/* Copyright (c) 2017, 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/ctrdrbg.h>

#include <assert.h>

#include <openssl/mem.h>

#include "internal.h"

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

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

// Section references in this file refer to SP 800-90Ar1:

// http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-90Ar1.pdf

// See table 3.

static const uint64_t kMaxReseedCount = UINT64_C(1) << 48;

CTR_DRBG_STATE *CTR_DRBG_new(const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],

                             const uint8_t *personalization,

                             size_t personalization_len) {

  CTR_DRBG_STATE *drbg = OPENSSL_malloc(sizeof(CTR_DRBG_STATE));

  if (drbg == NULL ||

      !CTR_DRBG_init(drbg, entropy, personalization, personalization_len)) {

    CTR_DRBG_free(drbg);

    return NULL;

  }

  return drbg;

}

void CTR_DRBG_free(CTR_DRBG_STATE *state) { OPENSSL_free(state); }

int CTR_DRBG_init(CTR_DRBG_STATE *drbg,

                  const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],

                  const uint8_t *personalization, size_t personalization_len) {

  // Section 10.2.1.3.1

  if (personalization_len > CTR_DRBG_ENTROPY_LEN) {

    return 0;

  }

  uint8_t seed_material[CTR_DRBG_ENTROPY_LEN];

  OPENSSL_memcpy(seed_material, entropy, CTR_DRBG_ENTROPY_LEN);

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

    seed_material[i] ^= personalization[i];

  }

  // Section 10.2.1.2

  // kInitMask is the result of encrypting blocks with big-endian value 1, 2

  // and 3 with the all-zero AES-256 key.

  static const uint8_t kInitMask[CTR_DRBG_ENTROPY_LEN] = {

      0x53, 0x0f, 0x8a, 0xfb, 0xc7, 0x45, 0x36, 0xb9, 0xa9, 0x63, 0xb4, 0xf1,

      0xc4, 0xcb, 0x73, 0x8b, 0xce, 0xa7, 0x40, 0x3d, 0x4d, 0x60, 0x6b, 0x6e,

      0x07, 0x4e, 0xc5, 0xd3, 0xba, 0xf3, 0x9d, 0x18, 0x72, 0x60, 0x03, 0xca,

      0x37, 0xa6, 0x2a, 0x74, 0xd1, 0xa2, 0xf5, 0x8e, 0x75, 0x06, 0x35, 0x8e,

  };

  for (size_t i = 0; i < sizeof(kInitMask); i++) {

    seed_material[i] ^= kInitMask[i];

  }

  drbg->ctr = aes_ctr_set_key(&drbg->ks, NULL, &drbg->block, seed_material, 32);

  OPENSSL_memcpy(drbg->counter, seed_material + 32, 16);

  drbg->reseed_counter = 1;

  return 1;

}

static_assert(CTR_DRBG_ENTROPY_LEN % AES_BLOCK_SIZE == 0,

              "not a multiple of AES block size");

// ctr_inc adds |n| to the last four bytes of |drbg->counter|, treated as a

// big-endian number.

static void ctr32_add(CTR_DRBG_STATE *drbg, uint32_t n) {

  uint32_t ctr = CRYPTO_load_u32_be(drbg->counter + 12);

  CRYPTO_store_u32_be(drbg->counter + 12, ctr + n);

}

static int ctr_drbg_update(CTR_DRBG_STATE *drbg, const uint8_t *data,

                           size_t data_len) {

  // Per section 10.2.1.2, |data_len| must be |CTR_DRBG_ENTROPY_LEN|. Here, we

  // allow shorter inputs and right-pad them with zeros. This is equivalent to

  // the specified algorithm but saves a copy in |CTR_DRBG_generate|.

  if (data_len > CTR_DRBG_ENTROPY_LEN) {

    return 0;

  }

  uint8_t temp[CTR_DRBG_ENTROPY_LEN];

  for (size_t i = 0; i < CTR_DRBG_ENTROPY_LEN; i += AES_BLOCK_SIZE) {

    ctr32_add(drbg, 1);

    drbg->block(drbg->counter, temp + i, &drbg->ks);

  }

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

    temp[i] ^= data[i];

  }

  drbg->ctr = aes_ctr_set_key(&drbg->ks, NULL, &drbg->block, temp, 32);

  OPENSSL_memcpy(drbg->counter, temp + 32, 16);

  return 1;

}

int CTR_DRBG_reseed(CTR_DRBG_STATE *drbg,

                    const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],

                    const uint8_t *additional_data,

                    size_t additional_data_len) {

  // Section 10.2.1.4

  uint8_t entropy_copy[CTR_DRBG_ENTROPY_LEN];

  if (additional_data_len > 0) {

    if (additional_data_len > CTR_DRBG_ENTROPY_LEN) {

      return 0;

    }

    OPENSSL_memcpy(entropy_copy, entropy, CTR_DRBG_ENTROPY_LEN);

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

      entropy_copy[i] ^= additional_data[i];

    }

    entropy = entropy_copy;

  }

  if (!ctr_drbg_update(drbg, entropy, CTR_DRBG_ENTROPY_LEN)) {

    return 0;

  }

  drbg->reseed_counter = 1;

  return 1;

}

int CTR_DRBG_generate(CTR_DRBG_STATE *drbg, uint8_t *out, size_t out_len,

                      const uint8_t *additional_data,

                      size_t additional_data_len) {

  // See 9.3.1

  if (out_len > CTR_DRBG_MAX_GENERATE_LENGTH) {

    return 0;

  }

  // See 10.2.1.5.1

  if (drbg->reseed_counter > kMaxReseedCount) {

    return 0;

  }

  if (additional_data_len != 0 &&

      !ctr_drbg_update(drbg, additional_data, additional_data_len)) {

    return 0;

  }

  // kChunkSize is used to interact better with the cache. Since the AES-CTR

  // code assumes that it's encrypting rather than just writing keystream, the

  // buffer has to be zeroed first. Without chunking, large reads would zero

  // the whole buffer, flushing the L1 cache, and then do another pass (missing

  // the cache every time) to “encrypt” it. The code can avoid this by

  // chunking.

  static const size_t kChunkSize = 8 * 1024;

  while (out_len >= AES_BLOCK_SIZE) {

    size_t todo = kChunkSize;

    if (todo > out_len) {

      todo = out_len;

    }

    todo &= ~(AES_BLOCK_SIZE-1);

    const size_t num_blocks = todo / AES_BLOCK_SIZE;

    if (drbg->ctr) {

      OPENSSL_memset(out, 0, todo);

      ctr32_add(drbg, 1);

      drbg->ctr(out, out, num_blocks, &drbg->ks, drbg->counter);

      ctr32_add(drbg, (uint32_t)(num_blocks - 1));

    } else {

      for (size_t i = 0; i < todo; i += AES_BLOCK_SIZE) {

        ctr32_add(drbg, 1);

        drbg->block(drbg->counter, out + i, &drbg->ks);

      }

    }

    out += todo;

    out_len -= todo;

  }

  if (out_len > 0) {

    uint8_t block[AES_BLOCK_SIZE];

    ctr32_add(drbg, 1);

    drbg->block(drbg->counter, block, &drbg->ks);

    OPENSSL_memcpy(out, block, out_len);

  }

  // Right-padding |additional_data| in step 2.2 is handled implicitly by

  // |ctr_drbg_update|, to save a copy.

  if (!ctr_drbg_update(drbg, additional_data, additional_data_len)) {

    return 0;

  }

  drbg->reseed_counter++;

  FIPS_service_indicator_update_state();

  return 1;

}

void CTR_DRBG_clear(CTR_DRBG_STATE *drbg) {

  OPENSSL_cleanse(drbg, sizeof(CTR_DRBG_STATE));

}