X9FieldID.cs :  » PDF » iTextSharp » Org » BouncyCastle » Asn1 » X9 » C# / CSharp Open Source

using Org.BouncyCastle.Math;

namespace Org.BouncyCastle.Asn1.X9{
    /**
     * ASN.1 def for Elliptic-Curve Field ID structure. See
     * X9.62, for further details.
     */
    public class X9FieldID
        : Asn1Encodable
    {
        private readonly DerObjectIdentifier  id;
        private readonly Asn1Object parameters;

    /**
     * Constructor for elliptic curves over prime fields
     * <code>F<sub>2</sub></code>.
     * @param primeP The prime <code>p</code> defining the prime field.
     */
    public X9FieldID(
      BigInteger primeP)
    {
      this.id = X9ObjectIdentifiers.PrimeField;
      this.parameters = new DerInteger(primeP);
    }

    /**
     * Constructor for elliptic curves over binary fields
     * <code>F<sub>2<sup>m</sup></sub></code>.
     * @param m  The exponent <code>m</code> of
     * <code>F<sub>2<sup>m</sup></sub></code>.
     * @param k1 The integer <code>k1</code> where <code>x<sup>m</sup> +
     * x<sup>k3</sup> + x<sup>k2</sup> + x<sup>k1</sup> + 1</code>
     * represents the reduction polynomial <code>f(z)</code>.
     * @param k2 The integer <code>k2</code> where <code>x<sup>m</sup> +
     * x<sup>k3</sup> + x<sup>k2</sup> + x<sup>k1</sup> + 1</code>
     * represents the reduction polynomial <code>f(z)</code>.
     * @param k3 The integer <code>k3</code> where <code>x<sup>m</sup> +
     * x<sup>k3</sup> + x<sup>k2</sup> + x<sup>k1</sup> + 1</code>
     * represents the reduction polynomial <code>f(z)</code>..
     */
    public X9FieldID(
      int m,
      int k1,
      int k2,
      int k3)
    {
      this.id = X9ObjectIdentifiers.CharacteristicTwoField;

      Asn1EncodableVector fieldIdParams = new Asn1EncodableVector(new DerInteger(m));

      if (k2 == 0)
      {
        fieldIdParams.Add(
          X9ObjectIdentifiers.TPBasis,
          new DerInteger(k1));
      }
      else
      {
        fieldIdParams.Add(
          X9ObjectIdentifiers.PPBasis,
          new DerSequence(
            new DerInteger(k1),
            new DerInteger(k2),
            new DerInteger(k3)));
      }

      this.parameters = new DerSequence(fieldIdParams);
    }

    internal X9FieldID(
      Asn1Sequence seq)
    {
      this.id = (DerObjectIdentifier) seq[0];
      this.parameters = (Asn1Object) seq[1];
    }

    public DerObjectIdentifier Identifier
        {
            get { return id; }
        }

    public Asn1Object Parameters
        {
            get { return parameters; }
        }

    /**
         * Produce a Der encoding of the following structure.
         * <pre>
         *  FieldID ::= Sequence {
         *      fieldType       FIELD-ID.&amp;id({IOSet}),
         *      parameters      FIELD-ID.&amp;Type({IOSet}{&#64;fieldType})
         *  }
         * </pre>
         */
        public override Asn1Object ToAsn1Object()
        {
      return new DerSequence(id, parameters);
        }
    }
}