openssl/crypto/ec/ecp_smpl.c

/* crypto/ec/ecp_smpl.c */
/*
 * Includes code written by Lenka Fibikova <fibikova@exp-math.uni-essen.de>
 * for the OpenSSL project. Includes code written by Bodo Moeller for the
 * OpenSSL project.
 */
/* ====================================================================
 * Copyright (c) 1998-2002 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 this software developed by SUN MICROSYSTEMS, INC.,
 * and contributed to the OpenSSL project.
 */

#include <openssl/err.h>
#include <openssl/symhacks.h>

#include "ec_lcl.h"

const EC_METHOD *EC_GFp_simple_method(void)
{
    static const EC_METHOD ret = {
        NID_X9_62_prime_field,
        ec_GFp_simple_group_init,
        ec_GFp_simple_group_finish,
        ec_GFp_simple_group_clear_finish,
        ec_GFp_simple_group_copy,
        ec_GFp_simple_group_set_curve,
        ec_GFp_simple_group_get_curve,
        ec_GFp_simple_group_get_degree,
        ec_GFp_simple_group_check_discriminant,
        ec_GFp_simple_point_init,
        ec_GFp_simple_point_finish,
        ec_GFp_simple_point_clear_finish,
        ec_GFp_simple_point_copy,
        ec_GFp_simple_point_set_to_infinity,
        ec_GFp_simple_set_Jprojective_coordinates_GFp,
        ec_GFp_simple_get_Jprojective_coordinates_GFp,
        ec_GFp_simple_point_set_affine_coordinates,
        ec_GFp_simple_point_get_affine_coordinates,
        ec_GFp_simple_set_compressed_coordinates,
        ec_GFp_simple_point2oct,
        ec_GFp_simple_oct2point,
        ec_GFp_simple_add,
        ec_GFp_simple_dbl,
        ec_GFp_simple_invert,
        ec_GFp_simple_is_at_infinity,
        ec_GFp_simple_is_on_curve,
        ec_GFp_simple_cmp,
        ec_GFp_simple_make_affine,
        ec_GFp_simple_points_make_affine,
        0 /* mul */ ,
        0 /* precompute_mult */ ,
        0 /* have_precompute_mult */ ,
        ec_GFp_simple_field_mul,
        ec_GFp_simple_field_sqr,
        0 /* field_div */ ,
        0 /* field_encode */ ,
        0 /* field_decode */ ,
        0                       /* field_set_to_one */
    };

    return &ret;
}

/*
 * Most method functions in this file are designed to work with
 * non-trivial representations of field elements if necessary
 * (see ecp_mont.c): while standard modular addition and subtraction
 * are used, the field_mul and field_sqr methods will be used for
 * multiplication, and field_encode and field_decode (if defined)
 * will be used for converting between representations.
 *
 * Functions ec_GFp_simple_points_make_affine() and
 * ec_GFp_simple_point_get_affine_coordinates() specifically assume
 * that if a non-trivial representation is used, it is a Montgomery
 * representation (i.e. 'encoding' means multiplying by some factor R).
 */

int ec_GFp_simple_group_init(EC_GROUP *group)
{
    BN_init(&group->field);
    BN_init(&group->a);
    BN_init(&group->b);
    group->a_is_minus3 = 0;
    return 1;
}

void ec_GFp_simple_group_finish(EC_GROUP *group)
{
    BN_free(&group->field);
    BN_free(&group->a);
    BN_free(&group->b);
}

void ec_GFp_simple_group_clear_finish(EC_GROUP *group)
{
    BN_clear_free(&group->field);
    BN_clear_free(&group->a);
    BN_clear_free(&group->b);
}

int ec_GFp_simple_group_copy(EC_GROUP *dest, const EC_GROUP *src)
{
    if (!BN_copy(&dest->field, &src->field))
        return 0;
    if (!BN_copy(&dest->a, &src->a))
        return 0;
    if (!BN_copy(&dest->b, &src->b))
        return 0;

    dest->a_is_minus3 = src->a_is_minus3;

    return 1;
}

int ec_GFp_simple_group_set_curve(EC_GROUP *group,
                                  const BIGNUM *p, const BIGNUM *a,
                                  const BIGNUM *b, BN_CTX *ctx)
{
    int ret = 0;
    BN_CTX *new_ctx = NULL;
    BIGNUM *tmp_a;

    /* p must be a prime > 3 */
    if (BN_num_bits(p) <= 2 || !BN_is_odd(p)) {
        ECerr(EC_F_EC_GFP_SIMPLE_GROUP_SET_CURVE, EC_R_INVALID_FIELD);
        return 0;
    }

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    BN_CTX_start(ctx);
    tmp_a = BN_CTX_get(ctx);
    if (tmp_a == NULL)
        goto err;

    /* group->field */
    if (!BN_copy(&group->field, p))
        goto err;
    BN_set_negative(&group->field, 0);

    /* group->a */
    if (!BN_nnmod(tmp_a, a, p, ctx))
        goto err;
    if (group->meth->field_encode) {
        if (!group->meth->field_encode(group, &group->a, tmp_a, ctx))
            goto err;
    } else if (!BN_copy(&group->a, tmp_a))
        goto err;

    /* group->b */
    if (!BN_nnmod(&group->b, b, p, ctx))
        goto err;
    if (group->meth->field_encode)
        if (!group->meth->field_encode(group, &group->b, &group->b, ctx))
            goto err;

    /* group->a_is_minus3 */
    if (!BN_add_word(tmp_a, 3))
        goto err;
    group->a_is_minus3 = (0 == BN_cmp(tmp_a, &group->field));

    ret = 1;

 err:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_group_get_curve(const EC_GROUP *group, BIGNUM *p, BIGNUM *a,
                                  BIGNUM *b, BN_CTX *ctx)
{
    int ret = 0;
    BN_CTX *new_ctx = NULL;

    if (p != NULL) {
        if (!BN_copy(p, &group->field))
            return 0;
    }

    if (a != NULL || b != NULL) {
        if (group->meth->field_decode) {
            if (ctx == NULL) {
                ctx = new_ctx = BN_CTX_new();
                if (ctx == NULL)
                    return 0;
            }
            if (a != NULL) {
                if (!group->meth->field_decode(group, a, &group->a, ctx))
                    goto err;
            }
            if (b != NULL) {
                if (!group->meth->field_decode(group, b, &group->b, ctx))
                    goto err;
            }
        } else {
            if (a != NULL) {
                if (!BN_copy(a, &group->a))
                    goto err;
            }
            if (b != NULL) {
                if (!BN_copy(b, &group->b))
                    goto err;
            }
        }
    }

    ret = 1;

 err:
    if (new_ctx)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_group_get_degree(const EC_GROUP *group)
{
    return BN_num_bits(&group->field);
}

int ec_GFp_simple_group_check_discriminant(const EC_GROUP *group, BN_CTX *ctx)
{
    int ret = 0;
    BIGNUM *a, *b, *order, *tmp_1, *tmp_2;
    const BIGNUM *p = &group->field;
    BN_CTX *new_ctx = NULL;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL) {
            ECerr(EC_F_EC_GFP_SIMPLE_GROUP_CHECK_DISCRIMINANT,
                  ERR_R_MALLOC_FAILURE);
            goto err;
        }
    }
    BN_CTX_start(ctx);
    a = BN_CTX_get(ctx);
    b = BN_CTX_get(ctx);
    tmp_1 = BN_CTX_get(ctx);
    tmp_2 = BN_CTX_get(ctx);
    order = BN_CTX_get(ctx);
    if (order == NULL)
        goto err;

    if (group->meth->field_decode) {
        if (!group->meth->field_decode(group, a, &group->a, ctx))
            goto err;
        if (!group->meth->field_decode(group, b, &group->b, ctx))
            goto err;
    } else {
        if (!BN_copy(a, &group->a))
            goto err;
        if (!BN_copy(b, &group->b))
            goto err;
    }

    /*-
     * check the discriminant:
     * y^2 = x^3 + a*x + b is an elliptic curve <=> 4*a^3 + 27*b^2 != 0 (mod p)
     * 0 =< a, b < p
     */
    if (BN_is_zero(a)) {
        if (BN_is_zero(b))
            goto err;
    } else if (!BN_is_zero(b)) {
        if (!BN_mod_sqr(tmp_1, a, p, ctx))
            goto err;
        if (!BN_mod_mul(tmp_2, tmp_1, a, p, ctx))
            goto err;
        if (!BN_lshift(tmp_1, tmp_2, 2))
            goto err;
        /* tmp_1 = 4*a^3 */

        if (!BN_mod_sqr(tmp_2, b, p, ctx))
            goto err;
        if (!BN_mul_word(tmp_2, 27))
            goto err;
        /* tmp_2 = 27*b^2 */

        if (!BN_mod_add(a, tmp_1, tmp_2, p, ctx))
            goto err;
        if (BN_is_zero(a))
            goto err;
    }
    ret = 1;

 err:
    if (ctx != NULL)
        BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_point_init(EC_POINT *point)
{
    BN_init(&point->X);
    BN_init(&point->Y);
    BN_init(&point->Z);
    point->Z_is_one = 0;

    return 1;
}

void ec_GFp_simple_point_finish(EC_POINT *point)
{
    BN_free(&point->X);
    BN_free(&point->Y);
    BN_free(&point->Z);
}

void ec_GFp_simple_point_clear_finish(EC_POINT *point)
{
    BN_clear_free(&point->X);
    BN_clear_free(&point->Y);
    BN_clear_free(&point->Z);
    point->Z_is_one = 0;
}

int ec_GFp_simple_point_copy(EC_POINT *dest, const EC_POINT *src)
{
    if (!BN_copy(&dest->X, &src->X))
        return 0;
    if (!BN_copy(&dest->Y, &src->Y))
        return 0;
    if (!BN_copy(&dest->Z, &src->Z))
        return 0;
    dest->Z_is_one = src->Z_is_one;

    return 1;
}

int ec_GFp_simple_point_set_to_infinity(const EC_GROUP *group,
                                        EC_POINT *point)
{
    point->Z_is_one = 0;
    BN_zero(&point->Z);
    return 1;
}

int ec_GFp_simple_set_Jprojective_coordinates_GFp(const EC_GROUP *group,
                                                  EC_POINT *point,
                                                  const BIGNUM *x,
                                                  const BIGNUM *y,
                                                  const BIGNUM *z,
                                                  BN_CTX *ctx)
{
    BN_CTX *new_ctx = NULL;
    int ret = 0;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    if (x != NULL) {
        if (!BN_nnmod(&point->X, x, &group->field, ctx))
            goto err;
        if (group->meth->field_encode) {
            if (!group->meth->field_encode(group, &point->X, &point->X, ctx))
                goto err;
        }
    }

    if (y != NULL) {
        if (!BN_nnmod(&point->Y, y, &group->field, ctx))
            goto err;
        if (group->meth->field_encode) {
            if (!group->meth->field_encode(group, &point->Y, &point->Y, ctx))
                goto err;
        }
    }

    if (z != NULL) {
        int Z_is_one;

        if (!BN_nnmod(&point->Z, z, &group->field, ctx))
            goto err;
        Z_is_one = BN_is_one(&point->Z);
        if (group->meth->field_encode) {
            if (Z_is_one && (group->meth->field_set_to_one != 0)) {
                if (!group->meth->field_set_to_one(group, &point->Z, ctx))
                    goto err;
            } else {
                if (!group->
                    meth->field_encode(group, &point->Z, &point->Z, ctx))
                    goto err;
            }
        }
        point->Z_is_one = Z_is_one;
    }

    ret = 1;

 err:
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_get_Jprojective_coordinates_GFp(const EC_GROUP *group,
                                                  const EC_POINT *point,
                                                  BIGNUM *x, BIGNUM *y,
                                                  BIGNUM *z, BN_CTX *ctx)
{
    BN_CTX *new_ctx = NULL;
    int ret = 0;

    if (group->meth->field_decode != 0) {
        if (ctx == NULL) {
            ctx = new_ctx = BN_CTX_new();
            if (ctx == NULL)
                return 0;
        }

        if (x != NULL) {
            if (!group->meth->field_decode(group, x, &point->X, ctx))
                goto err;
        }
        if (y != NULL) {
            if (!group->meth->field_decode(group, y, &point->Y, ctx))
                goto err;
        }
        if (z != NULL) {
            if (!group->meth->field_decode(group, z, &point->Z, ctx))
                goto err;
        }
    } else {
        if (x != NULL) {
            if (!BN_copy(x, &point->X))
                goto err;
        }
        if (y != NULL) {
            if (!BN_copy(y, &point->Y))
                goto err;
        }
        if (z != NULL) {
            if (!BN_copy(z, &point->Z))
                goto err;
        }
    }

    ret = 1;

 err:
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_point_set_affine_coordinates(const EC_GROUP *group,
                                               EC_POINT *point,
                                               const BIGNUM *x,
                                               const BIGNUM *y, BN_CTX *ctx)
{
    if (x == NULL || y == NULL) {
        /*
         * unlike for projective coordinates, we do not tolerate this
         */
        ECerr(EC_F_EC_GFP_SIMPLE_POINT_SET_AFFINE_COORDINATES,
              ERR_R_PASSED_NULL_PARAMETER);
        return 0;
    }

    return EC_POINT_set_Jprojective_coordinates_GFp(group, point, x, y,
                                                    BN_value_one(), ctx);
}

int ec_GFp_simple_point_get_affine_coordinates(const EC_GROUP *group,
                                               const EC_POINT *point,
                                               BIGNUM *x, BIGNUM *y,
                                               BN_CTX *ctx)
{
    BN_CTX *new_ctx = NULL;
    BIGNUM *Z, *Z_1, *Z_2, *Z_3;
    const BIGNUM *Z_;
    int ret = 0;

    if (EC_POINT_is_at_infinity(group, point)) {
        ECerr(EC_F_EC_GFP_SIMPLE_POINT_GET_AFFINE_COORDINATES,
              EC_R_POINT_AT_INFINITY);
        return 0;
    }

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    BN_CTX_start(ctx);
    Z = BN_CTX_get(ctx);
    Z_1 = BN_CTX_get(ctx);
    Z_2 = BN_CTX_get(ctx);
    Z_3 = BN_CTX_get(ctx);
    if (Z_3 == NULL)
        goto err;

    /* transform  (X, Y, Z)  into  (x, y) := (X/Z^2, Y/Z^3) */

    if (group->meth->field_decode) {
        if (!group->meth->field_decode(group, Z, &point->Z, ctx))
            goto err;
        Z_ = Z;
    } else {
        Z_ = &point->Z;
    }

    if (BN_is_one(Z_)) {
        if (group->meth->field_decode) {
            if (x != NULL) {
                if (!group->meth->field_decode(group, x, &point->X, ctx))
                    goto err;
            }
            if (y != NULL) {
                if (!group->meth->field_decode(group, y, &point->Y, ctx))
                    goto err;
            }
        } else {
            if (x != NULL) {
                if (!BN_copy(x, &point->X))
                    goto err;
            }
            if (y != NULL) {
                if (!BN_copy(y, &point->Y))
                    goto err;
            }
        }
    } else {
        if (!BN_mod_inverse(Z_1, Z_, &group->field, ctx)) {
            ECerr(EC_F_EC_GFP_SIMPLE_POINT_GET_AFFINE_COORDINATES,
                  ERR_R_BN_LIB);
            goto err;
        }

        if (group->meth->field_encode == 0) {
            /* field_sqr works on standard representation */
            if (!group->meth->field_sqr(group, Z_2, Z_1, ctx))
                goto err;
        } else {
            if (!BN_mod_sqr(Z_2, Z_1, &group->field, ctx))
                goto err;
        }

        if (x != NULL) {
            /*
             * in the Montgomery case, field_mul will cancel out Montgomery
             * factor in X:
             */
            if (!group->meth->field_mul(group, x, &point->X, Z_2, ctx))
                goto err;
        }

        if (y != NULL) {
            if (group->meth->field_encode == 0) {
                /*
                 * field_mul works on standard representation
                 */
                if (!group->meth->field_mul(group, Z_3, Z_2, Z_1, ctx))
                    goto err;
            } else {
                if (!BN_mod_mul(Z_3, Z_2, Z_1, &group->field, ctx))
                    goto err;
            }

            /*
             * in the Montgomery case, field_mul will cancel out Montgomery
             * factor in Y:
             */
            if (!group->meth->field_mul(group, y, &point->Y, Z_3, ctx))
                goto err;
        }
    }

    ret = 1;

 err:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
                                             EC_POINT *point,
                                             const BIGNUM *x_, int y_bit,
                                             BN_CTX *ctx)
{
    BN_CTX *new_ctx = NULL;
    BIGNUM *tmp1, *tmp2, *x, *y;
    int ret = 0;

    /* clear error queue */
    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);
    tmp1 = BN_CTX_get(ctx);
    tmp2 = BN_CTX_get(ctx);
    x = BN_CTX_get(ctx);
    y = BN_CTX_get(ctx);
    if (y == NULL)
        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_nnmod(x, x_, &group->field, ctx))
        goto err;
    if (group->meth->field_decode == 0) {
        /* field_{sqr,mul} work on standard representation */
        if (!group->meth->field_sqr(group, tmp2, x_, ctx))
            goto err;
        if (!group->meth->field_mul(group, tmp1, tmp2, x_, ctx))
            goto err;
    } else {
        if (!BN_mod_sqr(tmp2, x_, &group->field, ctx))
            goto err;
        if (!BN_mod_mul(tmp1, tmp2, x_, &group->field, ctx))
            goto err;
    }

    /* tmp1 := tmp1 + a*x */
    if (group->a_is_minus3) {
        if (!BN_mod_lshift1_quick(tmp2, x, &group->field))
            goto err;
        if (!BN_mod_add_quick(tmp2, tmp2, x, &group->field))
            goto err;
        if (!BN_mod_sub_quick(tmp1, tmp1, tmp2, &group->field))
            goto err;
    } else {
        if (group->meth->field_decode) {
            if (!group->meth->field_decode(group, tmp2, &group->a, ctx))
                goto err;
            if (!BN_mod_mul(tmp2, tmp2, x, &group->field, ctx))
                goto err;
        } else {
            /* field_mul works on standard representation */
            if (!group->meth->field_mul(group, tmp2, &group->a, x, ctx))
                goto err;
        }

        if (!BN_mod_add_quick(tmp1, tmp1, tmp2, &group->field))
            goto err;
    }

    /* tmp1 := tmp1 + b */
    if (group->meth->field_decode) {
        if (!group->meth->field_decode(group, tmp2, &group->b, ctx))
            goto err;
        if (!BN_mod_add_quick(tmp1, tmp1, tmp2, &group->field))
            goto err;
    } else {
        if (!BN_mod_add_quick(tmp1, tmp1, &group->b, &group->field))
            goto err;
    }

    if (!BN_mod_sqrt(y, tmp1, &group->field, ctx)) {
        unsigned long 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();
            ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
                  EC_R_INVALID_COMPRESSED_POINT);
        } else
            ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
                  ERR_R_BN_LIB);
        goto err;
    }

    if (y_bit != BN_is_odd(y)) {
        if (BN_is_zero(y)) {
            int kron;

            kron = BN_kronecker(x, &group->field, ctx);
            if (kron == -2)
                goto err;

            if (kron == 1)
                ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
                      EC_R_INVALID_COMPRESSION_BIT);
            else
                /*
                 * BN_mod_sqrt() should have cought this error (not a square)
                 */
                ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
                      EC_R_INVALID_COMPRESSED_POINT);
            goto err;
        }
        if (!BN_usub(y, &group->field, y))
            goto err;
    }
    if (y_bit != BN_is_odd(y)) {
        ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
              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);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

size_t ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
                               point_conversion_form_t form,
                               unsigned char *buf, size_t len, BN_CTX *ctx)
{
    size_t ret;
    BN_CTX *new_ctx = NULL;
    int used_ctx = 0;
    BIGNUM *x, *y;
    size_t field_len, i, skip;

    if ((form != POINT_CONVERSION_COMPRESSED)
        && (form != POINT_CONVERSION_UNCOMPRESSED)
        && (form != POINT_CONVERSION_HYBRID)) {
        ECerr(EC_F_EC_GFP_SIMPLE_POINT2OCT, EC_R_INVALID_FORM);
        goto err;
    }

    if (EC_POINT_is_at_infinity(group, point)) {
        /* encodes to a single 0 octet */
        if (buf != NULL) {
            if (len < 1) {
                ECerr(EC_F_EC_GFP_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
                return 0;
            }
            buf[0] = 0;
        }
        return 1;
    }

    /* ret := required output buffer length */
    field_len = BN_num_bytes(&group->field);
    ret =
        (form ==
         POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;

    /* if 'buf' is NULL, just return required length */
    if (buf != NULL) {
        if (len < ret) {
            ECerr(EC_F_EC_GFP_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
            goto err;
        }

        if (ctx == NULL) {
            ctx = new_ctx = BN_CTX_new();
            if (ctx == NULL)
                return 0;
        }

        BN_CTX_start(ctx);
        used_ctx = 1;
        x = BN_CTX_get(ctx);
        y = BN_CTX_get(ctx);
        if (y == NULL)
            goto err;

        if (!EC_POINT_get_affine_coordinates_GFp(group, point, x, y, ctx))
            goto err;

        if ((form == POINT_CONVERSION_COMPRESSED
             || form == POINT_CONVERSION_HYBRID) && BN_is_odd(y))
            buf[0] = form + 1;
        else
            buf[0] = form;

        i = 1;

        skip = field_len - BN_num_bytes(x);
        if (skip > field_len) {
            ECerr(EC_F_EC_GFP_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
            goto err;
        }
        while (skip > 0) {
            buf[i++] = 0;
            skip--;
        }
        skip = BN_bn2bin(x, buf + i);
        i += skip;
        if (i != 1 + field_len) {
            ECerr(EC_F_EC_GFP_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
            goto err;
        }

        if (form == POINT_CONVERSION_UNCOMPRESSED
            || form == POINT_CONVERSION_HYBRID) {
            skip = field_len - BN_num_bytes(y);
            if (skip > field_len) {
                ECerr(EC_F_EC_GFP_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
                goto err;
            }
            while (skip > 0) {
                buf[i++] = 0;
                skip--;
            }
            skip = BN_bn2bin(y, buf + i);
            i += skip;
        }

        if (i != ret) {
            ECerr(EC_F_EC_GFP_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
            goto err;
        }
    }

    if (used_ctx)
        BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;

 err:
    if (used_ctx)
        BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return 0;
}

int ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
                            const unsigned char *buf, size_t len, BN_CTX *ctx)
{
    point_conversion_form_t form;
    int y_bit;
    BN_CTX *new_ctx = NULL;
    BIGNUM *x, *y;
    size_t field_len, enc_len;
    int ret = 0;

    if (len == 0) {
        ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
        return 0;
    }
    form = buf[0];
    y_bit = form & 1;
    form = form & ~1U;
    if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
        && (form != POINT_CONVERSION_UNCOMPRESSED)
        && (form != POINT_CONVERSION_HYBRID)) {
        ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
        return 0;
    }
    if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
        ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
        return 0;
    }

    if (form == 0) {
        if (len != 1) {
            ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
            return 0;
        }

        return EC_POINT_set_to_infinity(group, point);
    }

    field_len = BN_num_bytes(&group->field);
    enc_len =
        (form ==
         POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;

    if (len != enc_len) {
        ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
        return 0;
    }

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    BN_CTX_start(ctx);
    x = BN_CTX_get(ctx);
    y = BN_CTX_get(ctx);
    if (y == NULL)
        goto err;

    if (!BN_bin2bn(buf + 1, field_len, x))
        goto err;
    if (BN_ucmp(x, &group->field) >= 0) {
        ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
        goto err;
    }

    if (form == POINT_CONVERSION_COMPRESSED) {
        if (!EC_POINT_set_compressed_coordinates_GFp
            (group, point, x, y_bit, ctx))
            goto err;
    } else {
        if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
            goto err;
        if (BN_ucmp(y, &group->field) >= 0) {
            ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
            goto err;
        }
        if (form == POINT_CONVERSION_HYBRID) {
            if (y_bit != BN_is_odd(y)) {
                ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
                goto err;
            }
        }

        if (!EC_POINT_set_affine_coordinates_GFp(group, point, x, y, ctx))
            goto err;
    }

    /* test required by X9.62 */
    if (!EC_POINT_is_on_curve(group, point, ctx)) {
        ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_POINT_IS_NOT_ON_CURVE);
        goto err;
    }

    ret = 1;

 err:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_add(const EC_GROUP *group, EC_POINT *r, const EC_POINT *a,
                      const EC_POINT *b, BN_CTX *ctx)
{
    int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,
                      const BIGNUM *, BN_CTX *);
    int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
    const BIGNUM *p;
    BN_CTX *new_ctx = NULL;
    BIGNUM *n0, *n1, *n2, *n3, *n4, *n5, *n6;
    int ret = 0;

    if (a == b)
        return EC_POINT_dbl(group, r, a, ctx);
    if (EC_POINT_is_at_infinity(group, a))
        return EC_POINT_copy(r, b);
    if (EC_POINT_is_at_infinity(group, b))
        return EC_POINT_copy(r, a);

    field_mul = group->meth->field_mul;
    field_sqr = group->meth->field_sqr;
    p = &group->field;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    BN_CTX_start(ctx);
    n0 = BN_CTX_get(ctx);
    n1 = BN_CTX_get(ctx);
    n2 = BN_CTX_get(ctx);
    n3 = BN_CTX_get(ctx);
    n4 = BN_CTX_get(ctx);
    n5 = BN_CTX_get(ctx);
    n6 = BN_CTX_get(ctx);
    if (n6 == NULL)
        goto end;

    /*
     * Note that in this function we must not read components of 'a' or 'b'
     * once we have written the corresponding components of 'r'. ('r' might
     * be one of 'a' or 'b'.)
     */

    /* n1, n2 */
    if (b->Z_is_one) {
        if (!BN_copy(n1, &a->X))
            goto end;
        if (!BN_copy(n2, &a->Y))
            goto end;
        /* n1 = X_a */
        /* n2 = Y_a */
    } else {
        if (!field_sqr(group, n0, &b->Z, ctx))
            goto end;
        if (!field_mul(group, n1, &a->X, n0, ctx))
            goto end;
        /* n1 = X_a * Z_b^2 */

        if (!field_mul(group, n0, n0, &b->Z, ctx))
            goto end;
        if (!field_mul(group, n2, &a->Y, n0, ctx))
            goto end;
        /* n2 = Y_a * Z_b^3 */
    }

    /* n3, n4 */
    if (a->Z_is_one) {
        if (!BN_copy(n3, &b->X))
            goto end;
        if (!BN_copy(n4, &b->Y))
            goto end;
        /* n3 = X_b */
        /* n4 = Y_b */
    } else {
        if (!field_sqr(group, n0, &a->Z, ctx))
            goto end;
        if (!field_mul(group, n3, &b->X, n0, ctx))
            goto end;
        /* n3 = X_b * Z_a^2 */

        if (!field_mul(group, n0, n0, &a->Z, ctx))
            goto end;
        if (!field_mul(group, n4, &b->Y, n0, ctx))
            goto end;
        /* n4 = Y_b * Z_a^3 */
    }

    /* n5, n6 */
    if (!BN_mod_sub_quick(n5, n1, n3, p))
        goto end;
    if (!BN_mod_sub_quick(n6, n2, n4, p))
        goto end;
    /* n5 = n1 - n3 */
    /* n6 = n2 - n4 */

    if (BN_is_zero(n5)) {
        if (BN_is_zero(n6)) {
            /* a is the same point as b */
            BN_CTX_end(ctx);
            ret = EC_POINT_dbl(group, r, a, ctx);
            ctx = NULL;
            goto end;
        } else {
            /* a is the inverse of b */
            BN_zero(&r->Z);
            r->Z_is_one = 0;
            ret = 1;
            goto end;
        }
    }

    /* 'n7', 'n8' */
    if (!BN_mod_add_quick(n1, n1, n3, p))
        goto end;
    if (!BN_mod_add_quick(n2, n2, n4, p))
        goto end;
    /* 'n7' = n1 + n3 */
    /* 'n8' = n2 + n4 */

    /* Z_r */
    if (a->Z_is_one && b->Z_is_one) {
        if (!BN_copy(&r->Z, n5))
            goto end;
    } else {
        if (a->Z_is_one) {
            if (!BN_copy(n0, &b->Z))
                goto end;
        } else if (b->Z_is_one) {
            if (!BN_copy(n0, &a->Z))
                goto end;
        } else {
            if (!field_mul(group, n0, &a->Z, &b->Z, ctx))
                goto end;
        }
        if (!field_mul(group, &r->Z, n0, n5, ctx))
            goto end;
    }
    r->Z_is_one = 0;
    /* Z_r = Z_a * Z_b * n5 */

    /* X_r */
    if (!field_sqr(group, n0, n6, ctx))
        goto end;
    if (!field_sqr(group, n4, n5, ctx))
        goto end;
    if (!field_mul(group, n3, n1, n4, ctx))
        goto end;
    if (!BN_mod_sub_quick(&r->X, n0, n3, p))
        goto end;
    /* X_r = n6^2 - n5^2 * 'n7' */

    /* 'n9' */
    if (!BN_mod_lshift1_quick(n0, &r->X, p))
        goto end;
    if (!BN_mod_sub_quick(n0, n3, n0, p))
        goto end;
    /* n9 = n5^2 * 'n7' - 2 * X_r */

    /* Y_r */
    if (!field_mul(group, n0, n0, n6, ctx))
        goto end;
    if (!field_mul(group, n5, n4, n5, ctx))
        goto end;               /* now n5 is n5^3 */
    if (!field_mul(group, n1, n2, n5, ctx))
        goto end;
    if (!BN_mod_sub_quick(n0, n0, n1, p))
        goto end;
    if (BN_is_odd(n0))
        if (!BN_add(n0, n0, p))
            goto end;
    /* now  0 <= n0 < 2*p,  and n0 is even */
    if (!BN_rshift1(&r->Y, n0))
        goto end;
    /* Y_r = (n6 * 'n9' - 'n8' * 'n5^3') / 2 */

    ret = 1;

 end:
    if (ctx)                    /* otherwise we already called BN_CTX_end */
        BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_dbl(const EC_GROUP *group, EC_POINT *r, const EC_POINT *a,
                      BN_CTX *ctx)
{
    int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,
                      const BIGNUM *, BN_CTX *);
    int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
    const BIGNUM *p;
    BN_CTX *new_ctx = NULL;
    BIGNUM *n0, *n1, *n2, *n3;
    int ret = 0;

    if (EC_POINT_is_at_infinity(group, a)) {
        BN_zero(&r->Z);
        r->Z_is_one = 0;
        return 1;
    }

    field_mul = group->meth->field_mul;
    field_sqr = group->meth->field_sqr;
    p = &group->field;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    BN_CTX_start(ctx);
    n0 = BN_CTX_get(ctx);
    n1 = BN_CTX_get(ctx);
    n2 = BN_CTX_get(ctx);
    n3 = BN_CTX_get(ctx);
    if (n3 == NULL)
        goto err;

    /*
     * Note that in this function we must not read components of 'a' once we
     * have written the corresponding components of 'r'. ('r' might the same
     * as 'a'.)
     */

    /* n1 */
    if (a->Z_is_one) {
        if (!field_sqr(group, n0, &a->X, ctx))
            goto err;
        if (!BN_mod_lshift1_quick(n1, n0, p))
            goto err;
        if (!BN_mod_add_quick(n0, n0, n1, p))
            goto err;
        if (!BN_mod_add_quick(n1, n0, &group->a, p))
            goto err;
        /* n1 = 3 * X_a^2 + a_curve */
    } else if (group->a_is_minus3) {
        if (!field_sqr(group, n1, &a->Z, ctx))
            goto err;
        if (!BN_mod_add_quick(n0, &a->X, n1, p))
            goto err;
        if (!BN_mod_sub_quick(n2, &a->X, n1, p))
            goto err;
        if (!field_mul(group, n1, n0, n2, ctx))
            goto err;
        if (!BN_mod_lshift1_quick(n0, n1, p))
            goto err;
        if (!BN_mod_add_quick(n1, n0, n1, p))
            goto err;
        /*-
         * n1 = 3 * (X_a + Z_a^2) * (X_a - Z_a^2)
         *    = 3 * X_a^2 - 3 * Z_a^4
         */
    } else {
        if (!field_sqr(group, n0, &a->X, ctx))
            goto err;
        if (!BN_mod_lshift1_quick(n1, n0, p))
            goto err;
        if (!BN_mod_add_quick(n0, n0, n1, p))
            goto err;
        if (!field_sqr(group, n1, &a->Z, ctx))
            goto err;
        if (!field_sqr(group, n1, n1, ctx))
            goto err;
        if (!field_mul(group, n1, n1, &group->a, ctx))
            goto err;
        if (!BN_mod_add_quick(n1, n1, n0, p))
            goto err;
        /* n1 = 3 * X_a^2 + a_curve * Z_a^4 */
    }

    /* Z_r */
    if (a->Z_is_one) {
        if (!BN_copy(n0, &a->Y))
            goto err;
    } else {
        if (!field_mul(group, n0, &a->Y, &a->Z, ctx))
            goto err;
    }
    if (!BN_mod_lshift1_quick(&r->Z, n0, p))
        goto err;
    r->Z_is_one = 0;
    /* Z_r = 2 * Y_a * Z_a */

    /* n2 */
    if (!field_sqr(group, n3, &a->Y, ctx))
        goto err;
    if (!field_mul(group, n2, &a->X, n3, ctx))
        goto err;
    if (!BN_mod_lshift_quick(n2, n2, 2, p))
        goto err;
    /* n2 = 4 * X_a * Y_a^2 */

    /* X_r */
    if (!BN_mod_lshift1_quick(n0, n2, p))
        goto err;
    if (!field_sqr(group, &r->X, n1, ctx))
        goto err;
    if (!BN_mod_sub_quick(&r->X, &r->X, n0, p))
        goto err;
    /* X_r = n1^2 - 2 * n2 */

    /* n3 */
    if (!field_sqr(group, n0, n3, ctx))
        goto err;
    if (!BN_mod_lshift_quick(n3, n0, 3, p))
        goto err;
    /* n3 = 8 * Y_a^4 */

    /* Y_r */
    if (!BN_mod_sub_quick(n0, n2, &r->X, p))
        goto err;
    if (!field_mul(group, n0, n1, n0, ctx))
        goto err;
    if (!BN_mod_sub_quick(&r->Y, n0, n3, p))
        goto err;
    /* Y_r = n1 * (n2 - X_r) - n3 */

    ret = 1;

 err:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_invert(const EC_GROUP *group, EC_POINT *point, BN_CTX *ctx)
{
    if (EC_POINT_is_at_infinity(group, point) || BN_is_zero(&point->Y))
        /* point is its own inverse */
        return 1;

    return BN_usub(&point->Y, &group->field, &point->Y);
}

int ec_GFp_simple_is_at_infinity(const EC_GROUP *group, const EC_POINT *point)
{
    return BN_is_zero(&point->Z);
}

int ec_GFp_simple_is_on_curve(const EC_GROUP *group, const EC_POINT *point,
                              BN_CTX *ctx)
{
    int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,
                      const BIGNUM *, BN_CTX *);
    int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
    const BIGNUM *p;
    BN_CTX *new_ctx = NULL;
    BIGNUM *rh, *tmp, *Z4, *Z6;
    int ret = -1;

    if (EC_POINT_is_at_infinity(group, point))
        return 1;

    field_mul = group->meth->field_mul;
    field_sqr = group->meth->field_sqr;
    p = &group->field;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return -1;
    }

    BN_CTX_start(ctx);
    rh = BN_CTX_get(ctx);
    tmp = BN_CTX_get(ctx);
    Z4 = BN_CTX_get(ctx);
    Z6 = BN_CTX_get(ctx);
    if (Z6 == NULL)
        goto err;

    /*-
     * We have a curve defined by a Weierstrass equation
     *      y^2 = x^3 + a*x + b.
     * The point to consider is given in Jacobian projective coordinates
     * where  (X, Y, Z)  represents  (x, y) = (X/Z^2, Y/Z^3).
     * Substituting this and multiplying by  Z^6  transforms the above equation into
     *      Y^2 = X^3 + a*X*Z^4 + b*Z^6.
     * To test this, we add up the right-hand side in 'rh'.
     */

    /* rh := X^2 */
    if (!field_sqr(group, rh, &point->X, ctx))
        goto err;

    if (!point->Z_is_one) {
        if (!field_sqr(group, tmp, &point->Z, ctx))
            goto err;
        if (!field_sqr(group, Z4, tmp, ctx))
            goto err;
        if (!field_mul(group, Z6, Z4, tmp, ctx))
            goto err;

        /* rh := (rh + a*Z^4)*X */
        if (group->a_is_minus3) {
            if (!BN_mod_lshift1_quick(tmp, Z4, p))
                goto err;
            if (!BN_mod_add_quick(tmp, tmp, Z4, p))
                goto err;
            if (!BN_mod_sub_quick(rh, rh, tmp, p))
                goto err;
            if (!field_mul(group, rh, rh, &point->X, ctx))
                goto err;
        } else {
            if (!field_mul(group, tmp, Z4, &group->a, ctx))
                goto err;
            if (!BN_mod_add_quick(rh, rh, tmp, p))
                goto err;
            if (!field_mul(group, rh, rh, &point->X, ctx))
                goto err;
        }

        /* rh := rh + b*Z^6 */
        if (!field_mul(group, tmp, &group->b, Z6, ctx))
            goto err;
        if (!BN_mod_add_quick(rh, rh, tmp, p))
            goto err;
    } else {
        /* point->Z_is_one */

        /* rh := (rh + a)*X */
        if (!BN_mod_add_quick(rh, rh, &group->a, p))
            goto err;
        if (!field_mul(group, rh, rh, &point->X, ctx))
            goto err;
        /* rh := rh + b */
        if (!BN_mod_add_quick(rh, rh, &group->b, p))
            goto err;
    }

    /* 'lh' := Y^2 */
    if (!field_sqr(group, tmp, &point->Y, ctx))
        goto err;

    ret = (0 == BN_ucmp(tmp, rh));

 err:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_cmp(const EC_GROUP *group, const EC_POINT *a,
                      const EC_POINT *b, BN_CTX *ctx)
{
    /*-
     * return values:
     *  -1   error
     *   0   equal (in affine coordinates)
     *   1   not equal
     */

    int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,
                      const BIGNUM *, BN_CTX *);
    int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
    BN_CTX *new_ctx = NULL;
    BIGNUM *tmp1, *tmp2, *Za23, *Zb23;
    const BIGNUM *tmp1_, *tmp2_;
    int ret = -1;

    if (EC_POINT_is_at_infinity(group, a)) {
        return EC_POINT_is_at_infinity(group, b) ? 0 : 1;
    }

    if (EC_POINT_is_at_infinity(group, b))
        return 1;

    if (a->Z_is_one && b->Z_is_one) {
        return ((BN_cmp(&a->X, &b->X) == 0)
                && BN_cmp(&a->Y, &b->Y) == 0) ? 0 : 1;
    }

    field_mul = group->meth->field_mul;
    field_sqr = group->meth->field_sqr;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return -1;
    }

    BN_CTX_start(ctx);
    tmp1 = BN_CTX_get(ctx);
    tmp2 = BN_CTX_get(ctx);
    Za23 = BN_CTX_get(ctx);
    Zb23 = BN_CTX_get(ctx);
    if (Zb23 == NULL)
        goto end;

    /*-
     * We have to decide whether
     *     (X_a/Z_a^2, Y_a/Z_a^3) = (X_b/Z_b^2, Y_b/Z_b^3),
     * or equivalently, whether
     *     (X_a*Z_b^2, Y_a*Z_b^3) = (X_b*Z_a^2, Y_b*Z_a^3).
     */

    if (!b->Z_is_one) {
        if (!field_sqr(group, Zb23, &b->Z, ctx))
            goto end;
        if (!field_mul(group, tmp1, &a->X, Zb23, ctx))
            goto end;
        tmp1_ = tmp1;
    } else
        tmp1_ = &a->X;
    if (!a->Z_is_one) {
        if (!field_sqr(group, Za23, &a->Z, ctx))
            goto end;
        if (!field_mul(group, tmp2, &b->X, Za23, ctx))
            goto end;
        tmp2_ = tmp2;
    } else
        tmp2_ = &b->X;

    /* compare  X_a*Z_b^2  with  X_b*Z_a^2 */
    if (BN_cmp(tmp1_, tmp2_) != 0) {
        ret = 1;                /* points differ */
        goto end;
    }

    if (!b->Z_is_one) {
        if (!field_mul(group, Zb23, Zb23, &b->Z, ctx))
            goto end;
        if (!field_mul(group, tmp1, &a->Y, Zb23, ctx))
            goto end;
        /* tmp1_ = tmp1 */
    } else
        tmp1_ = &a->Y;
    if (!a->Z_is_one) {
        if (!field_mul(group, Za23, Za23, &a->Z, ctx))
            goto end;
        if (!field_mul(group, tmp2, &b->Y, Za23, ctx))
            goto end;
        /* tmp2_ = tmp2 */
    } else
        tmp2_ = &b->Y;

    /* compare  Y_a*Z_b^3  with  Y_b*Z_a^3 */
    if (BN_cmp(tmp1_, tmp2_) != 0) {
        ret = 1;                /* points differ */
        goto end;
    }

    /* points are equal */
    ret = 0;

 end:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_make_affine(const EC_GROUP *group, EC_POINT *point,
                              BN_CTX *ctx)
{
    BN_CTX *new_ctx = NULL;
    BIGNUM *x, *y;
    int ret = 0;

    if (point->Z_is_one || EC_POINT_is_at_infinity(group, point))
        return 1;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    BN_CTX_start(ctx);
    x = BN_CTX_get(ctx);
    y = BN_CTX_get(ctx);
    if (y == NULL)
        goto err;

    if (!EC_POINT_get_affine_coordinates_GFp(group, point, x, y, ctx))
        goto err;
    if (!EC_POINT_set_affine_coordinates_GFp(group, point, x, y, ctx))
        goto err;
    if (!point->Z_is_one) {
        ECerr(EC_F_EC_GFP_SIMPLE_MAKE_AFFINE, ERR_R_INTERNAL_ERROR);
        goto err;
    }

    ret = 1;

 err:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    return ret;
}

int ec_GFp_simple_points_make_affine(const EC_GROUP *group, size_t num,
                                     EC_POINT *points[], BN_CTX *ctx)
{
    BN_CTX *new_ctx = NULL;
    BIGNUM *tmp, *tmp_Z;
    BIGNUM **prod_Z = NULL;
    size_t i;
    int ret = 0;

    if (num == 0)
        return 1;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new();
        if (ctx == NULL)
            return 0;
    }

    BN_CTX_start(ctx);
    tmp = BN_CTX_get(ctx);
    tmp_Z = BN_CTX_get(ctx);
    if (tmp == NULL || tmp_Z == NULL)
        goto err;

    prod_Z = OPENSSL_malloc(num * sizeof prod_Z[0]);
    if (prod_Z == NULL)
        goto err;
    for (i = 0; i < num; i++) {
        prod_Z[i] = BN_new();
        if (prod_Z[i] == NULL)
            goto err;
    }

    /*
     * Set each prod_Z[i] to the product of points[0]->Z .. points[i]->Z,
     * skipping any zero-valued inputs (pretend that they're 1).
     */

    if (!BN_is_zero(&points[0]->Z)) {
        if (!BN_copy(prod_Z[0], &points[0]->Z))
            goto err;
    } else {
        if (group->meth->field_set_to_one != 0) {
            if (!group->meth->field_set_to_one(group, prod_Z[0], ctx))
                goto err;
        } else {
            if (!BN_one(prod_Z[0]))
                goto err;
        }
    }

    for (i = 1; i < num; i++) {
        if (!BN_is_zero(&points[i]->Z)) {
            if (!group->meth->field_mul(group, prod_Z[i], prod_Z[i - 1],
                                        &points[i]->Z, ctx))
                goto err;
        } else {
            if (!BN_copy(prod_Z[i], prod_Z[i - 1]))
                goto err;
        }
    }

    /*
     * Now use a single explicit inversion to replace every non-zero
     * points[i]->Z by its inverse.
     */

    if (!BN_mod_inverse(tmp, prod_Z[num - 1], &group->field, ctx)) {
        ECerr(EC_F_EC_GFP_SIMPLE_POINTS_MAKE_AFFINE, ERR_R_BN_LIB);
        goto err;
    }
    if (group->meth->field_encode != 0) {
        /*
         * In the Montgomery case, we just turned R*H (representing H) into
         * 1/(R*H), but we need R*(1/H) (representing 1/H); i.e. we need to
         * multiply by the Montgomery factor twice.
         */
        if (!group->meth->field_encode(group, tmp, tmp, ctx))
            goto err;
        if (!group->meth->field_encode(group, tmp, tmp, ctx))
            goto err;
    }

    for (i = num - 1; i > 0; --i) {
        /*
         * Loop invariant: tmp is the product of the inverses of points[0]->Z
         * .. points[i]->Z (zero-valued inputs skipped).
         */
        if (!BN_is_zero(&points[i]->Z)) {
            /*
             * Set tmp_Z to the inverse of points[i]->Z (as product of Z
             * inverses 0 .. i, Z values 0 .. i - 1).
             */
            if (!group->
                meth->field_mul(group, tmp_Z, prod_Z[i - 1], tmp, ctx))
                goto err;
            /*
             * Update tmp to satisfy the loop invariant for i - 1.
             */
            if (!group->meth->field_mul(group, tmp, tmp, &points[i]->Z, ctx))
                goto err;
            /* Replace points[i]->Z by its inverse. */
            if (!BN_copy(&points[i]->Z, tmp_Z))
                goto err;
        }
    }

    if (!BN_is_zero(&points[0]->Z)) {
        /* Replace points[0]->Z by its inverse. */
        if (!BN_copy(&points[0]->Z, tmp))
            goto err;
    }

    /* Finally, fix up the X and Y coordinates for all points. */

    for (i = 0; i < num; i++) {
        EC_POINT *p = points[i];

        if (!BN_is_zero(&p->Z)) {
            /* turn  (X, Y, 1/Z)  into  (X/Z^2, Y/Z^3, 1) */

            if (!group->meth->field_sqr(group, tmp, &p->Z, ctx))
                goto err;
            if (!group->meth->field_mul(group, &p->X, &p->X, tmp, ctx))
                goto err;

            if (!group->meth->field_mul(group, tmp, tmp, &p->Z, ctx))
                goto err;
            if (!group->meth->field_mul(group, &p->Y, &p->Y, tmp, ctx))
                goto err;

            if (group->meth->field_set_to_one != 0) {
                if (!group->meth->field_set_to_one(group, &p->Z, ctx))
                    goto err;
            } else {
                if (!BN_one(&p->Z))
                    goto err;
            }
            p->Z_is_one = 1;
        }
    }

    ret = 1;

 err:
    BN_CTX_end(ctx);
    if (new_ctx != NULL)
        BN_CTX_free(new_ctx);
    if (prod_Z != NULL) {
        for (i = 0; i < num; i++) {
            if (prod_Z[i] == NULL)
                break;
            BN_clear_free(prod_Z[i]);
        }
        OPENSSL_free(prod_Z);
    }
    return ret;
}

int ec_GFp_simple_field_mul(const EC_GROUP *group, BIGNUM *r, const BIGNUM *a,
                            const BIGNUM *b, BN_CTX *ctx)
{
    return BN_mod_mul(r, a, b, &group->field, ctx);
}

int ec_GFp_simple_field_sqr(const EC_GROUP *group, BIGNUM *r, const BIGNUM *a,
                            BN_CTX *ctx)
{
    return BN_mod_sqr(r, a, &group->field, ctx);
}