64 lines
2.0 KiB
C#
64 lines
2.0 KiB
C#
#if !BESTHTTP_DISABLE_ALTERNATE_SSL && (!UNITY_WEBGL || UNITY_EDITOR)
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using System;
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namespace Org.BouncyCastle.Math.EC.Multiplier
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{
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public class FixedPointCombMultiplier
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: AbstractECMultiplier
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{
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protected override ECPoint MultiplyPositive(ECPoint p, BigInteger k)
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{
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ECCurve c = p.Curve;
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int size = FixedPointUtilities.GetCombSize(c);
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if (k.BitLength > size)
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{
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/*
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* TODO The comb works best when the scalars are less than the (possibly unknown) order.
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* Still, if we want to handle larger scalars, we could allow customization of the comb
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* size, or alternatively we could deal with the 'extra' bits either by running the comb
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* multiple times as necessary, or by using an alternative multiplier as prelude.
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*/
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throw new InvalidOperationException("fixed-point comb doesn't support scalars larger than the curve order");
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}
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int minWidth = GetWidthForCombSize(size);
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FixedPointPreCompInfo info = FixedPointUtilities.Precompute(p, minWidth);
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ECPoint[] lookupTable = info.PreComp;
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int width = info.Width;
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int d = (size + width - 1) / width;
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ECPoint R = c.Infinity;
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int top = d * width - 1;
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for (int i = 0; i < d; ++i)
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{
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int index = 0;
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for (int j = top - i; j >= 0; j -= d)
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{
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index <<= 1;
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if (k.TestBit(j))
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{
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index |= 1;
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}
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}
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R = R.TwicePlus(lookupTable[index]);
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}
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return R;
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}
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protected virtual int GetWidthForCombSize(int combSize)
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{
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return combSize > 257 ? 6 : 5;
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}
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}
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}
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#endif
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