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using System;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;
using Org.BouncyCastle.Math.Field;
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 X9ECPoint g;
private BigInteger n;
private BigInteger h;
private byte[] seed;
public static X9ECParameters GetInstance(object obj)
{
if (obj is X9ECParameters)
return (X9ECParameters)obj;
if (obj != null)
return new X9ECParameters(Asn1Sequence.GetInstance(obj));
return null;
}
public X9ECParameters(
Asn1Sequence seq)
{
if (!(seq[0] is DerInteger)
|| !((DerInteger)seq[0]).HasValue(1))
{
throw new ArgumentException("bad version in X9ECParameters");
}
this.n = ((DerInteger)seq[4]).Value;
if (seq.Count == 6)
{
this.h = ((DerInteger)seq[5]).Value;
}
X9Curve x9c = new X9Curve(
X9FieldID.GetInstance(seq[1]), n, h,
Asn1Sequence.GetInstance(seq[2]));
this.curve = x9c.Curve;
object p = seq[3];
if (p is X9ECPoint)
{
this.g = (X9ECPoint)p;
}
else
{
this.g = new X9ECPoint(curve, (Asn1OctetString)p);
}
this.seed = x9c.GetSeed();
}
public X9ECParameters(
ECCurve curve,
X9ECPoint g,
BigInteger n)
: this(curve, g, n, null, null)
{
}
public X9ECParameters(
ECCurve curve,
X9ECPoint g,
BigInteger n,
BigInteger h)
: this(curve, g, n, h, null)
{
}
public X9ECParameters(
ECCurve curve,
X9ECPoint g,
BigInteger n,
BigInteger h,
byte[] seed)
{
this.curve = curve;
this.g = g;
this.n = n;
this.h = h;
this.seed = seed;
if (ECAlgorithms.IsFpCurve(curve))
{
this.fieldID = new X9FieldID(curve.Field.Characteristic);
}
else if (ECAlgorithms.IsF2mCurve(curve))
{
IPolynomialExtensionField field = (IPolynomialExtensionField)curve.Field;
int[] exponents = field.MinimalPolynomial.GetExponentsPresent();
if (exponents.Length == 3)
{
this.fieldID = new X9FieldID(exponents[2], exponents[1]);
}
else if (exponents.Length == 5)
{
this.fieldID = new X9FieldID(exponents[4], exponents[1], exponents[2], exponents[3]);
}
else
{
throw new ArgumentException("Only trinomial and pentomial curves are supported");
}
}
else
{
throw new ArgumentException("'curve' is of an unsupported type");
}
}
public ECCurve Curve
{
get { return curve; }
}
public ECPoint G
{
get { return g.Point; }
}
public BigInteger N
{
get { return n; }
}
public BigInteger H
{
get { return h; }
}
public byte[] GetSeed()
{
return seed;
}
/**
* Return the ASN.1 entry representing the Curve.
*
* @return the X9Curve for the curve in these parameters.
*/
public X9Curve CurveEntry
{
get { return new X9Curve(curve, seed); }
}
/**
* Return the ASN.1 entry representing the FieldID.
*
* @return the X9FieldID for the FieldID in these parameters.
*/
public X9FieldID FieldIDEntry
{
get { return fieldID; }
}
/**
* Return the ASN.1 entry representing the base point G.
*
* @return the X9ECPoint for the base point in these parameters.
*/
public X9ECPoint BaseEntry
{
get { return g; }
}
/**
* 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(BigInteger.One),
fieldID,
new X9Curve(curve, seed),
g,
new DerInteger(n));
if (h != null)
{
v.Add(new DerInteger(h));
}
return new DerSequence(v);
}
}
}
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