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

using System;

using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.X509;
using Org.BouncyCastle.Crypto.Generators;
using Org.BouncyCastle.Crypto.Parameters;

namespace Org.BouncyCastle.Crypto.Agreement.Kdf{
  /**
  * X9.63 based key derivation function for ECDH CMS.
  */
  public class ECDHKekGenerator
    : IDerivationFunction
  {
    private readonly IDerivationFunction kdf;

    private DerObjectIdentifier  algorithm;
    private int          keySize;
    private byte[]        z;

    public ECDHKekGenerator(
      IDigest digest)
    {
      this.kdf = new Kdf2BytesGenerator(digest);
    }

    public void Init(
      IDerivationParameters param)
    {
      DHKdfParameters parameters = (DHKdfParameters)param;

      this.algorithm = parameters.Algorithm;
      this.keySize = parameters.KeySize;
      this.z = parameters.GetZ(); // TODO Clone?
    }

    public IDigest Digest
    {
      get { return kdf.Digest; }
    }

    public int GenerateBytes(
      byte[]  outBytes,
      int    outOff,
      int    len)
    {
      // ECC-CMS-SharedInfo
      DerSequence s = new DerSequence(
        new AlgorithmIdentifier(algorithm, DerNull.Instance),
        new DerTaggedObject(true, 2, new DerOctetString(integerToBytes(keySize))));

      kdf.Init(new KdfParameters(z, s.GetDerEncoded()));

      return kdf.GenerateBytes(outBytes, outOff, len);
    }

    private byte[] integerToBytes(int keySize)
    {
      byte[] val = new byte[4];

      val[0] = (byte)(keySize >> 24);
      val[1] = (byte)(keySize >> 16);
      val[2] = (byte)(keySize >> 8);
      val[3] = (byte)keySize;

      return val;
    }
  }
}