Hmac.cpp

/*
 * Copyright (c) 2014-2016 Western Digital Corporation or its affiliates <copyrightagent@wdc.com>
 * @author Gary Ballance <gary.ballance@wdc.com>
 *
 * SPDX-License-Identifier: GPL-2.0+
 * This file is part of Kinetic Advanced Object Store (KAOS).
 *
 * This program is free software: you may copy, redistribute and/or modify it under the terms of the
 * GNU General Public License as published by the Free Software Foundation, either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if
 * not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA. <http://www.gnu.org/licenses/>
 */

/*
 * Include Files
 */
#include <stdint.h>
#include <arpa/inet.h>
#include <openssl/sha.h>
#include <openssl/hmac.h>
#include <string>
#include "Hmac.hpp"

/**
 * Computes a SHA1 HMAC for the specified data using the specified key.  The size of the data can be
 * optionality prepended to the data before hashing.  Currently, HMAC is only generated using SHA1.
 *
 * @param   data            The data to have an HMAC computed for
 * @param   key             The key to use to generate the HMAC
 * @param   algorithm       The algorithm to use to generate the HMAC (currently ignored because only
 *                          SHA1 is supported)
 * @param   prependSize     True if the data size is to be prepended to the data before hashing
 *
 * @return  HMAC for the specified data using the specified key
 */
std::string Hmac::compute(const std::string& data, const std::string& key, HmacAlgorithm algorithm, bool prependSize) {
    /*
     * Eliminate the unused args warning for algorithm.
     */
    static_cast<void>(algorithm);

    HMAC_CTX hmacContext;
    HMAC_CTX_init(&hmacContext);
    HMAC_Init_ex(&hmacContext, key.c_str(), key.length(), EVP_sha1(), NULL);

    if (data.length() != 0) {
        if (prependSize) {
            uint32_t dataLengthBigEndian = htonl(data.length());
            HMAC_Update(&hmacContext, reinterpret_cast<unsigned char*>(&dataLengthBigEndian), sizeof(uint32_t));
        }
        HMAC_Update(&hmacContext, reinterpret_cast<const unsigned char*>(data.c_str()), data.length());
    }

    unsigned char result[SHA_DIGEST_LENGTH];
    unsigned int resultLength = SHA_DIGEST_LENGTH;
    HMAC_Final(&hmacContext, result, &resultLength);
    HMAC_CTX_cleanup(&hmacContext);

    return std::string(reinterpret_cast<char*>(result), resultLength);
}