public class

CMac

extends Object
implements Mac
java.lang.Object
   ↳ org.bouncycastle.crypto.macs.CMac

Class Overview

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.

Summary

Public Constructors
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.
Public Methods
int doFinal(byte[] out, int outOff)
Compute the final stage of the MAC writing the output to the out parameter.
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, int inOff, int len)
void update(byte in)
add a single byte to the mac for processing.
[Expand]
Inherited Methods
From class java.lang.Object
From interface org.bouncycastle.crypto.Mac

Public Constructors

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.

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.

Public Methods

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

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.

Parameters
out the array the MAC is to be output to.
outOff the offset into the out buffer the output is to start at.

public String getAlgorithmName ()

Return the name of the algorithm the MAC implements.

Returns
  • the name of the algorithm the MAC implements.

public int getMacSize ()

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

Returns
  • the block size for this MAC in bytes.

public void init (CipherParameters params)

Initialise the MAC.

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

public void reset ()

Reset the mac generator.

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

public void update (byte in)

add a single byte to the mac for processing.

Parameters
in the byte to be processed.