/* Originally written by Bodo Moeller for the OpenSSL project.

 * ====================================================================

 * Copyright (c) 1998-2005 The OpenSSL Project.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 *

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in

 *    the documentation and/or other materials provided with the

 *    distribution.

 *

 * 3. All advertising materials mentioning features or use of this

 *    software must display the following acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"

 *

 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to

 *    endorse or promote products derived from this software without

 *    prior written permission. For written permission, please contact

 *    openssl-core@openssl.org.

 *

 * 5. Products derived from this software may not be called "OpenSSL"

 *    nor may "OpenSSL" appear in their names without prior written

 *    permission of the OpenSSL Project.

 *

 * 6. Redistributions of any form whatsoever must retain the following

 *    acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"

 *

 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY

 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR

 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,

 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED

 * OF THE POSSIBILITY OF SUCH DAMAGE.

 * ====================================================================

 *

 * This product includes cryptographic software written by Eric Young

 * (eay@cryptsoft.com).  This product includes software written by Tim

 * Hudson (tjh@cryptsoft.com).

 *

 */

/* ====================================================================

 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.

 *

 * Portions of the attached software ("Contribution") are developed by

 * SUN MICROSYSTEMS, INC., and are contributed to the OpenSSL project.

 *

 * The Contribution is licensed pursuant to the OpenSSL open source

 * license provided above.

 *

 * The elliptic curve binary polynomial software is originally written by

 * Sheueling Chang Shantz and Douglas Stebila of Sun Microsystems

 * Laboratories. */

#include <openssl/ec.h>

#include <openssl/bn.h>

#include <openssl/err.h>

#include "internal.h"

size_t ec_point_byte_len(const EC_GROUP *group, point_conversion_form_t form) {

  if (form != POINT_CONVERSION_COMPRESSED &&

      form != POINT_CONVERSION_UNCOMPRESSED) {

    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_FORM);

    return 0;

  }

  const size_t field_len = BN_num_bytes(&group->field.N);

  size_t output_len = 1 /* type byte */ + field_len;

  if (form == POINT_CONVERSION_UNCOMPRESSED) {

    // Uncompressed points have a second coordinate.

    output_len += field_len;

  }

  return output_len;

}

size_t ec_point_to_bytes(const EC_GROUP *group, const EC_AFFINE *point,

                         point_conversion_form_t form, uint8_t *buf,

                         size_t max_out) {

  size_t output_len = ec_point_byte_len(group, form);

  if (max_out < output_len) {

    OPENSSL_PUT_ERROR(EC, EC_R_BUFFER_TOO_SMALL);

    return 0;

  }

  size_t field_len;

  ec_felem_to_bytes(group, buf + 1, &field_len, &point->X);

  assert(field_len == BN_num_bytes(&group->field.N));

  if (form == POINT_CONVERSION_UNCOMPRESSED) {

    ec_felem_to_bytes(group, buf + 1 + field_len, &field_len, &point->Y);

    assert(field_len == BN_num_bytes(&group->field.N));

    buf[0] = form;

  } else {

    uint8_t y_buf[EC_MAX_BYTES];

    ec_felem_to_bytes(group, y_buf, &field_len, &point->Y);

    buf[0] = form + (y_buf[field_len - 1] & 1);

  }

  return output_len;

}

int ec_point_from_uncompressed(const EC_GROUP *group, EC_AFFINE *out,

                               const uint8_t *in, size_t len) {

  const size_t field_len = BN_num_bytes(&group->field.N);

  if (len != 1 + 2 * field_len || in[0] != POINT_CONVERSION_UNCOMPRESSED) {

    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_ENCODING);

    return 0;

  }

  EC_FELEM x, y;

  if (!ec_felem_from_bytes(group, &x, in + 1, field_len) ||

      !ec_felem_from_bytes(group, &y, in + 1 + field_len, field_len) ||

      !ec_point_set_affine_coordinates(group, out, &x, &y)) {

    return 0;

  }

  return 1;

}

static int ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,

                                   const uint8_t *buf, size_t len,

                                   BN_CTX *ctx) {

  if (len == 0) {

    OPENSSL_PUT_ERROR(EC, EC_R_BUFFER_TOO_SMALL);

    return 0;

  }

  point_conversion_form_t form = buf[0];

  if (form == POINT_CONVERSION_UNCOMPRESSED) {

    EC_AFFINE affine;

    if (!ec_point_from_uncompressed(group, &affine, buf, len)) {

      // In the event of an error, defend against the caller not checking the

      // return value by setting a known safe value.

      ec_set_to_safe_point(group, &point->raw);

      return 0;

    }

    ec_affine_to_jacobian(group, &point->raw, &affine);

    return 1;

  }

  const int y_bit = form & 1;

  const size_t field_len = BN_num_bytes(&group->field.N);

  form = form & ~1u;

  if (form != POINT_CONVERSION_COMPRESSED ||

      len != 1 /* type byte */ + field_len) {

    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_ENCODING);

    return 0;

  }

  // TODO(davidben): Integrate compressed coordinates with the lower-level EC

  // abstractions. This requires a way to compute square roots, which is tricky

  // for primes which are not 3 (mod 4), namely P-224 and custom curves. P-224's

  // prime is particularly inconvenient for compressed coordinates. See

  // https://cr.yp.to/papers/sqroot.pdf

  BN_CTX *new_ctx = NULL;

  if (ctx == NULL) {

    ctx = new_ctx = BN_CTX_new();

    if (ctx == NULL) {

      return 0;

    }

  }

  int ret = 0;

  BN_CTX_start(ctx);

  BIGNUM *x = BN_CTX_get(ctx);

  if (x == NULL || !BN_bin2bn(buf + 1, field_len, x)) {

    goto err;

  }

  if (BN_ucmp(x, &group->field.N) >= 0) {

    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_ENCODING);

    goto err;

  }

  if (!EC_POINT_set_compressed_coordinates_GFp(group, point, x, y_bit, ctx)) {

    goto err;

  }

  ret = 1;

err:

  BN_CTX_end(ctx);

  BN_CTX_free(new_ctx);

  return ret;

}

int EC_POINT_oct2point(const EC_GROUP *group, EC_POINT *point,

                       const uint8_t *buf, size_t len, BN_CTX *ctx) {

  if (EC_GROUP_cmp(group, point->group, NULL) != 0) {

    OPENSSL_PUT_ERROR(EC, EC_R_INCOMPATIBLE_OBJECTS);

    return 0;

  }

  return ec_GFp_simple_oct2point(group, point, buf, len, ctx);

}

size_t EC_POINT_point2oct(const EC_GROUP *group, const EC_POINT *point,

                          point_conversion_form_t form, uint8_t *buf,

                          size_t max_out, BN_CTX *ctx) {

  if (EC_GROUP_cmp(group, point->group, NULL) != 0) {

    OPENSSL_PUT_ERROR(EC, EC_R_INCOMPATIBLE_OBJECTS);

    return 0;

  }

  if (buf == NULL) {

    // When |buf| is NULL, just return the number of bytes that would be

    // written, without doing an expensive Jacobian-to-affine conversion.

    if (ec_GFp_simple_is_at_infinity(group, &point->raw)) {

      OPENSSL_PUT_ERROR(EC, EC_R_POINT_AT_INFINITY);

      return 0;

    }

    return ec_point_byte_len(group, form);

  }

  EC_AFFINE affine;

  if (!ec_jacobian_to_affine(group, &affine, &point->raw)) {

    return 0;

  }

  return ec_point_to_bytes(group, &affine, form, buf, max_out);

}

size_t EC_POINT_point2buf(const EC_GROUP *group, const EC_POINT *point,

                          point_conversion_form_t form, uint8_t **out_buf,

                          BN_CTX *ctx) {

  *out_buf = NULL;

  size_t len = EC_POINT_point2oct(group, point, form, NULL, 0, ctx);

  if (len == 0) {

    return 0;

  }

  uint8_t *buf = OPENSSL_malloc(len);

  if (buf == NULL) {

    return 0;

  }

  len = EC_POINT_point2oct(group, point, form, buf, len, ctx);

  if (len == 0) {

    OPENSSL_free(buf);

    return 0;

  }

  *out_buf = buf;

  return len;

}

int EC_POINT_set_compressed_coordinates_GFp(const EC_GROUP *group,

                                            EC_POINT *point, const BIGNUM *x,

                                            int y_bit, BN_CTX *ctx) {

  if (EC_GROUP_cmp(group, point->group, NULL) != 0) {

    OPENSSL_PUT_ERROR(EC, EC_R_INCOMPATIBLE_OBJECTS);

    return 0;

  }

  const BIGNUM *field = &group->field.N;

  if (BN_is_negative(x) || BN_cmp(x, field) >= 0) {

    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_COMPRESSED_POINT);

    return 0;

  }

  BN_CTX *new_ctx = NULL;

  int ret = 0;

  ERR_clear_error();

  if (ctx == NULL) {

    ctx = new_ctx = BN_CTX_new();

    if (ctx == NULL) {

      return 0;

    }

  }

  y_bit = (y_bit != 0);

  BN_CTX_start(ctx);

  BIGNUM *tmp1 = BN_CTX_get(ctx);

  BIGNUM *tmp2 = BN_CTX_get(ctx);

  BIGNUM *a = BN_CTX_get(ctx);

  BIGNUM *b = BN_CTX_get(ctx);

  BIGNUM *y = BN_CTX_get(ctx);

  if (y == NULL ||

      !EC_GROUP_get_curve_GFp(group, NULL, a, b, ctx)) {

    goto err;

  }

  // Recover y.  We have a Weierstrass equation

  //     y^2 = x^3 + a*x + b,

  // so  y  is one of the square roots of  x^3 + a*x + b.

  // tmp1 := x^3

  if (!BN_mod_sqr(tmp2, x, field, ctx) ||

      !BN_mod_mul(tmp1, tmp2, x, field, ctx)) {

    goto err;

  }

  // tmp1 := tmp1 + a*x

  if (group->a_is_minus3) {

    if (!bn_mod_lshift1_consttime(tmp2, x, field, ctx) ||

        !bn_mod_add_consttime(tmp2, tmp2, x, field, ctx) ||

        !bn_mod_sub_consttime(tmp1, tmp1, tmp2, field, ctx)) {

      goto err;

    }

  } else {

    if (!BN_mod_mul(tmp2, a, x, field, ctx) ||

        !bn_mod_add_consttime(tmp1, tmp1, tmp2, field, ctx)) {

      goto err;

    }

  }

  // tmp1 := tmp1 + b

  if (!bn_mod_add_consttime(tmp1, tmp1, b, field, ctx)) {

    goto err;

  }

  if (!BN_mod_sqrt(y, tmp1, field, ctx)) {

    uint32_t err = ERR_peek_last_error();

    if (ERR_GET_LIB(err) == ERR_LIB_BN &&

        ERR_GET_REASON(err) == BN_R_NOT_A_SQUARE) {

      ERR_clear_error();

      OPENSSL_PUT_ERROR(EC, EC_R_INVALID_COMPRESSED_POINT);

    } else {

      OPENSSL_PUT_ERROR(EC, ERR_R_BN_LIB);

    }

    goto err;

  }

  if (y_bit != BN_is_odd(y)) {

    if (BN_is_zero(y)) {

      OPENSSL_PUT_ERROR(EC, EC_R_INVALID_COMPRESSION_BIT);

      goto err;

    }

    if (!BN_usub(y, field, y)) {

      goto err;

    }

  }

  if (y_bit != BN_is_odd(y)) {

    OPENSSL_PUT_ERROR(EC, ERR_R_INTERNAL_ERROR);

    goto err;

  }

  if (!EC_POINT_set_affine_coordinates_GFp(group, point, x, y, ctx)) {

    goto err;

  }

  ret = 1;

err:

  BN_CTX_end(ctx);

  BN_CTX_free(new_ctx);

  return ret;

}