// Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//     https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

#include <assert.h>

#include <string.h>

#include "internal.h"

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

static_assert(16 % sizeof(crypto_word_t) == 0,

              "block cannot be divided into crypto_word_t");

// increment upper 96 bits of 128-bit counter by 1

static void ctr96_inc(uint8_t *counter) {

  uint32_t n = 12, c = 1;

  do {

    --n;

    c += counter[n];

    counter[n] = (uint8_t) c;

    c >>= 8;

  } while (n);

}

void CRYPTO_ctr128_encrypt_ctr32(const uint8_t *in, uint8_t *out, size_t len,

                                 const AES_KEY *key, uint8_t ivec[16],

                                 uint8_t ecount_buf[16], unsigned int *num,

                                 ctr128_f func) {

  unsigned int n, ctr32;

  assert(key && ecount_buf && num);

  assert(len == 0 || (in && out));

  assert(*num < 16);

  n = *num;

  while (n && len) {

    *(out++) = *(in++) ^ ecount_buf[n];

    --len;

    n = (n + 1) % 16;

  }

  ctr32 = CRYPTO_load_u32_be(ivec + 12);

  while (len >= 16) {

    size_t blocks = len / 16;

    // 1<<28 is just a not-so-small yet not-so-large number...

    // Below condition is practically never met, but it has to

    // be checked for code correctness.

    if (sizeof(size_t) > sizeof(unsigned int) && blocks > (1U << 28)) {

      blocks = (1U << 28);

    }

    // As (*func) operates on 32-bit counter, caller

    // has to handle overflow. 'if' below detects the

    // overflow, which is then handled by limiting the

    // amount of blocks to the exact overflow point...

    ctr32 += (uint32_t)blocks;

    if (ctr32 < blocks) {

      blocks -= ctr32;

      ctr32 = 0;

    }

    (*func)(in, out, blocks, key, ivec);

    // (*func) does not update ivec, caller does:

    CRYPTO_store_u32_be(ivec + 12, ctr32);

    // ... overflow was detected, propagate carry.

    if (ctr32 == 0) {

      ctr96_inc(ivec);

    }

    blocks *= 16;

    len -= blocks;

    out += blocks;

    in += blocks;

  }

  if (len) {

    OPENSSL_memset(ecount_buf, 0, 16);

    (*func)(ecount_buf, ecount_buf, 1, key, ivec);

    ++ctr32;

    CRYPTO_store_u32_be(ivec + 12, ctr32);

    if (ctr32 == 0) {

      ctr96_inc(ivec);

    }

    while (len--) {

      out[n] = in[n] ^ ecount_buf[n];

      ++n;

    }

  }

  *num = n;

}