DHKeyGeneratorHelper.cs :  » PDF » iTextSharp » Org » BouncyCastle » Crypto » Generators » C# / CSharp Open Source

using System;

using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Utilities;

namespace Org.BouncyCastle.Crypto.Generators{
  class DHKeyGeneratorHelper
  {
    internal static readonly DHKeyGeneratorHelper Instance = new DHKeyGeneratorHelper();

    private DHKeyGeneratorHelper()
    {
    }

    internal BigInteger CalculatePrivate(
      DHParameters  dhParams,
      SecureRandom  random)
    {
      int limit = dhParams.L;

      if (limit != 0)
      {
        return new BigInteger(limit, random).SetBit(limit - 1);
      }

      BigInteger min = BigInteger.Two;
      int m = dhParams.M;
      if (m != 0)
      {
        min = BigInteger.One.ShiftLeft(m - 1);
      }

      BigInteger max = dhParams.P.Subtract(BigInteger.Two);
      BigInteger q = dhParams.Q;
      if (q != null)
      {
        max = q.Subtract(BigInteger.Two);
      }

      return BigIntegers.CreateRandomInRange(min, max, random);
    }

    internal BigInteger CalculatePublic(
      DHParameters  dhParams,
      BigInteger    x)
    {
      return dhParams.G.ModPow(x, dhParams.P);
    }
  }
}