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

using System;

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

namespace Org.BouncyCastle.Crypto.Agreement{
  /**
   * a Diffie-Hellman key agreement class.
   * <p>
   * note: This is only the basic algorithm, it doesn't take advantage of
   * long term public keys if they are available. See the DHAgreement class
   * for a "better" implementation.</p>
   */
  public class DHBasicAgreement
    : IBasicAgreement
  {
    private DHPrivateKeyParameters  key;
    private DHParameters      dhParams;

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

      if (!(parameters is DHPrivateKeyParameters))
      {
        throw new ArgumentException("DHEngine expects DHPrivateKeyParameters");
      }

      this.key = (DHPrivateKeyParameters) parameters;
      this.dhParams = key.Parameters;
    }

    /**
     * given a short term public key from a given party calculate the next
     * message in the agreement sequence.
     */
    public BigInteger CalculateAgreement(
      ICipherParameters pubKey)
    {
      if (this.key == null)
        throw new InvalidOperationException("Agreement algorithm not initialised");

      DHPublicKeyParameters pub = (DHPublicKeyParameters)pubKey;

      if (!pub.Parameters.Equals(dhParams))
      {
        throw new ArgumentException("Diffie-Hellman public key has wrong parameters.");
      }

      return pub.Y.ModPow(key.X, dhParams.P);
    }
  }

}