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

using System;
using System.Collections;

using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.Nist;
using Org.BouncyCastle.Asn1.Pkcs;
using Org.BouncyCastle.Asn1.X9;
using Org.BouncyCastle.Crypto.Agreement.Kdf;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security;

namespace Org.BouncyCastle.Crypto.Agreement{
  public class ECDHWithKdfBasicAgreement
    : ECDHBasicAgreement
  {
    private readonly string algorithm;
    private readonly IDerivationFunction kdf;

    public ECDHWithKdfBasicAgreement(
      string        algorithm,
      IDerivationFunction  kdf)
    {
      if (algorithm == null)
        throw new ArgumentNullException("algorithm");
      if (kdf == null)
        throw new ArgumentNullException("kdf");

      this.algorithm = algorithm;
      this.kdf = kdf;
    }

    public override BigInteger CalculateAgreement(
      ICipherParameters pubKey)
    {
      // Note that the ec.KeyAgreement class in JCE only uses kdf in one
      // of the engineGenerateSecret methods.

      BigInteger result = base.CalculateAgreement(pubKey);

      int keySize = GeneratorUtilities.GetDefaultKeySize(algorithm);

      DHKdfParameters dhKdfParams = new DHKdfParameters(
        new DerObjectIdentifier(algorithm),
        keySize,
        bigIntToBytes(result));

      kdf.Init(dhKdfParams);

      byte[] keyBytes = new byte[keySize / 8];
      kdf.GenerateBytes(keyBytes, 0, keyBytes.Length);

      return new BigInteger(1, keyBytes);
    }

    private byte[] bigIntToBytes(
      BigInteger r)
    {
      int byteLength = X9IntegerConverter.GetByteLength(privKey.Parameters.G.X);
      return X9IntegerConverter.IntegerToBytes(r, byteLength);
    }
  }
}