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147
iTechSharp/srcbc/asn1/x9/X9Curve.cs
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147
iTechSharp/srcbc/asn1/x9/X9Curve.cs
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using System;
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using Org.BouncyCastle.Math;
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using Org.BouncyCastle.Math.EC;
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using Org.BouncyCastle.Utilities;
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namespace Org.BouncyCastle.Asn1.X9
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{
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/**
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* ASN.1 def for Elliptic-Curve Curve structure. See
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* X9.62, for further details.
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*/
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public class X9Curve
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: Asn1Encodable
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{
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private readonly ECCurve curve;
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private readonly byte[] seed;
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private readonly DerObjectIdentifier fieldIdentifier;
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public X9Curve(
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ECCurve curve)
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: this(curve, null)
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{
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this.curve = curve;
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}
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public X9Curve(
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ECCurve curve,
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byte[] seed)
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{
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if (curve == null)
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throw new ArgumentNullException("curve");
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this.curve = curve;
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this.seed = Arrays.Clone(seed);
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if (curve is FpCurve)
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{
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this.fieldIdentifier = X9ObjectIdentifiers.PrimeField;
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}
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else if (curve is F2mCurve)
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{
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this.fieldIdentifier = X9ObjectIdentifiers.CharacteristicTwoField;
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}
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else
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{
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throw new ArgumentException("This type of ECCurve is not implemented");
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}
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}
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public X9Curve(
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X9FieldID fieldID,
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Asn1Sequence seq)
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{
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if (fieldID == null)
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throw new ArgumentNullException("fieldID");
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if (seq == null)
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throw new ArgumentNullException("seq");
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this.fieldIdentifier = fieldID.Identifier;
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if (fieldIdentifier.Equals(X9ObjectIdentifiers.PrimeField))
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{
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BigInteger q = ((DerInteger) fieldID.Parameters).Value;
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X9FieldElement x9A = new X9FieldElement(q, (Asn1OctetString) seq[0]);
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X9FieldElement x9B = new X9FieldElement(q, (Asn1OctetString) seq[1]);
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curve = new FpCurve(q, x9A.Value.ToBigInteger(), x9B.Value.ToBigInteger());
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}
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else
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{
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if (fieldIdentifier.Equals(X9ObjectIdentifiers.CharacteristicTwoField))
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{
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// Characteristic two field
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DerSequence parameters = (DerSequence)fieldID.Parameters;
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int m = ((DerInteger)parameters[0]).Value.IntValue;
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DerObjectIdentifier representation
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= (DerObjectIdentifier)parameters[1];
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int k1 = 0;
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int k2 = 0;
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int k3 = 0;
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if (representation.Equals(X9ObjectIdentifiers.TPBasis))
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{
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// Trinomial basis representation
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k1 = ((DerInteger)parameters[2]).Value.IntValue;
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}
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else
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{
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// Pentanomial basis representation
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DerSequence pentanomial = (DerSequence) parameters[2];
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k1 = ((DerInteger) pentanomial[0]).Value.IntValue;
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k2 = ((DerInteger) pentanomial[1]).Value.IntValue;
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k3 = ((DerInteger) pentanomial[2]).Value.IntValue;
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}
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X9FieldElement x9A = new X9FieldElement(m, k1, k2, k3, (Asn1OctetString)seq[0]);
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X9FieldElement x9B = new X9FieldElement(m, k1, k2, k3, (Asn1OctetString)seq[1]);
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// TODO Is it possible to get the order (n) and cofactor(h) too?
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curve = new F2mCurve(m, k1, k2, k3, x9A.Value.ToBigInteger(), x9B.Value.ToBigInteger());
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}
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}
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if (seq.Count == 3)
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{
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seed = ((DerBitString) seq[2]).GetBytes();
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}
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}
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public ECCurve Curve
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{
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get { return curve; }
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}
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public byte[] GetSeed()
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{
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return Arrays.Clone(seed);
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}
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/**
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* Produce an object suitable for an Asn1OutputStream.
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* <pre>
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* Curve ::= Sequence {
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* a FieldElement,
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* b FieldElement,
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* seed BIT STRING OPTIONAL
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* }
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* </pre>
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*/
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public override Asn1Object ToAsn1Object()
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{
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Asn1EncodableVector v = new Asn1EncodableVector();
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if (fieldIdentifier.Equals(X9ObjectIdentifiers.PrimeField)
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|| fieldIdentifier.Equals(X9ObjectIdentifiers.CharacteristicTwoField))
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{
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v.Add(new X9FieldElement(curve.A).ToAsn1Object());
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v.Add(new X9FieldElement(curve.B).ToAsn1Object());
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}
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if (seed != null)
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{
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v.Add(new DerBitString(seed));
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}
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return new DerSequence(v);
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}
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}
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}
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