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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 with debug enabled.
package org.bouncycastle.crypto.generators;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.crypto.params.DHParameters;
import org.bouncycastle.math.ec.WNafUtil;
import org.bouncycastle.util.BigIntegers;
class DHKeyGeneratorHelper
{
static final DHKeyGeneratorHelper INSTANCE = new DHKeyGeneratorHelper();
private static final BigInteger ONE = BigInteger.valueOf(1);
private static final BigInteger TWO = BigInteger.valueOf(2);
private DHKeyGeneratorHelper()
{
}
BigInteger calculatePrivate(DHParameters dhParams, SecureRandom random)
{
int limit = dhParams.getL();
if (limit != 0)
{
int minWeight = limit >>> 2;
for (;;)
{
BigInteger x = new BigInteger(limit, random).setBit(limit - 1);
if (WNafUtil.getNafWeight(x) >= minWeight)
{
return x;
}
}
}
BigInteger min = TWO;
int m = dhParams.getM();
if (m != 0)
{
min = ONE.shiftLeft(m - 1);
}
BigInteger q = dhParams.getQ();
if (q == null)
{
q = dhParams.getP();
}
BigInteger max = q.subtract(TWO);
int minWeight = max.bitLength() >>> 2;
for (;;)
{
BigInteger x = BigIntegers.createRandomInRange(min, max, random);
if (WNafUtil.getNafWeight(x) >= minWeight)
{
return x;
}
}
}
BigInteger calculatePublic(DHParameters dhParams, BigInteger x)
{
return dhParams.getG().modPow(x, dhParams.getP());
}
}
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