org.spongycastle.crypto.macs

Class CMac

java.lang.Object

org.spongycastle.crypto.macs.CMac

All Implemented Interfaces:

Mac

Direct Known Subclasses:

CMacWithIV

public class CMac
extends java.lang.Object
implements Mac

CMAC - as specified at www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html

CMAC is analogous to OMAC1 - see also en.wikipedia.org/wiki/CMAC

CMAC is a NIST recomendation - see csrc.nist.gov/CryptoToolkit/modes/800-38_Series_Publications/SP800-38B.pdf

CMAC/OMAC1 is a blockcipher-based message authentication code designed and analyzed by Tetsu Iwata and Kaoru Kurosawa.

CMAC/OMAC1 is a simple variant of the CBC MAC (Cipher Block Chaining Message Authentication Code). OMAC stands for One-Key CBC MAC.

It supports 128- or 64-bits block ciphers, with any key size, and returns a MAC with dimension less or equal to the block size of the underlying cipher.

Constructor Summary

Constructors

Constructor and Description
CMac(BlockCipher cipher) create a standard MAC based on a CBC block cipher (64 or 128 bit block).
CMac(BlockCipher cipher, int macSizeInBits) create a standard MAC based on a block cipher with the size of the MAC been given in bits.

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) Initialise the MAC.
void	reset() Reset the mac generator.
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

CMac

public CMac(BlockCipher cipher)

create a standard MAC based on a CBC block cipher (64 or 128 bit block). This will produce an authentication code the length of the block size of the cipher.

Parameters:

cipher - the cipher to be used as the basis of the MAC generation.

CMac

public CMac(BlockCipher cipher,
            int macSizeInBits)

create a standard MAC based on a block cipher with the size of the MAC been given in bits.

Note: the size of the MAC must be at least 24 bits (FIPS Publication 81), or 16 bits if being used as a data authenticator (FIPS Publication 113), and in general should be less than the size of the block cipher as it reduces the chance of an exhaustive attack (see Handbook of Applied Cryptography).

Parameters:

cipher - the cipher to be used as the basis of the MAC generation.

macSizeInBits - the size of the MAC in bits, must be a multiple of 8 and <= 128.

Method Detail

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.

init

public void init(CipherParameters params)

Description copied from interface: Mac

Initialise the MAC.

Specified by:

init in interface Mac

Parameters:

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

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)

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.

update

public void update(byte[] in,
                   int inOff,
                   int len)

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.

doFinal

public int doFinal(byte[] out,
                   int outOff)

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.

reset

public void reset()

Reset the mac generator.

Specified by:

reset in interface Mac