X9ECParameters.cs :  » PDF » iTextSharp » Org » BouncyCastle » Asn1 » X9 » C# / CSharp Open Source

using System;

using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;

namespace Org.BouncyCastle.Asn1.X9{
    /**
     * ASN.1 def for Elliptic-Curve ECParameters structure. See
     * X9.62, for further details.
     */
    public class X9ECParameters
        : Asn1Encodable
    {
        private X9FieldID  fieldID;
        private ECCurve    curve;
        private ECPoint    g;
        private BigInteger  n;
        private BigInteger  h;
        private byte[]    seed;

    public X9ECParameters(
            Asn1Sequence seq)
        {
            if (!(seq[0] is DerInteger)
               || !((DerInteger) seq[0]).Value.Equals(BigInteger.One))
            {
                throw new ArgumentException("bad version in X9ECParameters");
            }

      X9Curve x9c = null;
            if (seq[2] is X9Curve)
            {
                x9c = (X9Curve) seq[2];
            }
            else
            {
                x9c = new X9Curve(
          new X9FieldID(
            (Asn1Sequence) seq[1]),
            (Asn1Sequence) seq[2]);
            }

      this.curve = x9c.Curve;

      if (seq[3] is X9ECPoint)
            {
                this.g = ((X9ECPoint) seq[3]).Point;
            }
            else
            {
                this.g = new X9ECPoint(curve, (Asn1OctetString) seq[3]).Point;
            }

      this.n = ((DerInteger) seq[4]).Value;
            this.seed = x9c.GetSeed();

      if (seq.Count == 6)
            {
                this.h = ((DerInteger) seq[5]).Value;
            }
        }

    public X9ECParameters(
            ECCurve    curve,
            ECPoint    g,
            BigInteger  n)
            : this(curve, g, n, BigInteger.One, null)
        {
        }

    public X9ECParameters(
            ECCurve    curve,
            ECPoint    g,
            BigInteger  n,
            BigInteger  h)
            : this(curve, g, n, h, null)
        {
        }

    public X9ECParameters(
            ECCurve    curve,
            ECPoint    g,
            BigInteger  n,
            BigInteger  h,
            byte[]    seed)
        {
            this.curve = curve;
            this.g = g;
            this.n = n;
            this.h = h;
            this.seed = seed;

      if (curve is FpCurve)
      {
        this.fieldID = new X9FieldID(((FpCurve) curve).Q);
      }
      else if (curve is F2mCurve)
      {
        F2mCurve curveF2m = (F2mCurve) curve;
        this.fieldID = new X9FieldID(curveF2m.M, curveF2m.K1,
          curveF2m.K2, curveF2m.K3);
      }
        }

    public ECCurve Curve
        {
      get { return curve; }
        }

    public ECPoint G
        {
            get { return g; }
        }

    public BigInteger N
        {
            get { return n; }
        }

    public BigInteger H
        {
            get
      {
        if (h == null)
        {
          // TODO - this should be calculated, it will cause issues with custom curves.
          return BigInteger.One;
        }

        return h;
      }
        }

    public byte[] GetSeed()
        {
            return seed;
        }

    /**
         * Produce an object suitable for an Asn1OutputStream.
         * <pre>
         *  ECParameters ::= Sequence {
         *      version         Integer { ecpVer1(1) } (ecpVer1),
         *      fieldID         FieldID {{FieldTypes}},
         *      curve           X9Curve,
         *      base            X9ECPoint,
         *      order           Integer,
         *      cofactor        Integer OPTIONAL
         *  }
         * </pre>
         */
        public override Asn1Object ToAsn1Object()
        {
            Asn1EncodableVector v = new Asn1EncodableVector(
        new DerInteger(1),
        fieldID,
        new X9Curve(curve, seed),
        new X9ECPoint(g),
        new DerInteger(n));

      if (h != null)
            {
                v.Add(new DerInteger(h));
            }

      return new DerSequence(v);
        }
    }
}