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package org.bouncycastle.asn1.x9;
import java.math.BigInteger;
import org.bouncycastle.asn1.ASN1EncodableVector;
import org.bouncycastle.asn1.ASN1Integer;
import org.bouncycastle.asn1.ASN1Object;
import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.ASN1Primitive;
import org.bouncycastle.asn1.ASN1Sequence;
import 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);
}
private X9FieldID(
ASN1Sequence seq)
{
this.id = ASN1ObjectIdentifier.getInstance(seq.getObjectAt(0));
this.parameters = seq.getObjectAt(1).toASN1Primitive();
}
public static X9FieldID getInstance(Object obj)
{
if (obj instanceof X9FieldID)
{
return (X9FieldID)obj;
}
if (obj != null)
{
return new X9FieldID(ASN1Sequence.getInstance(obj));
}
return null;
}
public ASN1ObjectIdentifier getIdentifier()
{
return id;
}
public ASN1Primitive getParameters()
{
return parameters;
}
/**
* Produce a DER encoding of the following structure.
* <pre>
* FieldID ::= SEQUENCE {
* fieldType FIELD-ID.&id({IOSet}),
* parameters FIELD-ID.&Type({IOSet}{@fieldType})
* }
* </pre>
*/
public ASN1Primitive toASN1Primitive()
{
ASN1EncodableVector v = new ASN1EncodableVector();
v.add(this.id);
v.add(this.parameters);
return new DERSequence(v);
}
}
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