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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
package org.bouncycastle.math.ec.tools;
import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.SortedSet;
import java.util.TreeSet;
import org.bouncycastle.asn1.x9.ECNamedCurveTable;
import org.bouncycastle.asn1.x9.X9ECParameters;
import org.bouncycastle.crypto.ec.CustomNamedCurves;
import org.bouncycastle.math.ec.ECAlgorithms;
import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECFieldElement;
import org.bouncycastle.util.Integers;
public class TraceOptimizer
{
private static final BigInteger ONE = BigInteger.valueOf(1);
private static final SecureRandom R = new SecureRandom();
public static void main(String[] args)
{
SortedSet names = new TreeSet(enumToList(ECNamedCurveTable.getNames()));
names.addAll(enumToList(CustomNamedCurves.getNames()));
Iterator it = names.iterator();
while (it.hasNext())
{
String name = (String)it.next();
X9ECParameters x9 = CustomNamedCurves.getByName(name);
if (x9 == null)
{
x9 = ECNamedCurveTable.getByName(name);
}
if (x9 != null && ECAlgorithms.isF2mCurve(x9.getCurve()))
{
System.out.print(name + ":");
implPrintNonZeroTraceBits(x9);
}
}
}
public static void printNonZeroTraceBits(X9ECParameters x9)
{
if (!ECAlgorithms.isF2mCurve(x9.getCurve()))
{
throw new IllegalArgumentException("Trace only defined over characteristic-2 fields");
}
implPrintNonZeroTraceBits(x9);
}
public static void implPrintNonZeroTraceBits(X9ECParameters x9)
{
ECCurve c = x9.getCurve();
int m = c.getFieldSize();
ArrayList nonZeroTraceBits = new ArrayList();
/*
* Determine which of the bits contribute to the trace.
*
* See section 3.6.2 of "Guide to Elliptic Curve Cryptography" (Hankerson, Menezes, Vanstone)
*/
{
for (int i = 0; i < m; ++i)
{
if (0 == (i & 1) && 0 != i)
{
if (nonZeroTraceBits.contains(Integers.valueOf(i >>> 1)))
{
nonZeroTraceBits.add(Integers.valueOf(i));
System.out.print(" " + i);
}
}
else
{
BigInteger zi = ONE.shiftLeft(i);
ECFieldElement fe = c.fromBigInteger(zi);
int tr = calculateTrace(fe);
if (tr != 0)
{
nonZeroTraceBits.add(Integers.valueOf(i));
System.out.print(" " + i);
}
}
}
System.out.println();
}
/*
* Check calculation based on the non-zero-trace bits against explicit calculation, for random field elements
*/
{
for (int i = 0; i < 1000; ++i)
{
BigInteger x = new BigInteger(m, R);
ECFieldElement fe = c.fromBigInteger(x);
int check = calculateTrace(fe);
int tr = 0;
for (int j = 0; j < nonZeroTraceBits.size(); ++j)
{
int bit = ((Integer)nonZeroTraceBits.get(j)).intValue();
if (x.testBit(bit))
{
tr ^= 1;
}
}
if (check != tr)
{
throw new IllegalStateException("Optimized-trace sanity check failed");
}
}
}
}
private static int calculateTrace(ECFieldElement fe)
{
// int m = fe.getFieldSize();
// ECFieldElement tr = fe;
// for (int i = 1; i < m; ++i)
// {
// tr = tr.square().add(fe);
// }
int m = fe.getFieldSize();
int k = 31 - Integers.numberOfLeadingZeros(m);
int mk = 1;
ECFieldElement tr = fe;
while (k > 0)
{
tr = tr.squarePow(mk).add(tr);
mk = m >>> --k;
if (0 != (mk & 1))
{
tr = tr.square().add(fe);
}
}
if (tr.isZero())
{
return 0;
}
if (tr.isOne())
{
return 1;
}
throw new IllegalStateException("Internal error in trace calculation");
}
private static ArrayList enumToList(Enumeration en)
{
ArrayList rv = new ArrayList();
while (en.hasMoreElements())
{
rv.add(en.nextElement());
}
return rv;
}
}