/* ghash-set-key.c

   Galois counter mode, specified by NIST,

   http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf

   See also the gcm paper at

   http://www.cryptobarn.com/papers/gcm-spec.pdf.

   Copyright (C) 2011 Katholieke Universiteit Leuven

   Copyright (C) 2011, 2013, 2018, 2022 Niels Möller

   Copyright (C) 2018 Red Hat, Inc.

   This file is part of GNU Nettle.

   GNU Nettle is free software: you can redistribute it and/or

   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free

       Software Foundation; either version 3 of the License, or (at your

       option) any later version.

   or

     * 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.

   or both in parallel, as here.

   GNU Nettle 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 copies of the GNU General Public License and

   the GNU Lesser General Public License along with this program.  If

   not, see http://www.gnu.org/licenses/.

*/

#if HAVE_CONFIG_H

# include "config.h"

#endif

#include "ghash-internal.h"

#include "block-internal.h"

/* For fat builds */

#if HAVE_NATIVE_ghash_set_key

void

_nettle_ghash_set_key_c (struct gcm_key *ctx, const union nettle_block16 *key);

#define _nettle_ghash_set_key _nettle_ghash_set_key_c

#endif

/* Implements a lookup table for processors without carryless-mul

   instruction. */

void

_ghash_set_key (struct gcm_key *ctx, const union nettle_block16 *key)

{

  /* Middle element if GCM_TABLE_BITS > 0, otherwise the first

     element */

  unsigned i = (1<<GCM_TABLE_BITS)/2;

  block16_zero (&ctx->h[0]);

  ctx->h[i] = *key;

  /* Algorithm 3 from the gcm paper. First do powers of two, then do

     the rest by adding. */

  while (i /= 2)

    block16_mulx_ghash (&ctx->h[i], &ctx->h[2*i]);

  for (i = 2; i < 1<<GCM_TABLE_BITS; i *= 2)

    {

      unsigned j;

      for (j = 1; j < i; j++)

  block16_xor3 (&ctx->h[i+j], &ctx->h[i], &ctx->h[j]);

    }

}