HPAVKeyNID.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 HPAVKeyNID (uint8_t NID [], const uint8_t NMK [], signed level);
     *
     *   HPAVKey.h
     *
     *   compute the HomePlugAV compliant Network Identification Key (NID)
     *   for a given Network Membership Key (NMK); return the key in buffer
     *   NID []; the key will be HPAVKEY_NID_LEN bytes as defined in
     *   HPAVKey.h;
     *
     *   unlike the NMK, the NID is 54-bits and includes a 2-bit security
     *   level; See the HomePlug AV Specification for more info;
     *
     *   hash the NMK then rehash the digest 4 times per HomePlug AV
     *   Specification; no salt is used;
     *
     *
     *   Contributor(s);
     *	Charles Maier <cmaier@qca.qualcomm.com>
     *
     *--------------------------------------------------------------------*/

    #ifndef HPAVKEYNID_SOURCE
    #define HPAVKEYNID_SOURCE

    #include <memory.h>

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

    void HPAVKeyNID (uint8_t NID [], const uint8_t NMK [], uint8_t level)

    {
    	struct sha256 sha256;
    	uint8_t digest [SHA256_DIGEST_LENGTH];
    	unsigned rehash = 4;
    	SHA256Reset (&sha256);
    	SHA256Write (&sha256, NMK, HPAVKEY_NMK_LEN);
    	SHA256Fetch (&sha256, digest);
    	while (rehash--)
    	{
    		SHA256Reset (&sha256);
    		SHA256Write (&sha256, digest, sizeof (digest));
    		SHA256Fetch (&sha256, digest);
    	}

    #if 1

    	level <<= 4;
    	digest [HPAVKEY_NID_LEN - 1] >>= 4;
    	digest [HPAVKEY_NID_LEN - 1] |= level;

    #else

    	digest [HPAVKEY_NID_LEN - 1] &= ~0xC0;
    	digest [HPAVKEY_NID_LEN - 1] |= level << 6;

    #endif

    	memcpy (NID, digest, HPAVKEY_NID_LEN);
    	return;
    }

    #endif

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