content: package local.org.bouncycastle.asn1.x9;
  
  import java.math.BigInteger;
  
  import local.org.bouncycastle.asn1.ASN1EncodableVector;
  import local.org.bouncycastle.asn1.ASN1Integer;
  import local.org.bouncycastle.asn1.ASN1Object;
  import local.org.bouncycastle.asn1.ASN1ObjectIdentifier;
  import local.org.bouncycastle.asn1.ASN1Primitive;
  import local.org.bouncycastle.asn1.ASN1Sequence;
  import local.org.bouncycastle.asn1.DERSequence;
  
  
  /**
   * ASN.1 def for Elliptic-Curve Field ID structure. See
   * X9.62, for further details.
   */
  public class X9FieldID
      extends ASN1Object
      implements X9ObjectIdentifiers
  {
      private ASN1ObjectIdentifier     id;
      private ASN1Primitive 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 = prime_field;
          this.parameters = new ASN1Integer(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 = characteristic_two_field;
          ASN1EncodableVector fieldIdParams = new ASN1EncodableVector();
          fieldIdParams.add(new ASN1Integer(m));
          
          if (k2 == 0) 
          {
              fieldIdParams.add(tpBasis);
              fieldIdParams.add(new ASN1Integer(k1));
          } 
          else 
          {
              fieldIdParams.add(ppBasis);
              ASN1EncodableVector pentanomialParams = new ASN1EncodableVector();
              pentanomialParams.add(new ASN1Integer(k1));
              pentanomialParams.add(new ASN1Integer(k2));
              pentanomialParams.add(new ASN1Integer(k3));
              fieldIdParams.add(new DERSequence(pentanomialParams));
          }
          
          this.parameters = new DERSequence(fieldIdParams);
      }
  
      public X9FieldID(
          ASN1Sequence  seq)
      {
          this.id = (ASN1ObjectIdentifier)seq.getObjectAt(0);
          this.parameters = (ASN1Primitive)seq.getObjectAt(1);
      }
  
      public ASN1ObjectIdentifier getIdentifier()
      {
          return id;
      }
  
      public ASN1Primitive getParameters()
      {
          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 ASN1Primitive toASN1Primitive()
      {
          ASN1EncodableVector v = new ASN1EncodableVector();
  
          v.add(this.id);
          v.add(this.parameters);
  
          return new DERSequence(v);
      }
  }
  