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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 1.6.
package org.bouncycastle.crypto.generators;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.crypto.params.DHParameters;
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)
{
BigInteger p = dhParams.getP();
int limit = dhParams.getL();
if (limit != 0)
{
return new BigInteger(limit, random).setBit(limit - 1);
}
BigInteger min = TWO;
int m = dhParams.getM();
if (m != 0)
{
min = ONE.shiftLeft(m - 1);
}
BigInteger max = p.subtract(TWO);
BigInteger q = dhParams.getQ();
if (q != null)
{
max = q.subtract(TWO);
}
return BigIntegers.createRandomInRange(min, max, random);
}
BigInteger calculatePublic(DHParameters dhParams, BigInteger x)
{
return dhParams.getG().modPow(x, dhParams.getP());
}
}