public ECDomainParameters(
ECCurve curve,
ECPoint g,
BigInteger n)
: this(curve, g, n, BigInteger.One)
{
}
public X9ECParameters(
ECCurve curve,
ECPoint g,
BigInteger n)
: this(curve, g, n, BigInteger.One, null)
{
}
public static ECPoint ImportPoint(ECCurve c, ECPoint p)
{
ECCurve cp = p.Curve;
if (!c.Equals(cp))
throw new ArgumentException("Point must be on the same curve");
return c.ImportPoint(p);
}
public ECDomainParameters(
ECCurve curve,
ECPoint g,
BigInteger n,
BigInteger h)
: this(curve, g, n, h, null)
{
}
public ECPublicKeyParameters(
ECPoint q,
DerObjectIdentifier publicKeyParamSet)
: base("ECGOST3410", false, publicKeyParamSet)
{
if (q == null)
throw new ArgumentNullException("q");
this.q = q.Normalize();
}
public ECPublicKeyParameters(
string algorithm,
ECPoint q,
DerObjectIdentifier publicKeyParamSet)
: base(algorithm, false, publicKeyParamSet)
{
if (q == null)
throw new ArgumentNullException("q");
this.q = q.Normalize();
}
public ECPublicKeyParameters(
string algorithm,
ECPoint q,
ECDomainParameters parameters)
: base(algorithm, false, parameters)
{
if (q == null)
throw new ArgumentNullException("q");
this.q = q.Normalize();
}
public X9ECParameters(
Asn1Sequence seq)
{
if (!(seq[0] is DerInteger)
|| !((DerInteger) seq[0]).Value.Equals(BigInteger.One))
{
throw new ArgumentException("bad version in X9ECParameters");
}
X9Curve x9c = null;
if (seq[2] is X9Curve)
{
x9c = (X9Curve) seq[2];
}
else
{
x9c = new X9Curve(
new X9FieldID(
(Asn1Sequence) seq[1]),
(Asn1Sequence) seq[2]);
}
this.curve = x9c.Curve;
if (seq[3] is X9ECPoint)
{
this.g = ((X9ECPoint) seq[3]).Point;
}
else
{
this.g = new X9ECPoint(curve, (Asn1OctetString) seq[3]).Point;
}
this.n = ((DerInteger) seq[4]).Value;
this.seed = x9c.GetSeed();
if (seq.Count == 6)
{
this.h = ((DerInteger) seq[5]).Value;
}
}
public ECDomainParameters(
ECCurve curve,
ECPoint g,
BigInteger n,
BigInteger h,
byte[] seed)
{
if (curve == null)
throw new ArgumentNullException("curve");
if (g == null)
throw new ArgumentNullException("g");
if (n == null)
throw new ArgumentNullException("n");
if (h == null)
throw new ArgumentNullException("h");
this.curve = curve;
this.g = g.Normalize();
this.n = n;
this.h = h;
this.seed = Arrays.Clone(seed);
}
/**
* Simple shift-and-add multiplication. Serves as reference implementation
* to verify (possibly faster) implementations, and for very small scalars.
*
* @param p
* The point to multiply.
* @param k
* The multiplier.
* @return The result of the point multiplication <code>kP</code>.
*/
public static ECPoint ReferenceMultiply(ECPoint p, BigInteger k)
{
BigInteger x = k.Abs();
ECPoint q = p.Curve.Infinity;
int t = x.BitLength;
if (t > 0)
{
if (x.TestBit(0))
{
q = p;
}
for (int i = 1; i < t; i++)
{
p = p.Twice();
if (x.TestBit(i))
{
q = q.Add(p);
}
}
}
return k.SignValue < 0 ? q.Negate() : q;
}
// The ECMQV Primitive as described in SEC-1, 3.4
private static ECPoint CalculateMqvAgreement(
ECDomainParameters parameters,
ECPrivateKeyParameters d1U,
ECPrivateKeyParameters d2U,
ECPublicKeyParameters Q2U,
ECPublicKeyParameters Q1V,
ECPublicKeyParameters Q2V)
{
BigInteger n = parameters.N;
int e = (n.BitLength + 1) / 2;
BigInteger powE = BigInteger.One.ShiftLeft(e);
ECCurve curve = parameters.Curve;
ECPoint[] points = new ECPoint[]{
// The Q2U public key is optional
ECAlgorithms.ImportPoint(curve, Q2U == null ? parameters.G.Multiply(d2U.D) : Q2U.Q),
ECAlgorithms.ImportPoint(curve, Q1V.Q),
ECAlgorithms.ImportPoint(curve, Q2V.Q)
};
curve.NormalizeAll(points);
ECPoint q2u = points[0], q1v = points[1], q2v = points[2];
BigInteger x = q2u.AffineXCoord.ToBigInteger();
BigInteger xBar = x.Mod(powE);
BigInteger Q2UBar = xBar.SetBit(e);
BigInteger s = d1U.D.Multiply(Q2UBar).Add(d2U.D).Mod(n);
BigInteger xPrime = q2v.AffineXCoord.ToBigInteger();
BigInteger xPrimeBar = xPrime.Mod(powE);
BigInteger Q2VBar = xPrimeBar.SetBit(e);
BigInteger hs = parameters.H.Multiply(s).Mod(n);
return ECAlgorithms.SumOfTwoMultiplies(
q1v, Q2VBar.Multiply(hs).Mod(n), q2v, hs);
}
internal static ECPoint ImplSumOfMultiplies(ECPoint[] ps, BigInteger[] ks)
{
int count = ps.Length;
bool[] negs = new bool[count];
WNafPreCompInfo[] infos = new WNafPreCompInfo[count];
byte[][] wnafs = new byte[count][];
for (int i = 0; i < count; ++i)
{
BigInteger ki = ks[i]; negs[i] = ki.SignValue < 0; ki = ki.Abs();
int width = System.Math.Max(2, System.Math.Min(16, WNafUtilities.GetWindowSize(ki.BitLength)));
infos[i] = WNafUtilities.Precompute(ps[i], width, true);
wnafs[i] = WNafUtilities.GenerateWindowNaf(width, ki);
}
return ImplSumOfMultiplies(negs, infos, wnafs);
}
internal static ECPoint ImplShamirsTrickWNaf(ECPoint P, BigInteger k, ECPointMap pointMapQ, BigInteger l)
{
bool negK = k.SignValue < 0, negL = l.SignValue < 0;
k = k.Abs();
l = l.Abs();
int width = System.Math.Max(2, System.Math.Min(16, WNafUtilities.GetWindowSize(System.Math.Max(k.BitLength, l.BitLength))));
ECPoint Q = WNafUtilities.MapPointWithPrecomp(P, width, true, pointMapQ);
WNafPreCompInfo infoP = WNafUtilities.GetWNafPreCompInfo(P);
WNafPreCompInfo infoQ = WNafUtilities.GetWNafPreCompInfo(Q);
ECPoint[] preCompP = negK ? infoP.PreCompNeg : infoP.PreComp;
ECPoint[] preCompQ = negL ? infoQ.PreCompNeg : infoQ.PreComp;
ECPoint[] preCompNegP = negK ? infoP.PreComp : infoP.PreCompNeg;
ECPoint[] preCompNegQ = negL ? infoQ.PreComp : infoQ.PreCompNeg;
byte[] wnafP = WNafUtilities.GenerateWindowNaf(width, k);
byte[] wnafQ = WNafUtilities.GenerateWindowNaf(width, l);
return ImplShamirsTrickWNaf(preCompP, preCompNegP, wnafP, preCompQ, preCompNegQ, wnafQ);
}
internal static ECPoint ImplShamirsTrickJsf(ECPoint P, BigInteger k, ECPoint Q, BigInteger l)
{
ECCurve curve = P.Curve;
ECPoint infinity = curve.Infinity;
// TODO conjugate co-Z addition (ZADDC) can return both of these
ECPoint PaddQ = P.Add(Q);
ECPoint PsubQ = P.Subtract(Q);
ECPoint[] points = new ECPoint[] { Q, PsubQ, P, PaddQ };
curve.NormalizeAll(points);
ECPoint[] table = new ECPoint[] {
points[3].Negate(), points[2].Negate(), points[1].Negate(),
points[0].Negate(), infinity, points[0],
points[1], points[2], points[3] };
byte[] jsf = WNafUtilities.GenerateJsf(k, l);
ECPoint R = infinity;
int i = jsf.Length;
while (--i >= 0)
{
int jsfi = jsf[i];
// NOTE: The shifting ensures the sign is extended correctly
int kDigit = ((jsfi << 24) >> 28), lDigit = ((jsfi << 28) >> 28);
int index = 4 + (kDigit * 3) + lDigit;
R = R.TwicePlus(table[index]);
}
return R;
}
public static ECPoint ValidatePoint(ECPoint p)
{
if (!p.IsValid())
throw new ArgumentException("Invalid point", "p");
return p;
}
public static ECPoint SumOfTwoMultiplies(ECPoint P, BigInteger a, ECPoint Q, BigInteger b)
{
ECCurve cp = P.Curve;
Q = ImportPoint(cp, Q);
// Point multiplication for Koblitz curves (using WTNAF) beats Shamir's trick
if (cp is F2mCurve)
{
F2mCurve f2mCurve = (F2mCurve) cp;
if (f2mCurve.IsKoblitz)
{
return ValidatePoint(P.Multiply(a).Add(Q.Multiply(b)));
}
}
GlvEndomorphism glvEndomorphism = cp.GetEndomorphism() as GlvEndomorphism;
if (glvEndomorphism != null)
{
return ValidatePoint(
ImplSumOfMultipliesGlv(new ECPoint[] { P, Q }, new BigInteger[] { a, b }, glvEndomorphism));
}
return ValidatePoint(ImplShamirsTrickWNaf(P, a, Q, b));
}
public abstract ECPoint Add(ECPoint b);
private static ECPoint ImplShamirsTrickWNaf(ECPoint[] preCompP, ECPoint[] preCompNegP, byte[] wnafP,
ECPoint[] preCompQ, ECPoint[] preCompNegQ, byte[] wnafQ)
{
int len = System.Math.Max(wnafP.Length, wnafQ.Length);
ECCurve curve = preCompP[0].Curve;
ECPoint infinity = curve.Infinity;
ECPoint R = infinity;
int zeroes = 0;
for (int i = len - 1; i >= 0; --i)
{
int wiP = i < wnafP.Length ? (int)(sbyte)wnafP[i] : 0;
int wiQ = i < wnafQ.Length ? (int)(sbyte)wnafQ[i] : 0;
if ((wiP | wiQ) == 0)
{
++zeroes;
continue;
}
ECPoint r = infinity;
if (wiP != 0)
{
int nP = System.Math.Abs(wiP);
ECPoint[] tableP = wiP < 0 ? preCompNegP : preCompP;
r = r.Add(tableP[nP >> 1]);
}
if (wiQ != 0)
{
int nQ = System.Math.Abs(wiQ);
ECPoint[] tableQ = wiQ < 0 ? preCompNegQ : preCompQ;
r = r.Add(tableQ[nQ >> 1]);
}
if (zeroes > 0)
{
R = R.TimesPow2(zeroes);
zeroes = 0;
}
R = R.TwicePlus(r);
}
if (zeroes > 0)
{
R = R.TimesPow2(zeroes);
}
return R;
}
/*
* "Shamir's Trick", originally due to E. G. Straus
* (Addition chains of vectors. American Mathematical Monthly,
* 71(7):806-808, Aug./Sept. 1964)
*
* Input: The points P, Q, scalar k = (km?, ... , k1, k0)
* and scalar l = (lm?, ... , l1, l0).
* Output: R = k * P + l * Q.
* 1: Z <- P + Q
* 2: R <- O
* 3: for i from m-1 down to 0 do
* 4: R <- R + R {point doubling}
* 5: if (ki = 1) and (li = 0) then R <- R + P end if
* 6: if (ki = 0) and (li = 1) then R <- R + Q end if
* 7: if (ki = 1) and (li = 1) then R <- R + Z end if
* 8: end for
* 9: return R
*/
public static ECPoint ShamirsTrick(ECPoint P, BigInteger k, ECPoint Q, BigInteger l)
{
ECCurve cp = P.Curve;
Q = ImportPoint(cp, Q);
return ValidatePoint(ImplShamirsTrickJsf(P, k, Q, l));
}
// B.3 pg 62
public override ECPoint Add(ECPoint b)
{
if (this.IsInfinity)
return b;
if (b.IsInfinity)
return this;
if (this == b)
return Twice();
ECCurve curve = this.Curve;
int coord = curve.CoordinateSystem;
ECFieldElement X1 = this.RawXCoord, Y1 = this.RawYCoord;
ECFieldElement X2 = b.RawXCoord, Y2 = b.RawYCoord;
switch (coord)
{
case ECCurve.COORD_AFFINE:
{
ECFieldElement dx = X2.Subtract(X1), dy = Y2.Subtract(Y1);
if (dx.IsZero)
{
if (dy.IsZero)
{
// this == b, i.e. this must be doubled
return Twice();
}
// this == -b, i.e. the result is the point at infinity
return Curve.Infinity;
}
ECFieldElement gamma = dy.Divide(dx);
ECFieldElement X3 = gamma.Square().Subtract(X1).Subtract(X2);
ECFieldElement Y3 = gamma.Multiply(X1.Subtract(X3)).Subtract(Y1);
return new FpPoint(Curve, X3, Y3, IsCompressed);
}
case ECCurve.COORD_HOMOGENEOUS:
{
ECFieldElement Z1 = this.RawZCoords[0];
ECFieldElement Z2 = b.RawZCoords[0];
bool Z1IsOne = Z1.IsOne;
bool Z2IsOne = Z2.IsOne;
ECFieldElement u1 = Z1IsOne ? Y2 : Y2.Multiply(Z1);
ECFieldElement u2 = Z2IsOne ? Y1 : Y1.Multiply(Z2);
ECFieldElement u = u1.Subtract(u2);
ECFieldElement v1 = Z1IsOne ? X2 : X2.Multiply(Z1);
ECFieldElement v2 = Z2IsOne ? X1 : X1.Multiply(Z2);
ECFieldElement v = v1.Subtract(v2);
// Check if b == this or b == -this
if (v.IsZero)
{
if (u.IsZero)
{
// this == b, i.e. this must be doubled
return this.Twice();
}
// this == -b, i.e. the result is the point at infinity
return curve.Infinity;
}
// TODO Optimize for when w == 1
ECFieldElement w = Z1IsOne ? Z2 : Z2IsOne ? Z1 : Z1.Multiply(Z2);
ECFieldElement vSquared = v.Square();
ECFieldElement vCubed = vSquared.Multiply(v);
ECFieldElement vSquaredV2 = vSquared.Multiply(v2);
ECFieldElement A = u.Square().Multiply(w).Subtract(vCubed).Subtract(Two(vSquaredV2));
ECFieldElement X3 = v.Multiply(A);
ECFieldElement Y3 = vSquaredV2.Subtract(A).MultiplyMinusProduct(u, u2, vCubed);
ECFieldElement Z3 = vCubed.Multiply(w);
return new FpPoint(curve, X3, Y3, new ECFieldElement[] { Z3 }, IsCompressed);
}
case ECCurve.COORD_JACOBIAN:
case ECCurve.COORD_JACOBIAN_MODIFIED:
{
ECFieldElement Z1 = this.RawZCoords[0];
ECFieldElement Z2 = b.RawZCoords[0];
bool Z1IsOne = Z1.IsOne;
ECFieldElement X3, Y3, Z3, Z3Squared = null;
if (!Z1IsOne && Z1.Equals(Z2))
{
// TODO Make this available as public method coZAdd?
ECFieldElement dx = X1.Subtract(X2), dy = Y1.Subtract(Y2);
if (dx.IsZero)
{
if (dy.IsZero)
{
return Twice();
}
return curve.Infinity;
}
ECFieldElement C = dx.Square();
ECFieldElement W1 = X1.Multiply(C), W2 = X2.Multiply(C);
ECFieldElement A1 = W1.Subtract(W2).Multiply(Y1);
X3 = dy.Square().Subtract(W1).Subtract(W2);
Y3 = W1.Subtract(X3).Multiply(dy).Subtract(A1);
Z3 = dx;
if (Z1IsOne)
{
Z3Squared = C;
}
else
{
Z3 = Z3.Multiply(Z1);
}
}
else
{
ECFieldElement Z1Squared, U2, S2;
if (Z1IsOne)
{
Z1Squared = Z1; U2 = X2; S2 = Y2;
}
else
{
Z1Squared = Z1.Square();
U2 = Z1Squared.Multiply(X2);
ECFieldElement Z1Cubed = Z1Squared.Multiply(Z1);
S2 = Z1Cubed.Multiply(Y2);
}
bool Z2IsOne = Z2.IsOne;
ECFieldElement Z2Squared, U1, S1;
if (Z2IsOne)
{
Z2Squared = Z2; U1 = X1; S1 = Y1;
}
else
{
Z2Squared = Z2.Square();
U1 = Z2Squared.Multiply(X1);
ECFieldElement Z2Cubed = Z2Squared.Multiply(Z2);
S1 = Z2Cubed.Multiply(Y1);
}
ECFieldElement H = U1.Subtract(U2);
ECFieldElement R = S1.Subtract(S2);
// Check if b == this or b == -this
if (H.IsZero)
{
if (R.IsZero)
{
// this == b, i.e. this must be doubled
return this.Twice();
}
// this == -b, i.e. the result is the point at infinity
return curve.Infinity;
}
ECFieldElement HSquared = H.Square();
ECFieldElement G = HSquared.Multiply(H);
ECFieldElement V = HSquared.Multiply(U1);
X3 = R.Square().Add(G).Subtract(Two(V));
Y3 = V.Subtract(X3).MultiplyMinusProduct(R, G, S1);
Z3 = H;
if (!Z1IsOne)
{
Z3 = Z3.Multiply(Z1);
}
if (!Z2IsOne)
{
Z3 = Z3.Multiply(Z2);
}
// Alternative calculation of Z3 using fast square
//X3 = four(X3);
//Y3 = eight(Y3);
//Z3 = doubleProductFromSquares(Z1, Z2, Z1Squared, Z2Squared).Multiply(H);
if (Z3 == H)
{
Z3Squared = HSquared;
}
}
ECFieldElement[] zs;
if (coord == ECCurve.COORD_JACOBIAN_MODIFIED)
{
// TODO If the result will only be used in a subsequent addition, we don't need W3
ECFieldElement W3 = CalculateJacobianModifiedW(Z3, Z3Squared);
zs = new ECFieldElement[] { Z3, W3 };
}
else
{
zs = new ECFieldElement[] { Z3 };
}
return new FpPoint(curve, X3, Y3, zs, IsCompressed);
}
default:
{
throw new InvalidOperationException("unsupported coordinate system");
}
}
}
/* (non-Javadoc)
* @see BitcoinKit.BouncyCastle.math.ec.ECPoint#subtract(BitcoinKit.BouncyCastle.math.ec.ECPoint)
*/
public override ECPoint Subtract(
ECPoint b)
{
CheckPoints(this, b);
return SubtractSimple((F2mPoint) b);
}
public virtual ECPoint TwicePlus(ECPoint b)
{
return Twice().Add(b);
}
public abstract ECPoint Subtract(ECPoint b);
public virtual bool Equals(ECPoint other)
{
if (this == other)
return true;
if (null == other)
return false;
ECCurve c1 = this.Curve, c2 = other.Curve;
bool n1 = (null == c1), n2 = (null == c2);
bool i1 = IsInfinity, i2 = other.IsInfinity;
if (i1 || i2)
{
return (i1 && i2) && (n1 || n2 || c1.Equals(c2));
}
ECPoint p1 = this, p2 = other;
if (n1 && n2)
{
// Points with null curve are in affine form, so already normalized
}
else if (n1)
{
p2 = p2.Normalize();
}
else if (n2)
{
p1 = p1.Normalize();
}
else if (!c1.Equals(c2))
{
return false;
}
else
{
// TODO Consider just requiring already normalized, to avoid silent performance degradation
ECPoint[] points = new ECPoint[] { this, c1.ImportPoint(p2) };
// TODO This is a little strong, really only requires coZNormalizeAll to get Zs equal
c1.NormalizeAll(points);
p1 = points[0];
p2 = points[1];
}
return p1.XCoord.Equals(p2.XCoord) && p1.YCoord.Equals(p2.YCoord);
}
internal static ECPoint ImplSumOfMultiplies(ECPoint[] ps, ECPointMap pointMap, BigInteger[] ks)
{
int halfCount = ps.Length, fullCount = halfCount << 1;
bool[] negs = new bool[fullCount];
WNafPreCompInfo[] infos = new WNafPreCompInfo[fullCount];
byte[][] wnafs = new byte[fullCount][];
for (int i = 0; i < halfCount; ++i)
{
int j0 = i << 1, j1 = j0 + 1;
BigInteger kj0 = ks[j0]; negs[j0] = kj0.SignValue < 0; kj0 = kj0.Abs();
BigInteger kj1 = ks[j1]; negs[j1] = kj1.SignValue < 0; kj1 = kj1.Abs();
int width = System.Math.Max(2, System.Math.Min(16, WNafUtilities.GetWindowSize(System.Math.Max(kj0.BitLength, kj1.BitLength))));
ECPoint P = ps[i], Q = WNafUtilities.MapPointWithPrecomp(P, width, true, pointMap);
infos[j0] = WNafUtilities.GetWNafPreCompInfo(P);
infos[j1] = WNafUtilities.GetWNafPreCompInfo(Q);
wnafs[j0] = WNafUtilities.GenerateWindowNaf(width, kj0);
wnafs[j1] = WNafUtilities.GenerateWindowNaf(width, kj1);
}
return ImplSumOfMultiplies(negs, infos, wnafs);
}
/**
* Check, if two <code>ECPoint</code>s can be added or subtracted.
* @param a The first <code>ECPoint</code> to check.
* @param b The second <code>ECPoint</code> to check.
* @throws IllegalArgumentException if <code>a</code> and <code>b</code>
* cannot be added.
*/
private static void CheckPoints(
ECPoint a,
ECPoint b)
{
// Check, if points are on the same curve
if (!a.Curve.Equals(b.Curve))
throw new ArgumentException("Only points on the same curve can be added or subtracted");
// F2mFieldElement.CheckFieldElements(a.x, b.x);
}
internal static ECPoint ImplSumOfMultipliesGlv(ECPoint[] ps, BigInteger[] ks, GlvEndomorphism glvEndomorphism)
{
BigInteger n = ps[0].Curve.Order;
int len = ps.Length;
BigInteger[] abs = new BigInteger[len << 1];
for (int i = 0, j = 0; i < len; ++i)
{
BigInteger[] ab = glvEndomorphism.DecomposeScalar(ks[i].Mod(n));
abs[j++] = ab[0];
abs[j++] = ab[1];
}
ECPointMap pointMap = glvEndomorphism.PointMap;
if (glvEndomorphism.HasEfficientPointMap)
{
return ECAlgorithms.ImplSumOfMultiplies(ps, pointMap, abs);
}
ECPoint[] pqs = new ECPoint[len << 1];
for (int i = 0, j = 0; i < len; ++i)
{
ECPoint p = ps[i], q = pointMap.Map(p);
pqs[j++] = p;
pqs[j++] = q;
}
return ECAlgorithms.ImplSumOfMultiplies(pqs, abs);
}
public static ECPoint SumOfMultiplies(ECPoint[] ps, BigInteger[] ks)
{
if (ps == null || ks == null || ps.Length != ks.Length || ps.Length < 1)
throw new ArgumentException("point and scalar arrays should be non-null, and of equal, non-zero, length");
int count = ps.Length;
switch (count)
{
case 1:
return ps[0].Multiply(ks[0]);
case 2:
return SumOfTwoMultiplies(ps[0], ks[0], ps[1], ks[1]);
default:
break;
}
ECPoint p = ps[0];
ECCurve c = p.Curve;
ECPoint[] imported = new ECPoint[count];
imported[0] = p;
for (int i = 1; i < count; ++i)
{
imported[i] = ImportPoint(c, ps[i]);
}
GlvEndomorphism glvEndomorphism = c.GetEndomorphism() as GlvEndomorphism;
if (glvEndomorphism != null)
{
return ValidatePoint(ImplSumOfMultipliesGlv(imported, ks, glvEndomorphism));
}
return ValidatePoint(ImplSumOfMultiplies(imported, ks));
}
/* (non-Javadoc)
* @see BitcoinKit.BouncyCastle.math.ec.ECPoint#add(BitcoinKit.BouncyCastle.math.ec.ECPoint)
*/
public override ECPoint Add(ECPoint b)
{
CheckPoints(this, b);
return AddSimple((F2mPoint) b);
}
public override ECPoint TwicePlus(ECPoint b)
{
if (this == b)
return ThreeTimes();
if (this.IsInfinity)
return b;
if (b.IsInfinity)
return Twice();
ECFieldElement Y1 = this.RawYCoord;
if (Y1.IsZero)
return b;
ECCurve curve = this.Curve;
int coord = curve.CoordinateSystem;
switch (coord)
{
case ECCurve.COORD_AFFINE:
{
ECFieldElement X1 = this.RawXCoord;
ECFieldElement X2 = b.RawXCoord, Y2 = b.RawYCoord;
ECFieldElement dx = X2.Subtract(X1), dy = Y2.Subtract(Y1);
if (dx.IsZero)
{
if (dy.IsZero)
{
// this == b i.e. the result is 3P
return ThreeTimes();
}
// this == -b, i.e. the result is P
return this;
}
/*
* Optimized calculation of 2P + Q, as described in "Trading Inversions for
* Multiplications in Elliptic Curve Cryptography", by Ciet, Joye, Lauter, Montgomery.
*/
ECFieldElement X = dx.Square(), Y = dy.Square();
ECFieldElement d = X.Multiply(Two(X1).Add(X2)).Subtract(Y);
if (d.IsZero)
{
return Curve.Infinity;
}
ECFieldElement D = d.Multiply(dx);
ECFieldElement I = D.Invert();
ECFieldElement L1 = d.Multiply(I).Multiply(dy);
ECFieldElement L2 = Two(Y1).Multiply(X).Multiply(dx).Multiply(I).Subtract(L1);
ECFieldElement X4 = (L2.Subtract(L1)).Multiply(L1.Add(L2)).Add(X2);
ECFieldElement Y4 = (X1.Subtract(X4)).Multiply(L2).Subtract(Y1);
return new FpPoint(Curve, X4, Y4, IsCompressed);
}
case ECCurve.COORD_JACOBIAN_MODIFIED:
{
return TwiceJacobianModified(false).Add(b);
}
default:
{
return Twice().Add(b);
}
}
}