public X9Curve(
X9FieldID fieldID,
Asn1Sequence seq)
{
if(fieldID == null)
throw new ArgumentNullException("fieldID");
if(seq == null)
throw new ArgumentNullException("seq");
this.fieldIdentifier = fieldID.Identifier;
if(fieldIdentifier.Equals(X9ObjectIdentifiers.PrimeField))
{
BigInteger q = ((DerInteger)fieldID.Parameters).Value;
X9FieldElement x9A = new X9FieldElement(q, (Asn1OctetString)seq[0]);
X9FieldElement x9B = new X9FieldElement(q, (Asn1OctetString)seq[1]);
curve = new FpCurve(q, x9A.Value.ToBigInteger(), x9B.Value.ToBigInteger());
}
else
{
if(fieldIdentifier.Equals(X9ObjectIdentifiers.CharacteristicTwoField))
{
// Characteristic two field
DerSequence parameters = (DerSequence)fieldID.Parameters;
int m = ((DerInteger)parameters[0]).Value.IntValue;
DerObjectIdentifier representation
= (DerObjectIdentifier)parameters[1];
int k1 = 0;
int k2 = 0;
int k3 = 0;
if(representation.Equals(X9ObjectIdentifiers.TPBasis))
{
// Trinomial basis representation
k1 = ((DerInteger)parameters[2]).Value.IntValue;
}
else
{
// Pentanomial basis representation
DerSequence pentanomial = (DerSequence)parameters[2];
k1 = ((DerInteger)pentanomial[0]).Value.IntValue;
k2 = ((DerInteger)pentanomial[1]).Value.IntValue;
k3 = ((DerInteger)pentanomial[2]).Value.IntValue;
}
X9FieldElement x9A = new X9FieldElement(m, k1, k2, k3, (Asn1OctetString)seq[0]);
X9FieldElement x9B = new X9FieldElement(m, k1, k2, k3, (Asn1OctetString)seq[1]);
// TODO Is it possible to get the order (n) and cofactor(h) too?
curve = new F2mCurve(m, k1, k2, k3, x9A.Value.ToBigInteger(), x9B.Value.ToBigInteger());
}
}
}
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");
}
}
