org.bouncycastle.math.ec.WTauNafMultiplier Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of bcprov-ext-debug-jdk15on Show documentation
Show all versions of bcprov-ext-debug-jdk15on Show documentation
The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8 with debug enabled.
package org.bouncycastle.math.ec;
import java.math.BigInteger;
/**
* Class implementing the WTNAF (Window
* τ
-adic Non-Adjacent Form) algorithm.
*/
public class WTauNafMultiplier extends AbstractECMultiplier
{
// TODO Create WTauNafUtil class and move various functionality into it
static final String PRECOMP_NAME = "bc_wtnaf";
/**
* Multiplies a {@link org.bouncycastle.math.ec.ECPoint.AbstractF2m ECPoint.AbstractF2m}
* by k
using the reduced τ
-adic NAF (RTNAF)
* method.
* @param point The ECPoint.AbstractF2m to multiply.
* @param k The integer by which to multiply k
.
* @return p
multiplied by k
.
*/
protected ECPoint multiplyPositive(ECPoint point, BigInteger k)
{
if (!(point instanceof ECPoint.AbstractF2m))
{
throw new IllegalArgumentException("Only ECPoint.AbstractF2m can be " +
"used in WTauNafMultiplier");
}
ECPoint.AbstractF2m p = (ECPoint.AbstractF2m)point;
ECCurve.AbstractF2m curve = (ECCurve.AbstractF2m)p.getCurve();
int m = curve.getFieldSize();
byte a = curve.getA().toBigInteger().byteValue();
byte mu = Tnaf.getMu(a);
BigInteger[] s = curve.getSi();
ZTauElement rho = Tnaf.partModReduction(k, m, a, s, mu, (byte)10);
return multiplyWTnaf(p, rho, curve.getPreCompInfo(p, PRECOMP_NAME), a, mu);
}
/**
* Multiplies a {@link org.bouncycastle.math.ec.ECPoint.AbstractF2m ECPoint.AbstractF2m}
* by an element λ
of Z[τ]
using
* the τ
-adic NAF (TNAF) method.
* @param p The ECPoint.AbstractF2m to multiply.
* @param lambda The element λ
of
* Z[τ]
of which to compute the
* [τ]
-adic NAF.
* @return p
multiplied by λ
.
*/
private ECPoint.AbstractF2m multiplyWTnaf(ECPoint.AbstractF2m p, ZTauElement lambda,
PreCompInfo preCompInfo, byte a, byte mu)
{
ZTauElement[] alpha = (a == 0) ? Tnaf.alpha0 : Tnaf.alpha1;
BigInteger tw = Tnaf.getTw(mu, Tnaf.WIDTH);
byte[]u = Tnaf.tauAdicWNaf(mu, lambda, Tnaf.WIDTH,
BigInteger.valueOf(Tnaf.POW_2_WIDTH), tw, alpha);
return multiplyFromWTnaf(p, u, preCompInfo);
}
/**
* Multiplies a {@link org.bouncycastle.math.ec.ECPoint.AbstractF2m ECPoint.AbstractF2m}
* by an element λ
of Z[τ]
* using the window τ
-adic NAF (TNAF) method, given the
* WTNAF of λ
.
* @param p The ECPoint.AbstractF2m to multiply.
* @param u The the WTNAF of λ
..
* @return λ * p
*/
private static ECPoint.AbstractF2m multiplyFromWTnaf(ECPoint.AbstractF2m p, byte[] u, PreCompInfo preCompInfo)
{
ECCurve.AbstractF2m curve = (ECCurve.AbstractF2m)p.getCurve();
byte a = curve.getA().toBigInteger().byteValue();
ECPoint.AbstractF2m[] pu;
if ((preCompInfo == null) || !(preCompInfo instanceof WTauNafPreCompInfo))
{
pu = Tnaf.getPreComp(p, a);
WTauNafPreCompInfo pre = new WTauNafPreCompInfo();
pre.setPreComp(pu);
curve.setPreCompInfo(p, PRECOMP_NAME, pre);
}
else
{
pu = ((WTauNafPreCompInfo)preCompInfo).getPreComp();
}
// TODO Include negations in precomp (optionally) and use from here
ECPoint.AbstractF2m[] puNeg = new ECPoint.AbstractF2m[pu.length];
for (int i = 0; i < pu.length; ++i)
{
puNeg[i] = (ECPoint.AbstractF2m)pu[i].negate();
}
// q = infinity
ECPoint.AbstractF2m q = (ECPoint.AbstractF2m) p.getCurve().getInfinity();
int tauCount = 0;
for (int i = u.length - 1; i >= 0; i--)
{
++tauCount;
int ui = u[i];
if (ui != 0)
{
q = q.tauPow(tauCount);
tauCount = 0;
ECPoint x = ui > 0 ? pu[ui >>> 1] : puNeg[(-ui) >>> 1];
q = (ECPoint.AbstractF2m)q.add(x);
}
}
if (tauCount > 0)
{
q = q.tauPow(tauCount);
}
return q;
}
}
© 2015 - 2024 Weber Informatics LLC | Privacy Policy