HPAVKeyDAK.c
Author: cmaier@cmassoc.net

    /*====================================================================*
     *
     *   Copyright (c) 2013 Qualcomm Atheros, Inc.
     *
     *   All rights reserved.
     *
     *   Redistribution and use in source and binary forms, with or
     *   without modification, are permitted (subject to the limitations
     *   in the disclaimer below) provided that the following conditions
     *   are met:
     *
     *   * Redistributions of source code must retain the above copyright
     *     notice, this list of conditions and the following disclaimer.
     *
     *   * 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.
     *
     *   * Neither the name of Qualcomm Atheros nor the names of
     *     its contributors may be used to endorse or promote products
     *     derived from this software without specific prior written
     *     permission.
     *
     *   NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE
     *   GRANTED BY THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE
     *   COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS 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 COPYRIGHT OWNER
     *   OR 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.
     *
     *--------------------------------------------------------------------*/

    /*====================================================================*
     *
     *   void HPAVKeyDAK (uint8_t DAK [], const char * string);
     *
     *   HPAVKey.h
     *
     *   compute the HomePlugAV compliant Device Access Key (DAK) for a
     *   NUL terminated string; return the key in buffer DAK[]; the key
     *   will be HPAVKEY_DAK_LEN bytes as defined in HPAVKey.h;
     *
     *   seed the digest then salt the digest then rehash the digest 999
     *   times per HomePlug AV Specification;
     *
     *
     *   Contributor(s);
     *	Charles Maier <cmaier@qca.qualcomm.com>
     *
     *--------------------------------------------------------------------*/

    #ifndef HPAVKEYDAK_SOURCE
    #define HPAVKEYDAK_SOURCE

    #include <memory.h>

    #include "../key/HPAVKey.h"
    #include "../key/SHA256.h"

    void HPAVKeyDAK (uint8_t DAK [], const char * string)

    {
    	struct sha256 sha256;
    	uint8_t digest [SHA256_DIGEST_LENGTH];
    	const uint8_t secret [] =
    	{
    		0x08,
    		0x85,
    		0x6D,
    		0xAF,
    		0x7C,
    		0xF5,
    		0x81,
    		0x85
    	};
    	unsigned rehash = 999;
    	SHA256Reset (&sha256);
    	SHA256Write (&sha256, string, strlen (string));
    	SHA256Write (&sha256, secret, sizeof (secret));
    	SHA256Fetch (&sha256, digest);
    	while (rehash--)
    	{
    		SHA256Reset (&sha256);
    		SHA256Write (&sha256, digest, sizeof (digest));
    		SHA256Fetch (&sha256, digest);
    	}
    	memcpy (DAK, digest, HPAVKEY_DAK_LEN);
    	return;
    }

    #endif

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