Пример #1
0
/* return e.this */

    public ECP mul(BIG e)
    {
        if (e.iszilch() || is_infinity())
        {
            return(new ECP());
        }
        ECP P = new ECP();

        if (ROM.CURVETYPE == ROM.MONTGOMERY)
        {
/* use Ladder */
            int nb, i, b;
            ECP D  = new ECP();
            ECP R0 = new ECP();
            R0.copy(this);
            ECP R1 = new ECP();
            R1.copy(this);
            R1.dbl();
            D.copy(this);
            D.affine();
            nb = e.nbits();
            for (i = nb - 2; i >= 0; i--)
            {
                b = e.bit(i);
                P.copy(R1);
                P.dadd(R0, D);
                R0.cswap(R1, b);
                R1.copy(P);
                R0.dbl();
                R0.cswap(R1, b);
            }
            P.copy(R0);
        }
        else
        {
// fixed size windows
            int     i, b, nb, m, s, ns;
            BIG     mt = new BIG();
            BIG     t  = new BIG();
            ECP     Q  = new ECP();
            ECP     C  = new ECP();
            ECP[]   W  = new ECP[8];
            sbyte[] w  = new sbyte[1 + (ROM.NLEN * ROM.BASEBITS + 3) / 4];

            affine();

// precompute table
            Q.copy(this);
            Q.dbl();
            W[0] = new ECP();
            W[0].copy(this);

            for (i = 1; i < 8; i++)
            {
                W[i] = new ECP();
                W[i].copy(W[i - 1]);
                W[i].add(Q);
            }

// convert the table to affine
            if (ROM.CURVETYPE == ROM.WEIERSTRASS)
            {
                multiaffine(8, W);
            }

// make exponent odd - add 2P if even, P if odd
            t.copy(e);
            s = t.parity();
            t.inc(1);
            t.norm();
            ns = t.parity();
            mt.copy(t);
            mt.inc(1);
            mt.norm();
            t.cmove(mt, s);
            Q.cmove(this, ns);
            C.copy(Q);

            nb = 1 + (t.nbits() + 3) / 4;

// convert exponent to signed 4-bit window
            for (i = 0; i < nb; i++)
            {
                w[i] = (sbyte)(t.lastbits(5) - 16);
                t.dec(w[i]);
                t.norm();
                t.fshr(4);
            }
            w[nb] = (sbyte)t.lastbits(5);

            P.copy(W[(w[nb] - 1) / 2]);
            for (i = nb - 1; i >= 0; i--)
            {
                Q.select(W, w[i]);
                P.dbl();
                P.dbl();
                P.dbl();
                P.dbl();
                P.add(Q);
            }
            P.sub(C);             // apply correction
        }
        P.affine();
        return(P);
    }
Пример #2
0
/* Return e.this+f.Q */

    public ECP mul2(BIG e, ECP Q, BIG f)
    {
        BIG te = new BIG();
        BIG tf = new BIG();
        BIG mt = new BIG();
        ECP S  = new ECP();
        ECP T  = new ECP();
        ECP C  = new ECP();

        ECP[]   W = new ECP[8];
        sbyte[] w = new sbyte[1 + (ROM.NLEN * ROM.BASEBITS + 1) / 2];
        int     i, s, ns, nb;
        sbyte   a, b;

        affine();
        Q.affine();

        te.copy(e);
        tf.copy(f);

// precompute table
        W[1] = new ECP();
        W[1].copy(this);
        W[1].sub(Q);
        W[2] = new ECP();
        W[2].copy(this);
        W[2].add(Q);
        S.copy(Q);
        S.dbl();
        W[0] = new ECP();
        W[0].copy(W[1]);
        W[0].sub(S);
        W[3] = new ECP();
        W[3].copy(W[2]);
        W[3].add(S);
        T.copy(this);
        T.dbl();
        W[5] = new ECP();
        W[5].copy(W[1]);
        W[5].add(T);
        W[6] = new ECP();
        W[6].copy(W[2]);
        W[6].add(T);
        W[4] = new ECP();
        W[4].copy(W[5]);
        W[4].sub(S);
        W[7] = new ECP();
        W[7].copy(W[6]);
        W[7].add(S);

// convert the table to affine
        if (ROM.CURVETYPE == ROM.WEIERSTRASS)
        {
            multiaffine(8, W);
        }

// if multiplier is odd, add 2, else add 1 to multiplier, and add 2P or P to correction

        s = te.parity();
        te.inc(1);
        te.norm();
        ns = te.parity();
        mt.copy(te);
        mt.inc(1);
        mt.norm();
        te.cmove(mt, s);
        T.cmove(this, ns);
        C.copy(T);

        s = tf.parity();
        tf.inc(1);
        tf.norm();
        ns = tf.parity();
        mt.copy(tf);
        mt.inc(1);
        mt.norm();
        tf.cmove(mt, s);
        S.cmove(Q, ns);
        C.add(S);

        mt.copy(te);
        mt.add(tf);
        mt.norm();
        nb = 1 + (mt.nbits() + 1) / 2;

// convert exponent to signed 2-bit window
        for (i = 0; i < nb; i++)
        {
            a = (sbyte)(te.lastbits(3) - 4);
            te.dec(a);
            te.norm();
            te.fshr(2);
            b = (sbyte)(tf.lastbits(3) - 4);
            tf.dec(b);
            tf.norm();
            tf.fshr(2);
            w[i] = (sbyte)(4 * a + b);
        }
        w[nb] = (sbyte)(4 * te.lastbits(3) + tf.lastbits(3));
        S.copy(W[(w[nb] - 1) / 2]);

        for (i = nb - 1; i >= 0; i--)
        {
            T.select(W, w[i]);
            S.dbl();
            S.dbl();
            S.add(T);
        }
        S.sub(C);         // apply correction
        S.affine();
        return(S);
    }