| /* GENERATED SOURCE. DO NOT MODIFY. */ |
| package com.android.org.bouncycastle.math.ec; |
| |
| import java.math.BigInteger; |
| |
| /** |
| * Class implementing the WTNAF (Window |
| * <code>τ</code>-adic Non-Adjacent Form) algorithm. |
| * @hide This class is not part of the Android public SDK API |
| */ |
| 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 com.android.org.bouncycastle.math.ec.ECPoint.AbstractF2m ECPoint.AbstractF2m} |
| * by <code>k</code> using the reduced <code>τ</code>-adic NAF (RTNAF) |
| * method. |
| * @param point The ECPoint.AbstractF2m to multiply. |
| * @param k The integer by which to multiply <code>k</code>. |
| * @return <code>p</code> multiplied by <code>k</code>. |
| */ |
| 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, a, mu); |
| } |
| |
| /** |
| * Multiplies a {@link com.android.org.bouncycastle.math.ec.ECPoint.AbstractF2m ECPoint.AbstractF2m} |
| * by an element <code>λ</code> of <code><b>Z</b>[τ]</code> using |
| * the <code>τ</code>-adic NAF (TNAF) method. |
| * @param p The ECPoint.AbstractF2m to multiply. |
| * @param lambda The element <code>λ</code> of |
| * <code><b>Z</b>[τ]</code> of which to compute the |
| * <code>[τ]</code>-adic NAF. |
| * @return <code>p</code> multiplied by <code>λ</code>. |
| */ |
| private ECPoint.AbstractF2m multiplyWTnaf(ECPoint.AbstractF2m p, ZTauElement lambda, 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); |
| } |
| |
| /** |
| * Multiplies a {@link com.android.org.bouncycastle.math.ec.ECPoint.AbstractF2m ECPoint.AbstractF2m} |
| * 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.AbstractF2m to multiply. |
| * @param u The the WTNAF of <code>λ</code>.. |
| * @return <code>λ * p</code> |
| */ |
| private static ECPoint.AbstractF2m multiplyFromWTnaf(final ECPoint.AbstractF2m p, byte[] u) |
| { |
| ECCurve.AbstractF2m curve = (ECCurve.AbstractF2m)p.getCurve(); |
| final byte a = curve.getA().toBigInteger().byteValue(); |
| |
| WTauNafPreCompInfo preCompInfo = (WTauNafPreCompInfo)curve.precompute(p, PRECOMP_NAME, new PreCompCallback() |
| { |
| public PreCompInfo precompute(PreCompInfo existing) |
| { |
| if (existing instanceof WTauNafPreCompInfo) |
| { |
| return existing; |
| } |
| |
| WTauNafPreCompInfo result = new WTauNafPreCompInfo(); |
| result.setPreComp(Tnaf.getPreComp(p, a)); |
| return result; |
| } |
| }); |
| |
| ECPoint.AbstractF2m[] pu = 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; |
| } |
| } |