/* Copyright (c) 2016, Google Inc.

 *

 * Permission to use, copy, modify, and/or distribute this software for any

 * purpose with or without fee is hereby granted, provided that the above

 * copyright notice and this permission notice appear in all copies.

 *

 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY

 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION

 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN

 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/base.h>

#include <assert.h>

#include <string.h>

#include "internal.h"

#include "../../internal.h"

// byte_reverse reverses the order of the bytes in |b->c|.

static void byte_reverse(uint8_t b[16]) {

  uint64_t hi = CRYPTO_load_u64_le(b);

  uint64_t lo = CRYPTO_load_u64_le(b + 8);

  CRYPTO_store_u64_le(b, CRYPTO_bswap8(lo));

  CRYPTO_store_u64_le(b + 8, CRYPTO_bswap8(hi));

}

// reverse_and_mulX_ghash interprets |b| as a reversed element of the GHASH

// field, multiplies that by 'x' and serialises the result back into |b|, but

// with GHASH's backwards bit ordering.

static void reverse_and_mulX_ghash(uint8_t b[16]) {

  uint64_t hi = CRYPTO_load_u64_le(b);

  uint64_t lo = CRYPTO_load_u64_le(b + 8);

  const crypto_word_t carry = constant_time_eq_w(hi & 1, 1);

  hi >>= 1;

  hi |= lo << 63;

  lo >>= 1;

  lo ^= ((uint64_t) constant_time_select_w(carry, 0xe1, 0)) << 56;

  CRYPTO_store_u64_le(b, CRYPTO_bswap8(lo));

  CRYPTO_store_u64_le(b + 8, CRYPTO_bswap8(hi));

}

// POLYVAL(H, X_1, ..., X_n) =

// ByteReverse(GHASH(mulX_GHASH(ByteReverse(H)), ByteReverse(X_1), ...,

// ByteReverse(X_n))).

//

// See https://www.rfc-editor.org/rfc/rfc8452.html#appendix-A.

void CRYPTO_POLYVAL_init(struct polyval_ctx *ctx, const uint8_t key[16]) {

  alignas(8) uint8_t H[16];

  OPENSSL_memcpy(H, key, 16);

  reverse_and_mulX_ghash(H);

  int is_avx;

  CRYPTO_ghash_init(&ctx->gmult, &ctx->ghash, ctx->Htable, &is_avx, H);

  OPENSSL_memset(&ctx->S, 0, sizeof(ctx->S));

}

void CRYPTO_POLYVAL_update_blocks(struct polyval_ctx *ctx, const uint8_t *in,

                                  size_t in_len) {

  assert((in_len & 15) == 0);

  alignas(8) uint8_t buf[32 * 16];

  while (in_len > 0) {

    size_t todo = in_len;

    if (todo > sizeof(buf)) {

      todo = sizeof(buf);

    }

    OPENSSL_memcpy(buf, in, todo);

    in += todo;

    in_len -= todo;

    size_t blocks = todo / 16;

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

      byte_reverse(buf + 16 * i);

    }

    ctx->ghash(ctx->S, ctx->Htable, buf, todo);

  }

}

void CRYPTO_POLYVAL_finish(const struct polyval_ctx *ctx, uint8_t out[16]) {

  OPENSSL_memcpy(out, &ctx->S, 16);

  byte_reverse(out);

}