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

using System;
using System.Globalization;

using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.Nist;
using Org.BouncyCastle.Asn1.Sec;
using Org.BouncyCastle.Asn1.TeleTrust;
using Org.BouncyCastle.Asn1.X9;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;
using Org.BouncyCastle.Security;

namespace Org.BouncyCastle.Crypto.Generators{
    public class ECKeyPairGenerator
    : IAsymmetricCipherKeyPairGenerator
    {
    private readonly string algorithm;

    private ECDomainParameters parameters;
    private DerObjectIdentifier publicKeyParamSet;
        private SecureRandom random;

    public ECKeyPairGenerator()
      : this("EC")
    {
    }

    public ECKeyPairGenerator(
      string algorithm)
    {
      if (algorithm == null)
        throw new ArgumentNullException("algorithm");

      this.algorithm = VerifyAlgorithmName(algorithm);
    }

    public void Init(
            KeyGenerationParameters parameters)
        {
      if (parameters is ECKeyGenerationParameters)
      {
        ECKeyGenerationParameters ecP = (ECKeyGenerationParameters) parameters;

        this.publicKeyParamSet = ecP.PublicKeyParamSet;
        this.parameters = ecP.DomainParameters;
      }
      else
      {
        DerObjectIdentifier oid;
        switch (parameters.Strength)
        {
          case 192:
            oid = X9ObjectIdentifiers.Prime192v1;
            break;
          case 224:
            oid = SecObjectIdentifiers.SecP224r1;
            break;
          case 239:
            oid = X9ObjectIdentifiers.Prime239v1;
            break;
          case 256:
            oid = X9ObjectIdentifiers.Prime256v1;
            break;
          case 384:
            oid = SecObjectIdentifiers.SecP384r1;
            break;
          case 521:
            oid = SecObjectIdentifiers.SecP521r1;
            break;
          default:
            throw new InvalidParameterException("unknown key size.");
        }

        X9ECParameters ecps = FindECCurveByOid(oid);

        this.parameters = new ECDomainParameters(
          ecps.Curve, ecps.G, ecps.N, ecps.H, ecps.GetSeed());
      }

      this.random = parameters.Random;
    }

    /**
         * Given the domain parameters this routine Generates an EC key
         * pair in accordance with X9.62 section 5.2.1 pages 26, 27.
         */
        public AsymmetricCipherKeyPair GenerateKeyPair()
        {
            BigInteger n = parameters.N;
            BigInteger d;

            do
            {
                d = new BigInteger(n.BitLength, random);
            }
            while (d.SignValue == 0 || (d.CompareTo(n) >= 0));

            ECPoint q = parameters.G.Multiply(d);

      if (publicKeyParamSet != null)
      {
        return new AsymmetricCipherKeyPair(
          new ECPublicKeyParameters(algorithm, q, publicKeyParamSet),
          new ECPrivateKeyParameters(algorithm, d, publicKeyParamSet));
      }

      return new AsymmetricCipherKeyPair(
        new ECPublicKeyParameters(algorithm, q, parameters),
        new ECPrivateKeyParameters(algorithm, d, parameters));
    }

    private string VerifyAlgorithmName(
      string algorithm)
    {
      string upper = algorithm.ToUpper(CultureInfo.InvariantCulture);

      switch (upper)
      {
        case "EC":
        case "ECDSA":
        case "ECDH":
        case "ECDHC":
        case "ECGOST3410":
        case "ECMQV":
          break;
        default:
          throw new ArgumentException("unrecognised algorithm: " + algorithm, "algorithm");
      }

      return upper;
    }

    internal static X9ECParameters FindECCurveByOid(DerObjectIdentifier oid)
    {
      // TODO ECGost3410NamedCurves support (returns ECDomainParameters though)

      X9ECParameters ecP = X962NamedCurves.GetByOid(oid);

      if (ecP == null)
      {
        ecP = SecNamedCurves.GetByOid(oid);

        if (ecP == null)
        {
          ecP = NistNamedCurves.GetByOid(oid);

          if (ecP == null)
          {
            ecP = TeleTrusTNamedCurves.GetByOid(oid);
          }
        }
      }

      return ecP;
    }

    internal static ECPublicKeyParameters GetCorrespondingPublicKey(
      ECPrivateKeyParameters privKey)
    {
      ECDomainParameters parameters = privKey.Parameters;
      ECPoint q = parameters.G.Multiply(privKey.D);

      if (privKey.PublicKeyParamSet != null)
      {
        return new ECPublicKeyParameters(privKey.AlgorithmName, q, privKey.PublicKeyParamSet);
      }

      return new ECPublicKeyParameters(privKey.AlgorithmName, q, parameters);
    }
  }
}