// Copyright (c) 2014-2018 Zano Project
// Copyright (c) 2014-2018 The Louisdor Project
// Copyright (c) 2012-2013 The Boolberry developers
// Copyright (c) 2017-2025 Lethean (https://lt.hn)
//
// Licensed under the European Union Public Licence (EUPL) version 1.2.
// You may obtain a copy of the licence at:
//
//     https://joinup.ec.europa.eu/software/page/eupl/licence-eupl
//
// The EUPL is a copyleft licence that is compatible with the MIT/X11
// licence used by the original projects; the MIT terms are therefore
// considered “grandfathered” under the EUPL for this code.
//
// SPDX‑License‑Identifier: EUPL-1.2
//

/*
chacha-ref.c version 20080118
D. J. Bernstein
Public domain.
*/

#include "ecrypt-sync.h"

#define ROTATE(v,c) (ROTL32(v,c))
#define XOR(v,w) ((v) ^ (w))
#define PLUS(v,w) (U32V((v) + (w)))
#define PLUSONE(v) (PLUS((v),1))

#define QUARTERROUND(a,b,c,d) \
  x[a] = PLUS(x[a],x[b]); x[d] = ROTATE(XOR(x[d],x[a]),16); \
  x[c] = PLUS(x[c],x[d]); x[b] = ROTATE(XOR(x[b],x[c]),12); \
  x[a] = PLUS(x[a],x[b]); x[d] = ROTATE(XOR(x[d],x[a]), 8); \
  x[c] = PLUS(x[c],x[d]); x[b] = ROTATE(XOR(x[b],x[c]), 7);

static void salsa20_wordtobyte(u8 output[64], const u32 input[16])
{
  u32 x[16];
  int i;

  for (i = 0; i < 16; ++i) x[i] = input[i];
  for (i = 8; i > 0; i -= 2) {
    QUARTERROUND(0, 4, 8, 12)
      QUARTERROUND(1, 5, 9, 13)
      QUARTERROUND(2, 6, 10, 14)
      QUARTERROUND(3, 7, 11, 15)
      QUARTERROUND(0, 5, 10, 15)
      QUARTERROUND(1, 6, 11, 12)
      QUARTERROUND(2, 7, 8, 13)
      QUARTERROUND(3, 4, 9, 14)
  }
  for (i = 0; i < 16; ++i) x[i] = PLUS(x[i], input[i]);
  for (i = 0; i < 16; ++i) U32TO8_LITTLE(output + 4 * i, x[i]);
}

void ECRYPT_init(void)
{
  return;
}

static const char sigma[16] = "expand 32-byte k";
static const char tau[16] = "expand 16-byte k";

void ECRYPT_keysetup(ECRYPT_ctx *x, const u8 *k, u32 kbits, u32 ivbits)
{
  const char *constants;

  x->input[4] = U8TO32_LITTLE(k + 0);
  x->input[5] = U8TO32_LITTLE(k + 4);
  x->input[6] = U8TO32_LITTLE(k + 8);
  x->input[7] = U8TO32_LITTLE(k + 12);
  if (kbits == 256) { /* recommended */
    k += 16;
    constants = sigma;
  }
  else { /* kbits == 128 */
    constants = tau;
  }
  x->input[8] = U8TO32_LITTLE(k + 0);
  x->input[9] = U8TO32_LITTLE(k + 4);
  x->input[10] = U8TO32_LITTLE(k + 8);
  x->input[11] = U8TO32_LITTLE(k + 12);
  x->input[0] = U8TO32_LITTLE(constants + 0);
  x->input[1] = U8TO32_LITTLE(constants + 4);
  x->input[2] = U8TO32_LITTLE(constants + 8);
  x->input[3] = U8TO32_LITTLE(constants + 12);
}

void ECRYPT_ivsetup(ECRYPT_ctx *x, const u8 *iv)
{
  x->input[12] = 0;
  x->input[13] = 0;
  x->input[14] = U8TO32_LITTLE(iv + 0);
  x->input[15] = U8TO32_LITTLE(iv + 4);
}

void ECRYPT_encrypt_bytes(ECRYPT_ctx *x, const u8 *m, u8 *c, u32 bytes)
{
  u8 output[64];
  int i;

  if (!bytes) return;
  for (;;) {
    salsa20_wordtobyte(output, x->input);
    x->input[12] = PLUSONE(x->input[12]);
    if (!x->input[12]) {
      x->input[13] = PLUSONE(x->input[13]);
      /* stopping at 2^70 bytes per nonce is user's responsibility */
    }
    if (bytes <= 64) {
      for (i = 0; i < bytes; ++i) c[i] = m[i] ^ output[i];
      return;
    }
    for (i = 0; i < 64; ++i) c[i] = m[i] ^ output[i];
    bytes -= 64;
    c += 64;
    m += 64;
  }
}

void ECRYPT_decrypt_bytes(ECRYPT_ctx *x, const u8 *c, u8 *m, u32 bytes)
{
  ECRYPT_encrypt_bytes(x, c, m, bytes);
}

void ECRYPT_keystream_bytes(ECRYPT_ctx *x, u8 *stream, u32 bytes)
{
  u32 i;
  for (i = 0; i < bytes; ++i) stream[i] = 0;
  ECRYPT_encrypt_bytes(x, stream, stream, bytes);
}