FpNafMultiplier.cs :  » PDF » iTextSharp » Org » BouncyCastle » Math » EC » Multiplier » C# / CSharp Open Source

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)
      {             
        R = R.Twice();

        bool hBit = h.TestBit(i);
        bool eBit = e.TestBit(i);

        if (hBit != eBit)
        {
          R = R.Add(hBit ? p : neg);
        }
      }

      return R;
    }
  }
}