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using System;
using System.Diagnostics;
using Org.BouncyCastle.Math.EC.Rfc8032;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Math.EC.Rfc7748
{
using F = X25519Field;
public static class X25519
{
public const int PointSize = 32;
public const int ScalarSize = 32;
private const int C_A = 486662;
private const int C_A24 = (C_A + 2)/4;
//private static readonly int[] SqrtNeg486664 = { 0x03457E06, 0x03812ABF, 0x01A82CC6, 0x028A5BE8, 0x018B43A7,
// 0x03FC4F7E, 0x02C23700, 0x006BBD27, 0x03A30500, 0x001E4DDB };
public static bool CalculateAgreement(byte[] k, int kOff, byte[] u, int uOff, byte[] r, int rOff)
{
ScalarMult(k, kOff, u, uOff, r, rOff);
return !Arrays.AreAllZeroes(r, rOff, PointSize);
}
private static uint Decode32(byte[] bs, int off)
{
uint n = bs[off];
n |= (uint)bs[++off] << 8;
n |= (uint)bs[++off] << 16;
n |= (uint)bs[++off] << 24;
return n;
}
private static void DecodeScalar(byte[] k, int kOff, uint[] n)
{
for (int i = 0; i < 8; ++i)
{
n[i] = Decode32(k, kOff + i * 4);
}
n[0] &= 0xFFFFFFF8U;
n[7] &= 0x7FFFFFFFU;
n[7] |= 0x40000000U;
}
public static void GeneratePrivateKey(SecureRandom random, byte[] k)
{
random.NextBytes(k);
k[0] &= 0xF8;
k[ScalarSize - 1] &= 0x7F;
k[ScalarSize - 1] |= 0x40;
}
public static void GeneratePublicKey(byte[] k, int kOff, byte[] r, int rOff)
{
ScalarMultBase(k, kOff, r, rOff);
}
private static void PointDouble(int[] x, int[] z)
{
int[] a = F.Create();
int[] b = F.Create();
F.Apm(x, z, a, b);
F.Sqr(a, a);
F.Sqr(b, b);
F.Mul(a, b, x);
F.Sub(a, b, a);
F.Mul(a, C_A24, z);
F.Add(z, b, z);
F.Mul(z, a, z);
}
public static void Precompute()
{
Ed25519.Precompute();
}
public static void ScalarMult(byte[] k, int kOff, byte[] u, int uOff, byte[] r, int rOff)
{
uint[] n = new uint[8]; DecodeScalar(k, kOff, n);
int[] x1 = F.Create(); F.Decode(u, uOff, x1);
int[] x2 = F.Create(); F.Copy(x1, 0, x2, 0);
int[] z2 = F.Create(); z2[0] = 1;
int[] x3 = F.Create(); x3[0] = 1;
int[] z3 = F.Create();
int[] t1 = F.Create();
int[] t2 = F.Create();
Debug.Assert(n[7] >> 30 == 1U);
int bit = 254, swap = 1;
do
{
F.Apm(x3, z3, t1, x3);
F.Apm(x2, z2, z3, x2);
F.Mul(t1, x2, t1);
F.Mul(x3, z3, x3);
F.Sqr(z3, z3);
F.Sqr(x2, x2);
F.Sub(z3, x2, t2);
F.Mul(t2, C_A24, z2);
F.Add(z2, x2, z2);
F.Mul(z2, t2, z2);
F.Mul(x2, z3, x2);
F.Apm(t1, x3, x3, z3);
F.Sqr(x3, x3);
F.Sqr(z3, z3);
F.Mul(z3, x1, z3);
--bit;
int word = bit >> 5, shift = bit & 0x1F;
int kt = (int)(n[word] >> shift) & 1;
swap ^= kt;
F.CSwap(swap, x2, x3);
F.CSwap(swap, z2, z3);
swap = kt;
}
while (bit >= 3);
Debug.Assert(swap == 0);
for (int i = 0; i < 3; ++i)
{
PointDouble(x2, z2);
}
F.Inv(z2, z2);
F.Mul(x2, z2, x2);
F.Normalize(x2);
F.Encode(x2, r, rOff);
}
public static void ScalarMultBase(byte[] k, int kOff, byte[] r, int rOff)
{
int[] y = F.Create();
int[] z = F.Create();
Ed25519.ScalarMultBaseYZ(k, kOff, y, z);
F.Apm(z, y, y, z);
F.Inv(z, z);
F.Mul(y, z, y);
F.Normalize(y);
F.Encode(y, r, rOff);
}
}
}
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