/*
 * Written by Stephen Henson for the OpenSSL project.
 */
/* ====================================================================
 * Copyright (c) 2013 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.
 * ====================================================================
 */

#include <string.h>

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

#include "ech_locl.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;
}