/**
* Multiplies a {@link noconflict.org.bouncycastle.math.ec.ECPoint.F2m ECPoint.F2m} by <code>k
* </code> using the reduced <code>τ</code>-adic NAF (RTNAF) method.
*
* @param p The ECPoint.F2m to multiply.
* @param k The integer by which to multiply <code>k</code>.
* @return <code>p</code> multiplied by <code>k</code>.
*/
public ECPoint multiply(ECPoint point, BigInteger k, PreCompInfo preCompInfo) {
if (!(point instanceof ECPoint.F2m)) {
throw new IllegalArgumentException("Only ECPoint.F2m can be " + "used in WTauNafMultiplier");
}
ECPoint.F2m p = (ECPoint.F2m) point;
ECCurve.F2m curve = (ECCurve.F2m) p.getCurve();
int m = curve.getM();
byte a = curve.getA().toBigInteger().byteValue();
byte mu = curve.getMu();
BigInteger[] s = curve.getSi();
ZTauElement rho = Tnaf.partModReduction(k, m, a, s, mu, (byte) 10);
return multiplyWTnaf(p, rho, preCompInfo, a, mu);
}
/**
* Multiplies a {@link noconflict.org.bouncycastle.math.ec.ECPoint.F2m ECPoint.F2m} by an element
* <code>λ</code> of <code><b>Z</b>[τ]</code> using the window <code>τ</code>-adic
* NAF (TNAF) method, given the WTNAF of <code>λ</code>.
*
* @param p The ECPoint.F2m to multiply.
* @param u The the WTNAF of <code>λ</code>..
* @return <code>λ * p</code>
*/
private static ECPoint.F2m multiplyFromWTnaf(ECPoint.F2m p, byte[] u, PreCompInfo preCompInfo) {
ECCurve.F2m curve = (ECCurve.F2m) p.getCurve();
byte a = curve.getA().toBigInteger().byteValue();
ECPoint.F2m[] pu;
if ((preCompInfo == null) || !(preCompInfo instanceof WTauNafPreCompInfo)) {
pu = Tnaf.getPreComp(p, a);
p.setPreCompInfo(new WTauNafPreCompInfo(pu));
} else {
pu = ((WTauNafPreCompInfo) preCompInfo).getPreComp();
}
// q = infinity
ECPoint.F2m q = (ECPoint.F2m) p.getCurve().getInfinity();
for (int i = u.length - 1; i >= 0; i--) {
q = Tnaf.tau(q);
if (u[i] != 0) {
if (u[i] > 0) {
q = q.addSimple(pu[u[i]]);
} else {
// u[i] < 0
q = q.subtractSimple(pu[-u[i]]);
}
}
}
return q;
}