ECMqvBasicAgreement.cs :  » PDF » iTextSharp » Org » BouncyCastle » Crypto » Agreement » C# / CSharp Open Source

using System;

using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;

namespace Org.BouncyCastle.Crypto.Agreement{
  public class ECMqvBasicAgreement
    : IBasicAgreement
  {
    protected internal MqvPrivateParameters privParams;

    public void Init(
      ICipherParameters parameters)
    {
      if (parameters is ParametersWithRandom)
      {
        parameters = ((ParametersWithRandom)parameters).Parameters;
      }

      this.privParams = (MqvPrivateParameters)parameters;
    }

    public virtual BigInteger CalculateAgreement(
      ICipherParameters pubKey)
    {
      MqvPublicParameters pubParams = (MqvPublicParameters)pubKey;

      ECPrivateKeyParameters staticPrivateKey = privParams.StaticPrivateKey;

      ECPoint agreement = calculateMqvAgreement(staticPrivateKey.Parameters, staticPrivateKey,
        privParams.EphemeralPrivateKey, privParams.EphemeralPublicKey,
        pubParams.StaticPublicKey, pubParams.EphemeralPublicKey);

      return agreement.X.ToBigInteger();
    }
    
    // The ECMQV Primitive as described in SEC-1, 3.4
    private static ECPoint calculateMqvAgreement(
      ECDomainParameters    parameters,
      ECPrivateKeyParameters  d1U,
      ECPrivateKeyParameters  d2U,
      ECPublicKeyParameters  Q2U,
      ECPublicKeyParameters  Q1V,
      ECPublicKeyParameters  Q2V)
    {
      BigInteger n = parameters.N;
      int e = (n.BitLength + 1) / 2;
      BigInteger powE = BigInteger.One.ShiftLeft(e);

      // The Q2U public key is optional
      ECPoint q;
      if (Q2U == null)
      {
        q = parameters.G.Multiply(d2U.D);
      }
      else
      {
        q = Q2U.Q;
      }

      BigInteger x = q.X.ToBigInteger();
      BigInteger xBar = x.Mod(powE);
      BigInteger Q2UBar = xBar.SetBit(e);
      BigInteger s = d1U.D.Multiply(Q2UBar).Mod(n).Add(d2U.D).Mod(n);

      BigInteger xPrime = Q2V.Q.X.ToBigInteger();
      BigInteger xPrimeBar = xPrime.Mod(powE);
      BigInteger Q2VBar = xPrimeBar.SetBit(e);

      BigInteger hs = parameters.H.Multiply(s).Mod(n);

      //ECPoint p = Q1V.Q.Multiply(Q2VBar).Add(Q2V.Q).Multiply(hs);
      ECPoint p = ECAlgorithms.SumOfTwoMultiplies(
        Q1V.Q, Q2VBar.Multiply(hs).Mod(n), Q2V.Q, hs);

      if (p.IsInfinity)
        throw new InvalidOperationException("Infinity is not a valid agreement value for MQV");

      return p;
    }
  }
}