Package org.bouncycastle.crypto.macs

Class GMac

java.lang.Object
org.bouncycastle.crypto.macs.GMac
All Implemented Interfaces:
Mac
public class GMac extends 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 Details

    • GMac

      public GMac(GCMModeCipher 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(GCMModeCipher cipher, int macSizeBits)
      Creates a GMAC based on the operation of a 128 bit block cipher in GCM mode.
      Parameters:
      cipher - the cipher to be used in GCM mode to generate the MAC.
      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.

  • Method Details

    • init

      public void init(CipherParameters params) throws 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:
      IllegalArgumentException - if the params argument is inappropriate.

    • getAlgorithmName

      public 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 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:
      IllegalStateException - if the MAC is not initialised.

    • update

      public void update(byte[] in, int inOff, int len) throws DataLengthException, 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.
      IllegalStateException - if the MAC is not initialised.

    • doFinal

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