/*

 * Copyright 2011-2021 The OpenSSL Project Authors. All Rights Reserved.

 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved

 *

 * Licensed under the OpenSSL license (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

#include <openssl/err.h>

#include "ec_local.h"

#ifndef OPENSSL_NO_EC2M

/*-

 * Calculates and sets the affine coordinates of an EC_POINT from the given

 * compressed coordinates.  Uses algorithm 2.3.4 of SEC 1.

 * Note that the simple implementation only uses affine coordinates.

 *

 * The method is from the following publication:

 *

 *     Harper, Menezes, Vanstone:

 *     "Public-Key Cryptosystems with Very Small Key Lengths",

 *     EUROCRYPT '92, Springer-Verlag LNCS 658,

 *     published February 1993

 *

 * US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe

 * the same method, but claim no priority date earlier than July 29, 1994

 * (and additionally fail to cite the EUROCRYPT '92 publication as prior art).

 */

int ec_GF2m_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 *tmp, *x, *y, *z;

    int ret = 0, z0;

    /* 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) ? 1 : 0;

    BN_CTX_start(ctx);

    tmp = BN_CTX_get(ctx);

    x = BN_CTX_get(ctx);

    y = BN_CTX_get(ctx);

    z = BN_CTX_get(ctx);

    if (z == NULL)

        goto err;

    if (!BN_GF2m_mod_arr(x, x_, group->poly))

        goto err;

    if (BN_is_zero(x)) {

        if (!BN_GF2m_mod_sqrt_arr(y, group->b, group->poly, ctx))

            goto err;

    } else {

        if (!group->meth->field_sqr(group, tmp, x, ctx))

            goto err;

        if (!group->meth->field_div(group, tmp, group->b, tmp, ctx))

            goto err;

        if (!BN_GF2m_add(tmp, group->a, tmp))

            goto err;

        if (!BN_GF2m_add(tmp, x, tmp))

            goto err;

        if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {

            unsigned long err = ERR_peek_last_error();

            if (ERR_GET_LIB(err) == ERR_LIB_BN

                && ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {

                ERR_clear_error();

                ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,

                      EC_R_INVALID_COMPRESSED_POINT);

            } else

                ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,

                      ERR_R_BN_LIB);

            goto err;

        }

        z0 = (BN_is_odd(z)) ? 1 : 0;

        if (!group->meth->field_mul(group, y, x, z, ctx))

            goto err;

        if (z0 != y_bit) {

            if (!BN_GF2m_add(y, y, x))

                goto err;

        }

    }

    if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))

        goto err;

    ret = 1;

 err:

    BN_CTX_end(ctx);

    BN_CTX_free(new_ctx);

    return ret;

}

/*

 * Converts an EC_POINT to an octet string. If buf is NULL, the encoded

 * length will be returned. If the length len of buf is smaller than required

 * an error will be returned.

 */

size_t ec_GF2m_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, *yxi;

    size_t field_len, i, skip;

    if ((form != POINT_CONVERSION_COMPRESSED)

        && (form != POINT_CONVERSION_UNCOMPRESSED)

        && (form != POINT_CONVERSION_HYBRID)) {

        ECerr(EC_F_EC_GF2M_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_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);

                return 0;

            }

            buf[0] = 0;

        }

        return 1;

    }

    /* ret := required output buffer length */

    field_len = (EC_GROUP_get_degree(group) + 7) / 8;

    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_GF2M_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);

        yxi = BN_CTX_get(ctx);

        if (yxi == NULL)

            goto err;

        if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))

            goto err;

        buf[0] = form;

        if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {

            if (!group->meth->field_div(group, yxi, y, x, ctx))

                goto err;

            if (BN_is_odd(yxi))

                buf[0]++;

        }

        i = 1;

        skip = field_len - BN_num_bytes(x);

        if (skip > field_len) {

            ECerr(EC_F_EC_GF2M_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_GF2M_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_GF2M_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_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);

            goto err;

        }

    }

    if (used_ctx)

        BN_CTX_end(ctx);

    BN_CTX_free(new_ctx);

    return ret;

 err:

    if (used_ctx)

        BN_CTX_end(ctx);

    BN_CTX_free(new_ctx);

    return 0;

}

/*

 * Converts an octet string representation to an EC_POINT. Note that the

 * simple implementation only uses affine coordinates.

 */

int ec_GF2m_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, m;

    BN_CTX *new_ctx = NULL;

    BIGNUM *x, *y, *yxi;

    size_t field_len, enc_len;

    int ret = 0;

    if (len == 0) {

        ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);

        return 0;

    }

    /*

     * The first octet is the point converison octet PC, see X9.62, page 4

     * and section 4.4.2.  It must be:

     *     0x00          for the point at infinity

     *     0x02 or 0x03  for compressed form

     *     0x04          for uncompressed form

     *     0x06 or 0x07  for hybrid form.

     * For compressed or hybrid forms, we store the last bit of buf[0] as

     * y_bit and clear it from buf[0] so as to obtain a POINT_CONVERSION_*.

     * We error if buf[0] contains any but the above values.

     */

    y_bit = buf[0] & 1;

    form = buf[0] & ~1U;

    if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)

        && (form != POINT_CONVERSION_UNCOMPRESSED)

        && (form != POINT_CONVERSION_HYBRID)) {

        ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);

        return 0;

    }

    if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {

        ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);

        return 0;

    }

    /* The point at infinity is represented by a single zero octet. */

    if (form == 0) {

        if (len != 1) {

            ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);

            return 0;

        }

        return EC_POINT_set_to_infinity(group, point);

    }

    m = EC_GROUP_get_degree(group);

    field_len = (m + 7) / 8;

    enc_len =

        (form ==

         POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;

    if (len != enc_len) {

        ECerr(EC_F_EC_GF2M_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);

    yxi = BN_CTX_get(ctx);

    if (yxi == NULL)

        goto err;

    if (!BN_bin2bn(buf + 1, field_len, x))

        goto err;

    if (BN_num_bits(x) > m) {

        ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);

        goto err;

    }

    if (form == POINT_CONVERSION_COMPRESSED) {

        if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))

            goto err;

    } else {

        if (!BN_bin2bn(buf + 1 + field_len, field_len, y))

            goto err;

        if (BN_num_bits(y) > m) {

            ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);

            goto err;

        }

        if (form == POINT_CONVERSION_HYBRID) {

            /*

             * Check that the form in the encoding was set correctly

             * according to X9.62 4.4.2.a, 4(c), see also first paragraph

             * of X9.62, 4.4.1.b.

             */

            if (BN_is_zero(x)) {

                if (y_bit != 0) {

                    ECerr(ERR_LIB_EC, EC_R_INVALID_ENCODING);

                    goto err;

                }

            } else {

                if (!group->meth->field_div(group, yxi, y, x, ctx))

                    goto err;

                if (y_bit != BN_is_odd(yxi)) {

                    ECerr(ERR_LIB_EC, EC_R_INVALID_ENCODING);

                    goto err;

                }

            }

        }

        /*

         * EC_POINT_set_affine_coordinates is responsible for checking that

         * the point is on the curve.

         */

        if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))

            goto err;

    }

    ret = 1;

 err:

    BN_CTX_end(ctx);

    BN_CTX_free(new_ctx);

    return ret;

}

#endif