org.bouncycastle.crypto.modes.gcm.Tables1kGCMExponentiator Maven / Gradle / Ivy
package org.bouncycastle.crypto.modes.gcm;
import java.util.Vector;
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)
{
long[] y = GCMUtil.asLongs(x);
if (lookupPowX2 != null && 0L != GCMUtil.areEqual(y, (long[])lookupPowX2.elementAt(0)))
{
return;
}
lookupPowX2 = new Vector(8);
lookupPowX2.addElement(y);
}
public void exponentiateX(long pow, byte[] output)
{
long[] y = GCMUtil.oneAsLongs();
int bit = 0;
while (pow > 0)
{
if ((pow & 1L) != 0)
{
ensureAvailable(bit);
GCMUtil.multiply(y, (long[])lookupPowX2.elementAt(bit));
}
++bit;
pow >>>= 1;
}
GCMUtil.asBytes(y, output);
}
private void ensureAvailable(int bit)
{
int last = lookupPowX2.size() - 1;
if (last < bit)
{
long[] prev = (long[])lookupPowX2.elementAt(last);
do
{
long[] next = new long[GCMUtil.SIZE_LONGS];
GCMUtil.square(prev, next);
lookupPowX2.addElement(next);
prev = next;
}
while (++last < bit);
}
}
}