/* $OpenBSD: ecdh.c,v 1.13 2026/03/18 08:02:40 tb Exp $ */
/* ====================================================================
 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
 *
 * The Elliptic Curve Public-Key Crypto Library (ECC Code) included
 * herein is developed by SUN MICROSYSTEMS, INC., and is contributed
 * to the OpenSSL project.
 *
 * The ECC Code is licensed pursuant to the OpenSSL open source
 * license provided below.
 *
 * The ECDH software is originally written by Douglas Stebila of
 * Sun Microsystems Laboratories.
 *
 */
/* ====================================================================
 * Copyright (c) 1998-2003 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).
 *
 */

#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/evp.h>

#include "ec_local.h"
#include "err_local.h"

/*
 * Key derivation function from X9.63/SECG.
 */

/* Way more than we will ever need */
#define ECDH_KDF_MAX    (1 << 30)

int
ecdh_KDF_X9_63(unsigned char *out, size_t outlen, const unsigned char *Z,
    size_t Zlen, const unsigned char *sinfo, size_t sinfolen, const EVP_MD *md)
{
        EVP_MD_CTX *mctx = NULL;
        unsigned int i;
        size_t mdlen;
        unsigned char ctr[4];
        int rv = 0;

        if (sinfolen > ECDH_KDF_MAX || outlen > ECDH_KDF_MAX ||
            Zlen > ECDH_KDF_MAX)
                return 0;
        mctx = EVP_MD_CTX_new();
        if (mctx == NULL)
                return 0;
        mdlen = EVP_MD_size(md);
        for (i = 1;; i++) {
                unsigned char mtmp[EVP_MAX_MD_SIZE];
                if (!EVP_DigestInit_ex(mctx, md, NULL))
                        goto err;
                ctr[3] = i & 0xFF;
                ctr[2] = (i >> 8) & 0xFF;
                ctr[1] = (i >> 16) & 0xFF;
                ctr[0] = (i >> 24) & 0xFF;
                if (!EVP_DigestUpdate(mctx, Z, Zlen))
                        goto err;
                if (!EVP_DigestUpdate(mctx, ctr, sizeof(ctr)))
                        goto err;
                if (!EVP_DigestUpdate(mctx, sinfo, sinfolen))
                        goto err;
                if (outlen >= mdlen) {
                        if (!EVP_DigestFinal(mctx, out, NULL))
                                goto err;
                        outlen -= mdlen;
                        if (outlen == 0)
                                break;
                        out += mdlen;
                } else {
                        if (!EVP_DigestFinal(mctx, mtmp, NULL))
                                goto err;
                        memcpy(out, mtmp, outlen);
                        explicit_bzero(mtmp, mdlen);
                        break;
                }
        }
        rv = 1;

 err:
        EVP_MD_CTX_free(mctx);

        return rv;
}

/*
 * Based on the ECKAS-DH1 and ECSVDP-DH primitives in the IEEE 1363 standard.
 */
int
ec_key_ecdh_compute_key(unsigned char **out, size_t *out_len,
    const EC_POINT *pub_key, const EC_KEY *ecdh)
{
        BN_CTX *ctx;
        BIGNUM *x;
        const BIGNUM *priv_key;
        const EC_GROUP *group;
        EC_POINT *point = NULL;
        unsigned char *buf = NULL;
        int buf_len = 0;
        int ret = 0;

        *out = NULL;
        *out_len = 0;

        if ((ctx = BN_CTX_new()) == NULL)
                goto err;

        BN_CTX_start(ctx);

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

        if ((group = EC_KEY_get0_group(ecdh)) == NULL)
                goto err;

        if (EC_POINT_is_on_curve(group, pub_key, ctx) <= 0)
                goto err;

        if ((point = EC_POINT_new(group)) == NULL) {
                ECerror(ERR_R_MALLOC_FAILURE);
                goto err;
        }

        if ((priv_key = EC_KEY_get0_private_key(ecdh)) == NULL) {
                ECerror(EC_R_MISSING_PRIVATE_KEY);
                goto err;
        }

        if (!EC_POINT_mul(group, point, NULL, pub_key, priv_key, ctx)) {
                ECerror(EC_R_POINT_ARITHMETIC_FAILURE);
                goto err;
        }

        if (!EC_POINT_get_affine_coordinates(group, point, x, NULL, ctx)) {
                ECerror(EC_R_POINT_ARITHMETIC_FAILURE);
                goto err;
        }

        if ((buf_len = ECDH_size(ecdh)) < BN_num_bytes(x)) {
                ECerror(ERR_R_INTERNAL_ERROR);
                goto err;
        }
        if ((buf = calloc(1, buf_len)) == NULL) {
                ECerror(ERR_R_MALLOC_FAILURE);
                goto err;
        }
        if (BN_bn2binpad(x, buf, buf_len) != buf_len) {
                ECerror(ERR_R_BN_LIB);
                goto err;
        }

        *out = buf;
        *out_len = buf_len;
        buf = NULL;
        buf_len = 0;

        ret = 1;

 err:
        EC_POINT_free(point);
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        freezero(buf, buf_len);

        return ret;
}

int
ECDH_compute_key(void *out, size_t out_len, const EC_POINT *pub_key,
    EC_KEY *eckey,
    void *(*KDF)(const void *in, size_t inlen, void *out, size_t *out_len))
{
        unsigned char *secret = NULL;
        size_t secret_len = 0;
        int ret = 0;

        if (eckey->meth->compute_key == NULL) {
                ECerror(EC_R_NOT_IMPLEMENTED);
                goto err;
        }

        if (out_len > INT_MAX) {
                ECerror(EC_R_INVALID_OUTPUT_LENGTH);
                goto err;
        }

        if (!eckey->meth->compute_key(&secret, &secret_len, pub_key, eckey))
                goto err;

        memset(out, 0, out_len);
        if (KDF != NULL) {
                if (KDF(secret, secret_len, out, &out_len) == NULL) {
                        ECerror(EC_R_KDF_FAILED);
                        goto err;
                }
        } else {
                if (out_len < secret_len) {
                        /* The resulting key would be truncated. */
                        ECerror(EC_R_KEY_TRUNCATION);
                        goto err;
                }
                out_len = secret_len;
                memcpy(out, secret, out_len);
        }

        if (out_len > INT_MAX) {
                ECerror(EC_R_INVALID_OUTPUT_LENGTH);
                goto err;
        }

        ret = out_len;

 err:
        freezero(secret, secret_len);

        return ret;
}
LCRYPTO_ALIAS(ECDH_compute_key);

int
ECDH_size(const EC_KEY *eckey)
{
        return BN_num_bytes(eckey->group->p);
}
LCRYPTO_ALIAS(ECDH_size);