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using System;
using System.Diagnostics;
using System.Runtime.CompilerServices;
namespace Org.BouncyCastle.Math.EC.Rfc7748
{
public abstract class X448
{
private const uint C_A = 156326;
private const uint C_A24 = (C_A + 2)/4;
// 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFE
private static readonly uint[] S_x = { 0x0FFFFFFEU, 0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFFU,
0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFEU, 0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFFU, 0x0FFFFFFFU,
0x0FFFFFFFU };
// 0xF0FAB725013244423ACF03881AFFEB7BDACDD1031C81B9672954459D84C1F823F1BD65643ACE1B5123AC33FF1C69BAF8ACB1197DC99D2720
private static readonly uint[] PsubS_x = { 0x099D2720U, 0x0B1197DCU, 0x09BAF8ACU, 0x033FF1C6U, 0x0B5123ACU,
0x0643ACE1U, 0x03F1BD65U, 0x084C1F82U, 0x0954459DU, 0x081B9672U, 0x0DD1031CU, 0x0EB7BDACU, 0x03881AFFU, 0x0423ACF0U,
0x05013244U, 0x0F0FAB72U };
private static uint[] precompBase = null;
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 < 14; ++i)
{
n[i] = Decode32(k, kOff + i * 4);
}
n[ 0] &= 0xFFFFFFFCU;
n[13] |= 0x80000000U;
}
private static void PointDouble(uint[] x, uint[] z)
{
uint[] A = X448Field.Create();
uint[] B = X448Field.Create();
//X448Field.Apm(x, z, A, B);
X448Field.Add(x, z, A);
X448Field.Sub(x, z, B);
X448Field.Sqr(A, A);
X448Field.Sqr(B, B);
X448Field.Mul(A, B, x);
X448Field.Sub(A, B, A);
X448Field.Mul(A, C_A24, z);
X448Field.Add(z, B, z);
X448Field.Mul(z, A, z);
}
// https://stackoverflow.com/questions/2223656/what-does-methodimploptions-synchronized-do
// Not available in lower .net standard versions
//[MethodImpl(MethodImplOptions.Synchronized)]
public static void Precompute()
{
lock (typeof(X448))
{
if (precompBase != null)
return;
precompBase = new uint[X448Field.Size * 446];
uint[] xs = precompBase;
uint[] zs = new uint[X448Field.Size * 445];
uint[] x = X448Field.Create(); x[0] = 5;
uint[] z = X448Field.Create(); z[0] = 1;
uint[] n = X448Field.Create();
uint[] d = X448Field.Create();
//X448Field.Apm(x, z, n, d);
X448Field.Add(x, z, n);
X448Field.Sub(x, z, d);
uint[] c = X448Field.Create(); X448Field.Copy(d, 0, c, 0);
int off = 0;
for (; ; )
{
X448Field.Copy(n, 0, xs, off);
if (off == (X448Field.Size * 445))
break;
PointDouble(x, z);
//X448Field.Apm(x, z, n, d);
X448Field.Add(x, z, n);
X448Field.Sub(x, z, d);
X448Field.Mul(n, c, n);
X448Field.Mul(c, d, c);
X448Field.Copy(d, 0, zs, off);
off += X448Field.Size;
}
uint[] u = X448Field.Create();
X448Field.Inv(c, u);
for (; ; )
{
X448Field.Copy(xs, off, x, 0);
X448Field.Mul(x, u, x);
//X448Field.Normalize(x);
X448Field.Copy(x, 0, precompBase, off);
if (off == 0)
break;
off -= X448Field.Size;
X448Field.Copy(zs, off, z, 0);
X448Field.Mul(u, z, u);
}
}
}
public static void ScalarMult(byte[] k, int kOff, byte[] u, int uOff, byte[] r, int rOff)
{
uint[] n = new uint[14]; DecodeScalar(k, kOff, n);
uint[] x1 = X448Field.Create(); X448Field.Decode(u, uOff, x1);
uint[] x2 = X448Field.Create(); X448Field.Copy(x1, 0, x2, 0);
uint[] z2 = X448Field.Create(); z2[0] = 1;
uint[] x3 = X448Field.Create(); x3[0] = 1;
uint[] z3 = X448Field.Create();
uint[] t1 = X448Field.Create();
uint[] t2 = X448Field.Create();
Debug.Assert(n[13] >> 31 == 1U);
int bit = 447, swap = 1;
do
{
//X448Field.Apm(x3, z3, t1, x3);
X448Field.Add(x3, z3, t1);
X448Field.Sub(x3, z3, x3);
//X448Field.Apm(x2, z2, z3, x2);
X448Field.Add(x2, z2, z3);
X448Field.Sub(x2, z2, x2);
X448Field.Mul(t1, x2, t1);
X448Field.Mul(x3, z3, x3);
X448Field.Sqr(z3, z3);
X448Field.Sqr(x2, x2);
X448Field.Sub(z3, x2, t2);
X448Field.Mul(t2, C_A24, z2);
X448Field.Add(z2, x2, z2);
X448Field.Mul(z2, t2, z2);
X448Field.Mul(x2, z3, x2);
//X448Field.Apm(t1, x3, x3, z3);
X448Field.Sub(t1, x3, z3);
X448Field.Add(t1, x3, x3);
X448Field.Sqr(x3, x3);
X448Field.Sqr(z3, z3);
X448Field.Mul(z3, x1, z3);
--bit;
int word = bit >> 5, shift = bit & 0x1F;
int kt = (int)(n[word] >> shift) & 1;
swap ^= kt;
X448Field.CSwap(swap, x2, x3);
X448Field.CSwap(swap, z2, z3);
swap = kt;
}
while (bit >= 2);
Debug.Assert(swap == 0);
for (int i = 0; i < 2; ++i)
{
PointDouble(x2, z2);
}
X448Field.Inv(z2, z2);
X448Field.Mul(x2, z2, x2);
X448Field.Normalize(x2);
X448Field.Encode(x2, r, rOff);
}
public static void ScalarMultBase(byte[] k, int kOff, byte[] r, int rOff)
{
Precompute();
uint[] n = new uint[14]; DecodeScalar(k, kOff, n);
uint[] x0 = X448Field.Create();
uint[] x1 = X448Field.Create(); X448Field.Copy(S_x, 0, x1, 0);
uint[] z1 = X448Field.Create(); z1[0] = 1;
uint[] x2 = X448Field.Create(); X448Field.Copy(PsubS_x, 0, x2, 0);
uint[] z2 = X448Field.Create(); z2[0] = 1;
uint[] A = X448Field.Create();
uint[] B = z1;
uint[] C = x0;
uint[] D = x1;
uint[] E = B;
Debug.Assert(n[13] >> 31 == 1U);
int off = 0, bit = 2, swap = 1;
do
{
X448Field.Copy(precompBase, off, x0, 0);
off += X448Field.Size;
int word = bit >> 5, shift = bit & 0x1F;
int kt = (int)(n[word] >> shift) & 1;
swap ^= kt;
X448Field.CSwap(swap, x1, x2);
X448Field.CSwap(swap, z1, z2);
swap = kt;
//X448Field.Apm(x1, z1, A, B);
X448Field.Add(x1, z1, A);
X448Field.Sub(x1, z1, B);
X448Field.Mul(x0, B, C);
X448Field.Carry(A);
//X448Field.Apm(A, C, D, E);
X448Field.Add(A, C, D);
X448Field.Sub(A, C, E);
X448Field.Sqr(D, D);
X448Field.Sqr(E, E);
X448Field.Mul(z2, D, x1);
X448Field.Mul(x2, E, z1);
}
while (++bit < 448);
Debug.Assert(swap == 1);
for (int i = 0; i < 2; ++i)
{
PointDouble(x1, z1);
}
X448Field.Inv(z1, z1);
X448Field.Mul(x1, z1, x1);
X448Field.Normalize(x1);
X448Field.Encode(x1, r, rOff);
}
}
}
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