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package org.spongycastle.crypto.generators;
import java.math.BigInteger;
import org.spongycastle.crypto.DataLengthException;
import org.spongycastle.crypto.DerivationParameters;
import org.spongycastle.crypto.Mac;
import org.spongycastle.crypto.MacDerivationFunction;
import org.spongycastle.crypto.params.KDFCounterParameters;
import org.spongycastle.crypto.params.KeyParameter;
/**
* This KDF has been defined by the publicly available NIST SP 800-108 specification.
*/
public class KDFCounterBytesGenerator
implements MacDerivationFunction
{
private static final BigInteger INTEGER_MAX = BigInteger.valueOf(Integer.MAX_VALUE);
private static final BigInteger TWO = BigInteger.valueOf(2);
// please refer to the standard for the meaning of the variable names
// all field lengths are in bytes, not in bits as specified by the standard
// fields set by the constructor
private final Mac prf;
private final int h;
// fields set by init
private byte[] fixedInputData;
private int maxSizeExcl;
// ios is i defined as an octet string (the binary representation)
private byte[] ios;
// operational
private int generatedBytes;
// k is used as buffer for all K(i) values
private byte[] k;
public KDFCounterBytesGenerator(Mac prf)
{
this.prf = prf;
this.h = prf.getMacSize();
this.k = new byte[h];
}
public void init(DerivationParameters param)
{
if (!(param instanceof KDFCounterParameters))
{
throw new IllegalArgumentException("Wrong type of arguments given");
}
KDFCounterParameters kdfParams = (KDFCounterParameters)param;
// --- init mac based PRF ---
this.prf.init(new KeyParameter(kdfParams.getKI()));
// --- set arguments ---
this.fixedInputData = kdfParams.getFixedInputData();
int r = kdfParams.getR();
this.ios = new byte[r / 8];
BigInteger maxSize = TWO.pow(r).multiply(BigInteger.valueOf(h));
this.maxSizeExcl = maxSize.compareTo(INTEGER_MAX) == 1 ?
Integer.MAX_VALUE : maxSize.intValue();
// --- set operational state ---
generatedBytes = 0;
}
public Mac getMac()
{
return prf;
}
public int generateBytes(byte[] out, int outOff, int len)
throws DataLengthException, IllegalArgumentException
{
int generatedBytesAfter = generatedBytes + len;
if (generatedBytesAfter < 0 || generatedBytesAfter >= maxSizeExcl)
{
throw new DataLengthException(
"Current KDFCTR may only be used for " + maxSizeExcl + " bytes");
}
if (generatedBytes % h == 0)
{
generateNext();
}
// copy what is left in the currentT (1..hash
int toGenerate = len;
int posInK = generatedBytes % h;
int leftInK = h - generatedBytes % h;
int toCopy = Math.min(leftInK, toGenerate);
System.arraycopy(k, posInK, out, outOff, toCopy);
generatedBytes += toCopy;
toGenerate -= toCopy;
outOff += toCopy;
while (toGenerate > 0)
{
generateNext();
toCopy = Math.min(h, toGenerate);
System.arraycopy(k, 0, out, outOff, toCopy);
generatedBytes += toCopy;
toGenerate -= toCopy;
outOff += toCopy;
}
return len;
}
private void generateNext()
{
int i = generatedBytes / h + 1;
// encode i into counter buffer
switch (ios.length)
{
case 4:
ios[0] = (byte)(i >>> 24);
// fall through
case 3:
ios[ios.length - 3] = (byte)(i >>> 16);
// fall through
case 2:
ios[ios.length - 2] = (byte)(i >>> 8);
// fall through
case 1:
ios[ios.length - 1] = (byte)i;
break;
default:
throw new IllegalStateException("Unsupported size of counter i");
}
// special case for K(0): K(0) is empty, so no update
prf.update(ios, 0, ios.length);
prf.update(fixedInputData, 0, fixedInputData.length);
prf.doFinal(k, 0);
}
}
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