Source Code Cross Referenced for WTauNafMultiplier.java in  » Security » Bouncy-Castle » org » bouncycastle » math » ec » Java Source Code / Java DocumentationJava Source Code and Java Documentation

001:        package org.bouncycastle.math.ec;
002:
003:        import java.math.BigInteger;
004:
005:        /**
006:         * Class implementing the WTNAF (Window
007:         * <code>&tau;</code>-adic Non-Adjacent Form) algorithm.
008:         */
009:        class WTauNafMultiplier implements  ECMultiplier {
010:            /**
011:             * Multiplies a {@link org.bouncycastle.math.ec.ECPoint.F2m ECPoint.F2m}
012:             * by <code>k</code> using the reduced <code>&tau;</code>-adic NAF (RTNAF)
013:             * method.
014:             * @param p The ECPoint.F2m to multiply.
015:             * @param k The integer by which to multiply <code>k</code>.
016:             * @return <code>p</code> multiplied by <code>k</code>.
017:             */
018:            public ECPoint multiply(ECPoint point, BigInteger k,
019:                    PreCompInfo preCompInfo) {
020:                if (!(point instanceof  ECPoint.F2m)) {
021:                    throw new IllegalArgumentException(
022:                            "Only ECPoint.F2m can be "
023:                                    + "used in WTauNafMultiplier");
024:                }
025:
026:                ECPoint.F2m p = (ECPoint.F2m) point;
027:
028:                ECCurve.F2m curve = (ECCurve.F2m) p.getCurve();
029:                int m = curve.getM();
030:                byte a = curve.getA().toBigInteger().byteValue();
031:                byte mu = curve.getMu();
032:                BigInteger[] s = curve.getSi();
033:
034:                ZTauElement rho = Tnaf.partModReduction(k, m, a, s, mu,
035:                        (byte) 10);
036:
037:                return multiplyWTnaf(p, rho, preCompInfo, a, mu);
038:            }
039:
040:            /**
041:             * Multiplies a {@link org.bouncycastle.math.ec.ECPoint.F2m ECPoint.F2m}
042:             * by an element <code>&lambda;</code> of <code><b>Z</b>[&tau;]</code> using
043:             * the <code>&tau;</code>-adic NAF (TNAF) method.
044:             * @param p The ECPoint.F2m to multiply.
045:             * @param lambda The element <code>&lambda;</code> of
046:             * <code><b>Z</b>[&tau;]</code> of which to compute the
047:             * <code>[&tau;]</code>-adic NAF.
048:             * @return <code>p</code> multiplied by <code>&lambda;</code>.
049:             */
050:            private ECPoint.F2m multiplyWTnaf(ECPoint.F2m p,
051:                    ZTauElement lambda, PreCompInfo preCompInfo, byte a, byte mu) {
052:                ZTauElement[] alpha;
053:                if (a == 0) {
054:                    alpha = Tnaf.alpha0;
055:                } else {
056:                    // a == 1
057:                    alpha = Tnaf.alpha1;
058:                }
059:
060:                BigInteger tw = Tnaf.getTw(mu, Tnaf.WIDTH);
061:
062:                byte[] u = Tnaf.tauAdicWNaf(mu, lambda, Tnaf.WIDTH, BigInteger
063:                        .valueOf(Tnaf.POW_2_WIDTH), tw, alpha);
064:
065:                return multiplyFromWTnaf(p, u, preCompInfo);
066:            }
067:
068:            /**
069:             * Multiplies a {@link org.bouncycastle.math.ec.ECPoint.F2m ECPoint.F2m}
070:             * by an element <code>&lambda;</code> of <code><b>Z</b>[&tau;]</code>
071:             * using the window <code>&tau;</code>-adic NAF (TNAF) method, given the
072:             * WTNAF of <code>&lambda;</code>.
073:             * @param p The ECPoint.F2m to multiply.
074:             * @param u The the WTNAF of <code>&lambda;</code>..
075:             * @return <code>&lambda; * p</code>
076:             */
077:            private static ECPoint.F2m multiplyFromWTnaf(ECPoint.F2m p,
078:                    byte[] u, PreCompInfo preCompInfo) {
079:                ECCurve.F2m curve = (ECCurve.F2m) p.getCurve();
080:                byte a = curve.getA().toBigInteger().byteValue();
081:
082:                ECPoint.F2m[] pu;
083:                if ((preCompInfo == null)
084:                        || !(preCompInfo instanceof  WTauNafPreCompInfo)) {
085:                    pu = Tnaf.getPreComp(p, a);
086:                    p.setPreCompInfo(new WTauNafPreCompInfo(pu));
087:                } else {
088:                    pu = ((WTauNafPreCompInfo) preCompInfo).getPreComp();
089:                }
090:
091:                // q = infinity
092:                ECPoint.F2m q = (ECPoint.F2m) p.getCurve().getInfinity();
093:                for (int i = u.length - 1; i >= 0; i--) {
094:                    q = Tnaf.tau(q);
095:                    if (u[i] != 0) {
096:                        if (u[i] > 0) {
097:                            q = q.addSimple(pu[u[i]]);
098:                        } else {
099:                            // u[i] < 0
100:                            q = q.subtractSimple(pu[-u[i]]);
101:                        }
102:                    }
103:                }
104:
105:                return q;
106:            }
107:        }