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package org.spongycastle.crypto.macs;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.DataLengthException;
import org.spongycastle.crypto.InvalidCipherTextException;
import org.spongycastle.crypto.Mac;
import org.spongycastle.crypto.modes.GCMBlockCipher;
import org.spongycastle.crypto.params.AEADParameters;
import org.spongycastle.crypto.params.KeyParameter;
import org.spongycastle.crypto.params.ParametersWithIV;
/**
* The GMAC specialisation of Galois/Counter mode (GCM) detailed in NIST Special Publication
* 800-38D.
* <p>
* 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).
*/
public class GMac implements Mac
{
private final GCMBlockCipher cipher;
private final int macSizeBits;
/**
* Creates a GMAC based on the operation of a block cipher in GCM mode.
* <p/>
* This will produce an authentication code the length of the block size of the cipher.
*
* @param cipher
* the cipher to be used in GCM mode to generate the MAC.
*/
public GMac(final GCMBlockCipher cipher)
{
// use of this confused flow analyser in some earlier JDKs
this.cipher = cipher;
this.macSizeBits = 128;
}
/**
* Creates a GMAC based on the operation of a 128 bit block cipher in GCM mode.
*
* @param macSizeBits
* the mac size to generate, in bits. Must be a multiple of 8 and >= 96 and <= 128.
* @param cipher
* the cipher to be used in GCM mode to generate the MAC.
*/
public GMac(final GCMBlockCipher cipher, final int macSizeBits)
{
this.cipher = cipher;
this.macSizeBits = macSizeBits;
}
/**
* Initialises the GMAC - requires a {@link ParametersWithIV} providing a {@link KeyParameter}
* and a nonce.
*/
public void init(final CipherParameters params) throws IllegalArgumentException
{
if (params instanceof ParametersWithIV)
{
final ParametersWithIV param = (ParametersWithIV)params;
final byte[] iv = param.getIV();
final KeyParameter keyParam = (KeyParameter)param.getParameters();
// GCM is always operated in encrypt mode to calculate MAC
cipher.init(true, new AEADParameters(keyParam, macSizeBits, iv));
}
else
{
throw new IllegalArgumentException("GMAC requires ParametersWithIV");
}
}
public String getAlgorithmName()
{
return cipher.getUnderlyingCipher().getAlgorithmName() + "-GMAC";
}
public int getMacSize()
{
return macSizeBits / 8;
}
public void update(byte in) throws IllegalStateException
{
cipher.processAADByte(in);
}
public void update(byte[] in, int inOff, int len)
throws DataLengthException, IllegalStateException
{
cipher.processAADBytes(in, inOff, len);
}
public int doFinal(byte[] out, int outOff)
throws DataLengthException, IllegalStateException
{
try
{
return cipher.doFinal(out, outOff);
}
catch (InvalidCipherTextException e)
{
// Impossible in encrypt mode
throw new IllegalStateException(e.toString());
}
}
public void reset()
{
cipher.reset();
}
}
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