crypto/src/math/ec/multiplier/FpNafMultiplier.cs


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namespace Org.BouncyCastle.Math.EC.Multiplier
{
    /**
    * Class implementing the NAF (Non-Adjacent Form) multiplication algorithm.
    */
    internal class FpNafMultiplier
        : ECMultiplier
    {
        /**
        * D.3.2 pg 101
        * @see org.bouncycastle.math.ec.multiplier.ECMultiplier#multiply(org.bouncycastle.math.ec.ECPoint, java.math.BigInteger)
        */
        public ECPoint Multiply(ECPoint p, BigInteger k, PreCompInfo preCompInfo)
        {
            // TODO Probably should try to add this
            // BigInteger e = k.Mod(n); // n == order of p
            BigInteger e = k;
            BigInteger h = e.Multiply(BigInteger.Three);

            ECPoint neg = p.Negate();
            ECPoint R = p;

            for (int i = h.BitLength - 2; i > 0; --i)
            {             
                bool hBit = h.TestBit(i);
                bool eBit = e.TestBit(i);

                if (hBit == eBit)
                {
                    R = R.Twice();
                }
                else
                {
                    R = R.TwicePlus(hBit ? p : neg);
                }
            }

            return R;
        }
    }
}