// Copyright 2017 The BoringSSL Authors

//

// 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 <openssl/bn.h>

#include <openssl/bytestring.h>

#include <openssl/mem.h>

#define CHECK(expr)                 \

  do {                              \

    if (!(expr)) {                  \

      printf("%s failed\n", #expr); \

      abort();                      \

    }                               \

  } while (false)

// Basic implementation of mod_exp using square and multiple method.

int mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,

            BN_CTX *ctx) {

  if (BN_is_one(m)) {

    BN_zero(r);

    return 1;

  }

  bssl::UniquePtr<BIGNUM> exp(BN_dup(p));

  bssl::UniquePtr<BIGNUM> base(BN_new());

  if (!exp || !base) {

    return 0;

  }

  if (!BN_one(r) || !BN_nnmod(base.get(), a, m, ctx)) {

    return 0;

  }

  while (!BN_is_zero(exp.get())) {

    if (BN_is_odd(exp.get())) {

      if (!BN_mul(r, r, base.get(), ctx) || !BN_nnmod(r, r, m, ctx)) {

        return 0;

      }

    }

    if (!BN_rshift1(exp.get(), exp.get()) ||

        !BN_mul(base.get(), base.get(), base.get(), ctx) ||

        !BN_nnmod(base.get(), base.get(), m, ctx)) {

      return 0;

    }

  }

  return 1;

}

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *buf, size_t len) {

  CBS cbs, child0, child1, child2;

  uint8_t sign;

  CBS_init(&cbs, buf, len);

  if (!CBS_get_u16_length_prefixed(&cbs, &child0) ||

      !CBS_get_u8(&child0, &sign) ||

      CBS_len(&child0) == 0 ||

      !CBS_get_u16_length_prefixed(&cbs, &child1) ||

      CBS_len(&child1) == 0 ||

      !CBS_get_u16_length_prefixed(&cbs, &child2) ||

      CBS_len(&child2) == 0) {

    return 0;

  }

  // Don't fuzz inputs larger than 512 bytes (4096 bits). This isn't ideal, but

  // the naive `mod_exp` above is somewhat slow, so this otherwise causes the

  // fuzzers to spend a lot of time exploring timeouts.

  if (CBS_len(&child0) > 512 ||

      CBS_len(&child1) > 512 ||

      CBS_len(&child2) > 512) {

    return 0;

  }

  bssl::UniquePtr<BIGNUM> base(

      BN_bin2bn(CBS_data(&child0), CBS_len(&child0), nullptr));

  BN_set_negative(base.get(), sign % 2);

  bssl::UniquePtr<BIGNUM> power(

      BN_bin2bn(CBS_data(&child1), CBS_len(&child1), nullptr));

  bssl::UniquePtr<BIGNUM> modulus(

      BN_bin2bn(CBS_data(&child2), CBS_len(&child2), nullptr));

  if (BN_is_zero(modulus.get())) {

    return 0;

  }

  bssl::UniquePtr<BN_CTX> ctx(BN_CTX_new());

  bssl::UniquePtr<BIGNUM> result(BN_new());

  bssl::UniquePtr<BIGNUM> expected(BN_new());

  CHECK(ctx);

  CHECK(result);

  CHECK(expected);

  CHECK(mod_exp(expected.get(), base.get(), power.get(), modulus.get(),

                ctx.get()));

  CHECK(BN_mod_exp(result.get(), base.get(), power.get(), modulus.get(),

                   ctx.get()));

  CHECK(BN_cmp(result.get(), expected.get()) == 0);

  if (BN_is_odd(modulus.get())) {

    bssl::UniquePtr<BN_MONT_CTX> mont(

        BN_MONT_CTX_new_for_modulus(modulus.get(), ctx.get()));

    CHECK(mont);

    // `BN_mod_exp_mont` and `BN_mod_exp_mont_consttime` require reduced inputs.

    CHECK(BN_nnmod(base.get(), base.get(), modulus.get(), ctx.get()));

    CHECK(BN_mod_exp_mont(result.get(), base.get(), power.get(), modulus.get(),

                          ctx.get(), mont.get()));

    CHECK(BN_cmp(result.get(), expected.get()) == 0);

    CHECK(BN_mod_exp_mont_consttime(result.get(), base.get(), power.get(),

                                    modulus.get(), ctx.get(), mont.get()));

    CHECK(BN_cmp(result.get(), expected.get()) == 0);

  }

  uint8_t *data = (uint8_t *)OPENSSL_malloc(BN_num_bytes(result.get()));

  BN_bn2bin(result.get(), data);

  OPENSSL_free(data);

  return 0;

}