com.bugvm.bouncycastle.crypto.modes.gcm.Tables1kGCMExponentiator Maven / Gradle / Ivy
package com.bugvm.bouncycastle.crypto.modes.gcm;
import java.util.Vector;
import com.bugvm.bouncycastle.util.Arrays;
public class Tables1kGCMExponentiator implements GCMExponentiator
{
// A lookup table of the power-of-two powers of 'x'
// - lookupPowX2[i] = x^(2^i)
private Vector lookupPowX2;
public void init(byte[] x)
{
if (lookupPowX2 != null && Arrays.areEqual(x, (byte[])lookupPowX2.elementAt(0)))
{
return;
}
lookupPowX2 = new Vector(8);
lookupPowX2.addElement(Arrays.clone(x));
}
public void exponentiateX(long pow, byte[] output)
{
byte[] y = GCMUtil.oneAsBytes();
int bit = 0;
while (pow > 0)
{
if ((pow & 1L) != 0)
{
ensureAvailable(bit);
GCMUtil.multiply(y, (byte[])lookupPowX2.elementAt(bit));
}
++bit;
pow >>>= 1;
}
System.arraycopy(y, 0, output, 0, 16);
}
private void ensureAvailable(int bit)
{
int count = lookupPowX2.size();
if (count <= bit)
{
byte[] tmp = (byte[])lookupPowX2.elementAt(count - 1);
do
{
tmp = Arrays.clone(tmp);
GCMUtil.multiply(tmp, tmp);
lookupPowX2.addElement(tmp);
}
while (++count <= bit);
}
}
}