/* gcm.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 Niels Möller

   Copyright (C) 2018 Red Hat, Inc.

   Contributed by Nikos Mavrogiannopoulos

   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 <assert.h>

#include <stdlib.h>

#include <string.h>

#include "gcm.h"

#include "ghash-internal.h"

#include "memxor.h"

#include "nettle-internal.h"

#include "macros.h"

#include "ctr-internal.h"

#include "block-internal.h"

#include "bswap-internal.h"

/* Initialization of GCM.

 * @ctx: The context of GCM

 * @cipher: The context of the underlying block cipher

 * @f: The underlying cipher encryption function

 */

void

gcm_set_key(struct gcm_key *key,

      const void *cipher, nettle_cipher_func *f)

{

  static const union nettle_block16 zero_block;

  union nettle_block16 key_block;

  f (cipher, GCM_BLOCK_SIZE, key_block.b, zero_block.b);

  _ghash_set_key (key, &key_block);

}

/* Call _ghash_update, with zero padding of any partial final block. */

static void

gcm_hash (const struct gcm_key *key, union nettle_block16 *x,

    size_t length, const uint8_t *data) {

  data = _ghash_update (key, x, length / GCM_BLOCK_SIZE, data);

  length &= (GCM_BLOCK_SIZE - 1);

  if (length > 0)

    {

      union nettle_block16 block;

      block16_zero (&block);

      memcpy (block.b, data, length);

      _ghash_update (key, x, 1, block.b);

    }

}

static void

gcm_hash_sizes(const struct gcm_key *key, union nettle_block16 *x,

         uint64_t auth_size, uint64_t data_size)

{

  union nettle_block16 buffer;

  data_size *= 8;

  auth_size *= 8;

  buffer.u64[0] = bswap64_if_le (auth_size);

  buffer.u64[1] = bswap64_if_le (data_size);

  _ghash_update (key, x, 1, buffer.b);

}

/* NOTE: The key is needed only if length != GCM_IV_SIZE */

void

gcm_set_iv(struct gcm_ctx *ctx, const struct gcm_key *key,

     size_t length, const uint8_t *iv)

{

  if (length == GCM_IV_SIZE)

    {

      memcpy (ctx->iv.b, iv, GCM_BLOCK_SIZE - 4);

      ctx->iv.b[GCM_BLOCK_SIZE - 4] = 0;

      ctx->iv.b[GCM_BLOCK_SIZE - 3] = 0;

      ctx->iv.b[GCM_BLOCK_SIZE - 2] = 0;

      ctx->iv.b[GCM_BLOCK_SIZE - 1] = 1;

    }

  else

    {

      block16_zero(&ctx->iv);

      gcm_hash(key, &ctx->iv, length, iv);

      gcm_hash_sizes(key, &ctx->iv, 0, length);

    }

  ctx->ctr = ctx->iv;

  /* Increment the rightmost 32 bits. */

  INCREMENT (4, ctx->ctr.b + GCM_BLOCK_SIZE - 4);

  /* Reset the rest of the message-dependent state. */

  block16_zero(&ctx->x);

  ctx->auth_size = ctx->data_size = 0;

}

void

gcm_update(struct gcm_ctx *ctx, const struct gcm_key *key,

     size_t length, const uint8_t *data)

{

  assert(ctx->auth_size % GCM_BLOCK_SIZE == 0);

  assert(ctx->data_size == 0);

  gcm_hash(key, &ctx->x, length, data);

  ctx->auth_size += length;

}

static nettle_fill16_func gcm_fill;

#if WORDS_BIGENDIAN

static void

gcm_fill(uint8_t *ctr, size_t blocks, union nettle_block16 *buffer)

{

  uint64_t hi, mid;

  uint32_t lo;

  size_t i;

  hi = READ_UINT64(ctr);

  mid = (uint64_t) READ_UINT32(ctr + 8) << 32;

  lo = READ_UINT32(ctr + 12);

  for (i = 0; i < blocks; i++)

    {

      buffer[i].u64[0] = hi;

      buffer[i].u64[1] = mid + lo++;

    }

  WRITE_UINT32(ctr + 12, lo);

}

#elif HAVE_BUILTIN_BSWAP64

/* Assume __builtin_bswap32 is also available */

static void

gcm_fill(uint8_t *ctr, size_t blocks, union nettle_block16 *buffer)

{

  uint64_t hi, mid;

  uint32_t lo;

  size_t i;

  hi = LE_READ_UINT64(ctr);

  mid = LE_READ_UINT32(ctr + 8);

  lo = READ_UINT32(ctr + 12);

  for (i = 0; i < blocks; i++)

    {

      buffer[i].u64[0] = hi;

      buffer[i].u64[1] = mid + ((uint64_t)__builtin_bswap32(lo) << 32);

      lo++;

    }

  WRITE_UINT32(ctr + 12, lo);

}

#else

static void

gcm_fill(uint8_t *ctr, size_t blocks, union nettle_block16 *buffer)

{

  uint32_t c;

  c = READ_UINT32(ctr + GCM_BLOCK_SIZE - 4);

  for (; blocks-- > 0; buffer++, c++)

    {

      memcpy(buffer->b, ctr, GCM_BLOCK_SIZE - 4);

      WRITE_UINT32(buffer->b + GCM_BLOCK_SIZE - 4, c);

    }

  WRITE_UINT32(ctr + GCM_BLOCK_SIZE - 4, c);

}

#endif

void

gcm_encrypt (struct gcm_ctx *ctx, const struct gcm_key *key,

       const void *cipher, nettle_cipher_func *f,

       size_t length, uint8_t *dst, const uint8_t *src)

{

  assert(ctx->data_size % GCM_BLOCK_SIZE == 0);

  _nettle_ctr_crypt16(cipher, f, gcm_fill, ctx->ctr.b, length, dst, src);

  gcm_hash(key, &ctx->x, length, dst);

  ctx->data_size += length;

}

void

gcm_decrypt(struct gcm_ctx *ctx, const struct gcm_key *key,

      const void *cipher, nettle_cipher_func *f,

      size_t length, uint8_t *dst, const uint8_t *src)

{

  assert(ctx->data_size % GCM_BLOCK_SIZE == 0);

  gcm_hash(key, &ctx->x, length, src);

  _nettle_ctr_crypt16(cipher, f, gcm_fill, ctx->ctr.b, length, dst, src);

  ctx->data_size += length;

}

void

gcm_digest(struct gcm_ctx *ctx, const struct gcm_key *key,

     const void *cipher, nettle_cipher_func *f,

     size_t length, uint8_t *digest)

{

  union nettle_block16 buffer;

  assert (length <= GCM_BLOCK_SIZE);

  gcm_hash_sizes(key, &ctx->x, ctx->auth_size, ctx->data_size);

  f (cipher, GCM_BLOCK_SIZE, buffer.b, ctx->iv.b);

  block16_xor (&buffer, &ctx->x);

  memcpy (digest, buffer.b, length);

  return;

}