithmName

public java.lang.String getAlgorithmName()

Description copied from interface: Mac

Return the name of the algorithm the MAC implements.

Specified by:

getAlgorithmName in interface Mac

Returns:

the name of the algorithm the MAC implements.

getMacSize

public int getMacSize()

Description copied from interface: Mac

Return the block size for this MAC (in bytes).

Specified by:

getMacSize in interface Mac

Returns:

the block size for this MAC in bytes.

update

public void update(byte in)
            throws java.lang.IllegalStateException

Description copied from interface: Mac

add a single byte to the mac for processing.

Specified by:

update in interface Mac

Parameters:

in - the byte to be processed.

Throws:

java.lang.IllegalStateException - if the MAC is not initialised.

update

public void update(byte[] in,
                   int inOff,
                   int len)
            throws DataLengthException,
                   java.lang.IllegalStateException

Specified by:

update in interface Mac

Parameters:

in - the array containing the input.

inOff - the index in the array the data begins at.

len - the length of the input starting at inOff.

Throws:

DataLengthException - if there isn't enough data in in.

java.lang.IllegalStateException - if the MAC is not initialised.

doFinal

public int doFinal(byte[] out,
                   int outOff)
            throws DataLengthException,
                   java.lang.IllegalStateException

Description copied from interface: Mac

Compute the final stage of the MAC writing the output to the out parameter.

doFinal leaves the MAC in the same state it was after the last init.

Specified by:

doFinal in interface Mac

Parameters:

out - the array the MAC is to be output to.

outOff - the offset into the out buffer the output is to start at.

Throws:

DataLengthException - if there isn't enough space in out.

java.lang.IllegalStateException - if the MAC is not initialised.

reset

public void reset()

Description copied from interface: Mac

Reset the MAC. At the end of resetting the MAC should be in the in the same state it was after the last init (if there was one).

Specified by:

reset in interface Mac