1package org.bouncycastle.crypto.generators;
2
3import java.math.BigInteger;
4import java.security.SecureRandom;
5
6import org.bouncycastle.crypto.params.DHParameters;
7import org.bouncycastle.util.BigIntegers;
8
9class DHKeyGeneratorHelper
10{
11    static final DHKeyGeneratorHelper INSTANCE = new DHKeyGeneratorHelper();
12
13    private static final BigInteger ONE = BigInteger.valueOf(1);
14    private static final BigInteger TWO = BigInteger.valueOf(2);
15
16    private DHKeyGeneratorHelper()
17    {
18    }
19
20    BigInteger calculatePrivate(DHParameters dhParams, SecureRandom random)
21    {
22        BigInteger p = dhParams.getP();
23        int limit = dhParams.getL();
24
25        if (limit != 0)
26        {
27            return new BigInteger(limit, random).setBit(limit - 1);
28        }
29
30        BigInteger min = TWO;
31        int m = dhParams.getM();
32        if (m != 0)
33        {
34            min = ONE.shiftLeft(m - 1);
35        }
36
37        BigInteger max = p.subtract(TWO);
38        BigInteger q = dhParams.getQ();
39        if (q != null)
40        {
41            max = q.subtract(TWO);
42        }
43
44        return BigIntegers.createRandomInRange(min, max, random);
45    }
46
47    BigInteger calculatePublic(DHParameters dhParams, BigInteger x)
48    {
49        return dhParams.getG().modPow(x, dhParams.getP());
50    }
51}
52