示例#1
0
            public PreCompInfo Precompute(PreCompInfo existing)
            {
                WNafPreCompInfo existingWNaf = existing as WNafPreCompInfo;

                int width         = m_fromWNaf.Width;
                int reqPreCompLen = m_fromWNaf.PreComp.Length;

                if (CheckExisting(existingWNaf, width, reqPreCompLen, m_includeNegated))
                {
                    existingWNaf.DecrementPromotionCountdown();
                    return(existingWNaf);
                }

                /*
                 * TODO Ideally this method would support incremental calculation, but given the
                 * existing use-cases it would be of little-to-no benefit.
                 */
                WNafPreCompInfo result = new WNafPreCompInfo();

                result.PromotionCountdown = m_fromWNaf.PromotionCountdown;

                ECPoint twiceFrom = m_fromWNaf.Twice;

                if (null != twiceFrom)
                {
                    ECPoint twice = m_pointMap.Map(twiceFrom);
                    result.Twice = twice;
                }

                ECPoint[] preCompFrom = m_fromWNaf.PreComp;
                ECPoint[] preComp     = new ECPoint[preCompFrom.Length];
                for (int i = 0; i < preCompFrom.Length; ++i)
                {
                    preComp[i] = m_pointMap.Map(preCompFrom[i]);
                }
                result.PreComp = preComp;
                result.Width   = width;

                if (m_includeNegated)
                {
                    ECPoint[] preCompNeg = new ECPoint[preComp.Length];
                    for (int i = 0; i < preCompNeg.Length; ++i)
                    {
                        preCompNeg[i] = preComp[i].Negate();
                    }
                    result.PreCompNeg = preCompNeg;
                }

                return(result);
            }
示例#2
0
            public PreCompInfo Precompute(PreCompInfo existing)
            {
                WNafPreCompInfo existingWNaf = existing as WNafPreCompInfo;

                int width         = System.Math.Max(2, System.Math.Min(MAX_WIDTH, m_minWidth));
                int reqPreCompLen = 1 << (width - 2);

                if (CheckExisting(existingWNaf, width, reqPreCompLen, m_includeNegated))
                {
                    existingWNaf.DecrementPromotionCountdown();
                    return(existingWNaf);
                }

                WNafPreCompInfo result = new WNafPreCompInfo();

                ECCurve c = m_p.Curve;

                ECPoint[] preComp = null, preCompNeg = null;
                ECPoint   twiceP  = null;

                if (null != existingWNaf)
                {
                    int promotionCountdown = existingWNaf.DecrementPromotionCountdown();
                    result.PromotionCountdown = promotionCountdown;

                    int confWidth = existingWNaf.ConfWidth;
                    result.ConfWidth = confWidth;

                    preComp    = existingWNaf.PreComp;
                    preCompNeg = existingWNaf.PreCompNeg;
                    twiceP     = existingWNaf.Twice;
                }

                width         = System.Math.Min(MAX_WIDTH, System.Math.Max(result.ConfWidth, width));
                reqPreCompLen = 1 << (width - 2);

                int iniPreCompLen = 0;

                if (null == preComp)
                {
                    preComp = EMPTY_POINTS;
                }
                else
                {
                    iniPreCompLen = preComp.Length;
                }

                if (iniPreCompLen < reqPreCompLen)
                {
                    preComp = WNafUtilities.ResizeTable(preComp, reqPreCompLen);

                    if (reqPreCompLen == 1)
                    {
                        preComp[0] = m_p.Normalize();
                    }
                    else
                    {
                        int curPreCompLen = iniPreCompLen;
                        if (curPreCompLen == 0)
                        {
                            preComp[0]    = m_p;
                            curPreCompLen = 1;
                        }

                        ECFieldElement iso = null;

                        if (reqPreCompLen == 2)
                        {
                            preComp[1] = m_p.ThreeTimes();
                        }
                        else
                        {
                            ECPoint isoTwiceP = twiceP, last = preComp[curPreCompLen - 1];
                            if (null == isoTwiceP)
                            {
                                isoTwiceP = preComp[0].Twice();
                                twiceP    = isoTwiceP;

                                /*
                                 * For Fp curves with Jacobian projective coordinates, use a (quasi-)isomorphism
                                 * where 'twiceP' is "affine", so that the subsequent additions are cheaper. This
                                 * also requires scaling the initial point's X, Y coordinates, and reversing the
                                 * isomorphism as part of the subsequent normalization.
                                 *
                                 *  NOTE: The correctness of this optimization depends on:
                                 *      1) additions do not use the curve's A, B coefficients.
                                 *      2) no special cases (i.e. Q +/- Q) when calculating 1P, 3P, 5P, ...
                                 */
                                if (!twiceP.IsInfinity && ECAlgorithms.IsFpCurve(c) && c.FieldSize >= 64)
                                {
                                    switch (c.CoordinateSystem)
                                    {
                                    case ECCurve.COORD_JACOBIAN:
                                    case ECCurve.COORD_JACOBIAN_CHUDNOVSKY:
                                    case ECCurve.COORD_JACOBIAN_MODIFIED:
                                    {
                                        iso       = twiceP.GetZCoord(0);
                                        isoTwiceP = c.CreatePoint(twiceP.XCoord.ToBigInteger(),
                                                                  twiceP.YCoord.ToBigInteger());

                                        ECFieldElement iso2 = iso.Square(), iso3 = iso2.Multiply(iso);
                                        last = last.ScaleX(iso2).ScaleY(iso3);

                                        if (iniPreCompLen == 0)
                                        {
                                            preComp[0] = last;
                                        }
                                        break;
                                    }
                                    }
                                }
                            }

                            while (curPreCompLen < reqPreCompLen)
                            {
                                /*
                                 * Compute the new ECPoints for the precomputation array. The values 1, 3,
                                 * 5, ..., 2^(width-1)-1 times p are computed
                                 */
                                preComp[curPreCompLen++] = last = last.Add(isoTwiceP);
                            }
                        }

                        /*
                         * Having oft-used operands in affine form makes operations faster.
                         */
                        c.NormalizeAll(preComp, iniPreCompLen, reqPreCompLen - iniPreCompLen, iso);
                    }
                }

                if (m_includeNegated)
                {
                    int pos;
                    if (null == preCompNeg)
                    {
                        pos        = 0;
                        preCompNeg = new ECPoint[reqPreCompLen];
                    }
                    else
                    {
                        pos = preCompNeg.Length;
                        if (pos < reqPreCompLen)
                        {
                            preCompNeg = WNafUtilities.ResizeTable(preCompNeg, reqPreCompLen);
                        }
                    }

                    while (pos < reqPreCompLen)
                    {
                        preCompNeg[pos] = preComp[pos].Negate();
                        ++pos;
                    }
                }

                result.PreComp    = preComp;
                result.PreCompNeg = preCompNeg;
                result.Twice      = twiceP;
                result.Width      = width;
                return(result);
            }