/*

 *  Copyright (C) 2021 - This file is part of libecc project

 *

 *  Authors:

 *      Ryad BENADJILA <ryadbenadjila@gmail.com>

 *      Arnaud EBALARD <arnaud.ebalard@ssi.gouv.fr>

 *

 *  This software is licensed under a dual BSD and GPL v2 license.

 *  See LICENSE file at the root folder of the project.

 */

#include <libecc/curves/ec_montgomery.h>

#define EC_MONTGOMERY_CRV_MAGIC ((word_t)(0x83734673a0443720ULL))

/* Check if a Montgomery curve is initialized.

 * Returns 0 on success, -1 on error.

 */

int ec_montgomery_crv_check_initialized(ec_montgomery_crv_src_t crv)

{

  int ret;

  MUST_HAVE((crv != NULL) && (crv->magic == EC_MONTGOMERY_CRV_MAGIC), ret, err);

  ret = 0;

err:

  return ret;

}

/*

 * Initialize pointed Montgomery curve structure using given A and B

 * Fp elements representing curve equation (B v^2 = u^3 + A u^2 + u) parameters.

 *

 * The function returns 0 on success, -1 on error.

 */

int ec_montgomery_crv_init(ec_montgomery_crv_t crv, fp_src_t A, fp_src_t B, nn_src_t order)

{

  int ret, iszero;

  fp tmp;

  tmp.magic = WORD(0);

  MUST_HAVE((crv != NULL), ret, err);

  ret = nn_check_initialized(order); EG(ret, err);

  ret = fp_check_initialized(A); EG(ret, err);

  ret = fp_check_initialized(B); EG(ret, err);

  MUST_HAVE(A->ctx == B->ctx, ret, err);

  ret = fp_init(&tmp, A->ctx); EG(ret, err);

  /* A and B elements of Fp, A unequal to (+/-)2 and B non zero */

  ret = fp_set_word_value(&tmp, 2); EG(ret, err);

  ret = fp_add(&tmp, A, &tmp); EG(ret, err);

  MUST_HAVE((!fp_iszero(&tmp, &iszero)) && (!iszero), ret, err);

  ret = fp_set_word_value(&tmp, 2); EG(ret, err);

  ret = fp_sub(&tmp, A, &tmp); EG(ret, err);

  MUST_HAVE((!fp_iszero(&tmp, &iszero)) && (!iszero), ret, err);

  MUST_HAVE((!fp_iszero(B, &iszero)) && (!iszero), ret, err);

  ret = fp_init(&(crv->A), A->ctx); EG(ret, err);

  ret = fp_init(&(crv->B), B->ctx); EG(ret, err);

  ret = fp_copy(&(crv->A), A); EG(ret, err);

  ret = fp_copy(&(crv->B), B); EG(ret, err);

  ret = nn_copy(&(crv->order), order); EG(ret, err);

  crv->magic = EC_MONTGOMERY_CRV_MAGIC;

err:

  fp_uninit(&tmp);

  return ret;

}

/* Uninitialize curve

 */

void ec_montgomery_crv_uninit(ec_montgomery_crv_t crv)

{

  if ((crv != NULL) && (crv->magic == EC_MONTGOMERY_CRV_MAGIC)) {

    crv->magic = WORD(0);

  }

  return;

}