// Copyright 2010 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.

// Copyright 2007,2008  Segher Boessenkool  <segher@kernel.crashing.org>
// Licensed under the terms of the GNU GPL, version 2
// http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt

#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <string.h>

#include "Common/Common.h"
#include "Common/Crypto/bn.h"
#include "Common/Crypto/ec.h"

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4505)
#endif

// y**2 + x*y = x**3 + x + b
UNUSED static const u8 ec_b[30] = {0x00, 0x66, 0x64, 0x7e, 0xde, 0x6c, 0x33, 0x2c, 0x7f, 0x8c,
                                   0x09, 0x23, 0xbb, 0x58, 0x21, 0x3b, 0x33, 0x3b, 0x20, 0xe9,
                                   0xce, 0x42, 0x81, 0xfe, 0x11, 0x5f, 0x7d, 0x8f, 0x90, 0xad};

// order of the addition group of points
static const u8 ec_N[30] = {0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                            0x00, 0x00, 0x00, 0x00, 0x00, 0x13, 0xe9, 0x74, 0xe7, 0x2f,
                            0x8a, 0x69, 0x22, 0x03, 0x1d, 0x26, 0x03, 0xcf, 0xe0, 0xd7};

// base point
static const u8 ec_G[60] = {0x00, 0xfa, 0xc9, 0xdf, 0xcb, 0xac, 0x83, 0x13, 0xbb, 0x21, 0x39, 0xf1,
                            0xbb, 0x75, 0x5f, 0xef, 0x65, 0xbc, 0x39, 0x1f, 0x8b, 0x36, 0xf8, 0xf8,
                            0xeb, 0x73, 0x71, 0xfd, 0x55, 0x8b, 0x01, 0x00, 0x6a, 0x08, 0xa4, 0x19,
                            0x03, 0x35, 0x06, 0x78, 0xe5, 0x85, 0x28, 0xbe, 0xbf, 0x8a, 0x0b, 0xef,
                            0xf8, 0x67, 0xa7, 0xca, 0x36, 0x71, 0x6f, 0x7e, 0x01, 0xf8, 0x10, 0x52};

static void elt_copy(u8* d, const u8* a)
{
  memcpy(d, a, 30);
}

static void elt_zero(u8* d)
{
  memset(d, 0, 30);
}

static int elt_is_zero(const u8* d)
{
  u32 i;

  for (i = 0; i < 30; i++)
    if (d[i] != 0)
      return 0;

  return 1;
}

static void elt_add(u8* d, const u8* a, const u8* b)
{
  u32 i;

  for (i = 0; i < 30; i++)
    d[i] = a[i] ^ b[i];
}

static void elt_mul_x(u8* d, const u8* a)
{
  u8 carry, x, y;
  u32 i;

  carry = a[0] & 1;

  x = 0;
  for (i = 0; i < 29; i++)
  {
    y = a[i + 1];
    d[i] = x ^ (y >> 7);
    x = y << 1;
  }
  d[29] = x ^ carry;

  d[20] ^= carry << 2;
}

static void elt_mul(u8* d, const u8* a, const u8* b)
{
  u32 i, n;
  u8 mask;

  elt_zero(d);

  i = 0;
  mask = 1;
  for (n = 0; n < 233; n++)
  {
    elt_mul_x(d, d);

    if ((a[i] & mask) != 0)
      elt_add(d, d, b);

    mask >>= 1;
    if (mask == 0)
    {
      mask = 0x80;
      i++;
    }
  }
}

static const u8 square[16] = {0x00, 0x01, 0x04, 0x05, 0x10, 0x11, 0x14, 0x15,
                              0x40, 0x41, 0x44, 0x45, 0x50, 0x51, 0x54, 0x55};

static void elt_square_to_wide(u8* d, const u8* a)
{
  u32 i;

  for (i = 0; i < 30; i++)
  {
    d[2 * i] = square[a[i] >> 4];
    d[2 * i + 1] = square[a[i] & 15];
  }
}

static void wide_reduce(u8* d)
{
  u32 i;
  u8 x;

  for (i = 0; i < 30; i++)
  {
    x = d[i];

    d[i + 19] ^= x >> 7;
    d[i + 20] ^= x << 1;

    d[i + 29] ^= x >> 1;
    d[i + 30] ^= x << 7;
  }

  x = d[30] & ~1;

  d[49] ^= x >> 7;
  d[50] ^= x << 1;

  d[59] ^= x >> 1;

  d[30] &= 1;
}

static void elt_square(u8* d, const u8* a)
{
  u8 wide[60];

  elt_square_to_wide(wide, a);
  wide_reduce(wide);

  elt_copy(d, wide + 30);
}

static void itoh_tsujii(u8* d, const u8* a, const u8* b, u32 j)
{
  u8 t[30];

  elt_copy(t, a);
  while (j--)
  {
    elt_square(d, t);
    elt_copy(t, d);
  }

  elt_mul(d, t, b);
}

static void elt_inv(u8* d, const u8* a)
{
  u8 t[30];
  u8 s[30];

  itoh_tsujii(t, a, a, 1);
  itoh_tsujii(s, t, a, 1);
  itoh_tsujii(t, s, s, 3);
  itoh_tsujii(s, t, a, 1);
  itoh_tsujii(t, s, s, 7);
  itoh_tsujii(s, t, t, 14);
  itoh_tsujii(t, s, a, 1);
  itoh_tsujii(s, t, t, 29);
  itoh_tsujii(t, s, s, 58);
  itoh_tsujii(s, t, t, 116);
  elt_square(d, s);
}

UNUSED static int point_is_on_curve(u8* p)
{
  u8 s[30], t[30];
  u8 *x, *y;

  x = p;
  y = p + 30;

  elt_square(t, x);
  elt_mul(s, t, x);

  elt_add(s, s, t);

  elt_square(t, y);
  elt_add(s, s, t);

  elt_mul(t, x, y);
  elt_add(s, s, t);

  elt_add(s, s, ec_b);

  return elt_is_zero(s);
}

static int point_is_zero(const u8* p)
{
  return elt_is_zero(p) && elt_is_zero(p + 30);
}

static void point_double(u8* r, const u8* p)
{
  u8 s[30], t[30];
  const u8 *px, *py;
  u8 *rx, *ry;

  px = p;
  py = p + 30;
  rx = r;
  ry = r + 30;

  if (elt_is_zero(px))
  {
    elt_zero(rx);
    elt_zero(ry);

    return;
  }

  elt_inv(t, px);
  elt_mul(s, py, t);
  elt_add(s, s, px);

  elt_square(t, px);

  elt_square(rx, s);
  elt_add(rx, rx, s);
  rx[29] ^= 1;

  elt_mul(ry, s, rx);
  elt_add(ry, ry, rx);
  elt_add(ry, ry, t);
}

static void point_add(u8* r, const u8* p, const u8* q)
{
  u8 s[30], t[30], u[30];
  const u8 *px, *py, *qx, *qy;
  u8 *rx, *ry;

  px = p;
  py = p + 30;
  qx = q;
  qy = q + 30;
  rx = r;
  ry = r + 30;

  if (point_is_zero(p))
  {
    elt_copy(rx, qx);
    elt_copy(ry, qy);
    return;
  }

  if (point_is_zero(q))
  {
    elt_copy(rx, px);
    elt_copy(ry, py);
    return;
  }

  elt_add(u, px, qx);

  if (elt_is_zero(u))
  {
    elt_add(u, py, qy);
    if (elt_is_zero(u))
      point_double(r, p);
    else
    {
      elt_zero(rx);
      elt_zero(ry);
    }

    return;
  }

  elt_inv(t, u);
  elt_add(u, py, qy);
  elt_mul(s, t, u);

  elt_square(t, s);
  elt_add(t, t, s);
  elt_add(t, t, qx);
  t[29] ^= 1;

  elt_mul(u, s, t);
  elt_add(s, u, py);
  elt_add(rx, t, px);
  elt_add(ry, s, rx);
}

void point_mul(u8* d, const u8* a, const u8* b)  // a is bignum
{
  u32 i;
  u8 mask;

  elt_zero(d);
  elt_zero(d + 30);

  for (i = 0; i < 30; i++)
    for (mask = 0x80; mask != 0; mask >>= 1)
    {
      point_double(d, d);
      if ((a[i] & mask) != 0)
        point_add(d, d, b);
    }
}

static void silly_random(u8* rndArea, u8 count)
{
  u16 i;
  srand((unsigned)(time(nullptr)));

  for (i = 0; i < count; i++)
  {
    rndArea[i] = rand();
  }
}

void generate_ecdsa(u8* R, u8* S, const u8* k, const u8* hash)
{
  u8 e[30];
  u8 kk[30];
  u8 m[30];
  u8 minv[30];
  u8 mG[60];
  // FILE *fp;

  elt_zero(e);
  memcpy(e + 10, hash, 20);

  // Changing random number generator to a lame one...
  silly_random(m, sizeof(m));
  // fp = fopen("/dev/random", "rb");
  // if (fread(m, sizeof m, 1, fp) != 1)
  //	fatal("reading random");
  // fclose(fp);
  m[0] = 0;

  //	R = (mG).x

  point_mul(mG, m, ec_G);
  elt_copy(R, mG);
  if (bn_compare(R, ec_N, 30) >= 0)
    bn_sub_modulus(R, ec_N, 30);

  //	S = m**-1*(e + Rk) (mod N)

  elt_copy(kk, k);
  if (bn_compare(kk, ec_N, 30) >= 0)
    bn_sub_modulus(kk, ec_N, 30);
  bn_mul(S, R, kk, ec_N, 30);
  bn_add(kk, S, e, ec_N, 30);
  bn_inv(minv, m, ec_N, 30);
  bn_mul(S, minv, kk, ec_N, 30);
}

UNUSED static int check_ecdsa(u8* Q, u8* R, u8* S, const u8* hash)
{
  u8 Sinv[30];
  u8 e[30];
  u8 w1[30], w2[30];
  u8 r1[60], r2[60];

  bn_inv(Sinv, S, ec_N, 30);

  elt_zero(e);
  memcpy(e + 10, hash, 20);

  bn_mul(w1, e, Sinv, ec_N, 30);
  bn_mul(w2, R, Sinv, ec_N, 30);

  point_mul(r1, w1, ec_G);
  point_mul(r2, w2, Q);

  point_add(r1, r1, r2);

  if (bn_compare(r1, ec_N, 30) >= 0)
    bn_sub_modulus(r1, ec_N, 30);

  return (bn_compare(r1, R, 30) == 0);
}

void ec_priv_to_pub(const u8* k, u8* Q)
{
  point_mul(Q, k, ec_G);
}

#ifdef _MSC_VER
#pragma warning(pop)
#endif