// Copyright 1995-2016 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 <openssl/dh.h>

#include <string.h>

#include <iterator>

#include <openssl/bn.h>

#include <openssl/digest.h>

#include <openssl/err.h>

#include <openssl/mem.h>

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

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

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

#include "internal.h"

DH *DH_new(void) {

  DH *dh = reinterpret_cast<DH *>(OPENSSL_zalloc(sizeof(DH)));

  if (dh == nullptr) {

    return nullptr;

  }

  CRYPTO_MUTEX_init(&dh->method_mont_p_lock);

  dh->references = 1;

  return dh;

}

void DH_free(DH *dh) {

  if (dh == nullptr) {

    return;

  }

  if (!CRYPTO_refcount_dec_and_test_zero(&dh->references)) {

    return;

  }

  BN_MONT_CTX_free(dh->method_mont_p);

  BN_clear_free(dh->p);

  BN_clear_free(dh->g);

  BN_clear_free(dh->q);

  BN_clear_free(dh->pub_key);

  BN_clear_free(dh->priv_key);

  CRYPTO_MUTEX_cleanup(&dh->method_mont_p_lock);

  OPENSSL_free(dh);

}

unsigned DH_bits(const DH *dh) { return BN_num_bits(dh->p); }

const BIGNUM *DH_get0_pub_key(const DH *dh) { return dh->pub_key; }

const BIGNUM *DH_get0_priv_key(const DH *dh) { return dh->priv_key; }

const BIGNUM *DH_get0_p(const DH *dh) { return dh->p; }

const BIGNUM *DH_get0_q(const DH *dh) { return dh->q; }

const BIGNUM *DH_get0_g(const DH *dh) { return dh->g; }

void DH_get0_key(const DH *dh, const BIGNUM **out_pub_key,

                 const BIGNUM **out_priv_key) {

  if (out_pub_key != nullptr) {

    *out_pub_key = dh->pub_key;

  }

  if (out_priv_key != nullptr) {

    *out_priv_key = dh->priv_key;

  }

}

int DH_set0_key(DH *dh, BIGNUM *pub_key, BIGNUM *priv_key) {

  if (pub_key != nullptr) {

    BN_free(dh->pub_key);

    dh->pub_key = pub_key;

  }

  if (priv_key != nullptr) {

    BN_free(dh->priv_key);

    dh->priv_key = priv_key;

  }

  return 1;

}

void DH_get0_pqg(const DH *dh, const BIGNUM **out_p, const BIGNUM **out_q,

                 const BIGNUM **out_g) {

  if (out_p != nullptr) {

    *out_p = dh->p;

  }

  if (out_q != nullptr) {

    *out_q = dh->q;

  }

  if (out_g != nullptr) {

    *out_g = dh->g;

  }

}

int DH_set0_pqg(DH *dh, BIGNUM *p, BIGNUM *q, BIGNUM *g) {

  if ((dh->p == nullptr && p == nullptr) ||

      (dh->g == nullptr && g == nullptr)) {

    return 0;

  }

  if (p != nullptr) {

    BN_free(dh->p);

    dh->p = p;

  }

  if (q != nullptr) {

    BN_free(dh->q);

    dh->q = q;

  }

  if (g != nullptr) {

    BN_free(dh->g);

    dh->g = g;

  }

  // Invalidate the cached Montgomery parameters.

  BN_MONT_CTX_free(dh->method_mont_p);

  dh->method_mont_p = nullptr;

  return 1;

}

int DH_set_length(DH *dh, unsigned priv_length) {

  dh->priv_length = priv_length;

  return 1;

}

int DH_generate_key(DH *dh) {

  boringssl_ensure_ffdh_self_test();

  if (!dh_check_params_fast(dh)) {

    return 0;

  }

  int ok = 0;

  bool generate_new_key = false;

  BIGNUM *pub_key = nullptr, *priv_key = nullptr;

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

  if (ctx == nullptr) {

    goto err;

  }

  if (dh->priv_key == nullptr) {

    priv_key = BN_new();

    if (priv_key == nullptr) {

      goto err;

    }

    generate_new_key = true;

  } else {

    priv_key = dh->priv_key;

  }

  if (dh->pub_key == nullptr) {

    pub_key = BN_new();

    if (pub_key == nullptr) {

      goto err;

    }

  } else {

    pub_key = dh->pub_key;

  }

  if (!BN_MONT_CTX_set_locked(&dh->method_mont_p, &dh->method_mont_p_lock,

                              dh->p, ctx.get())) {

    goto err;

  }

  if (generate_new_key) {

    if (dh->q) {

      // Section 5.6.1.1.4 of SP 800-56A Rev3 generates a private key uniformly

      // from [1, min(2^N-1, q-1)].

      //

      // Although SP 800-56A Rev3 now permits a private key length N,

      // |dh->priv_length| historically was ignored when q is available. We

      // continue to ignore it and interpret such a configuration as N = len(q).

      if (!BN_rand_range_ex(priv_key, 1, dh->q)) {

        goto err;

      }

    } else {

      // If q is unspecified, we expect p to be a safe prime, with g generating

      // the (p-1)/2 subgroup. So, we use q = (p-1)/2. (If g generates a smaller

      // prime-order subgroup, q will still divide (p-1)/2.)

      //

      // We set N from |dh->priv_length|. Section 5.6.1.1.4 of SP 800-56A Rev3

      // says to reject N > len(q), or N > num_bits(p) - 1. However, this logic

      // originally aligned with PKCS#3, which allows num_bits(p). Instead, we

      // clamp |dh->priv_length| before invoking the algorithm.

      // Compute M = min(2^N, q).

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

      if (priv_key_limit == nullptr) {

        goto err;

      }

      if (dh->priv_length == 0 || dh->priv_length >= BN_num_bits(dh->p) - 1) {

        // M = q = (p - 1) / 2.

        if (!BN_rshift1(priv_key_limit.get(), dh->p)) {

          goto err;

        }

      } else {

        // M = 2^N.

        if (!BN_set_bit(priv_key_limit.get(), dh->priv_length)) {

          goto err;

        }

      }

      // Choose a private key uniformly from [1, M-1].

      if (!BN_rand_range_ex(priv_key, 1, priv_key_limit.get())) {

        goto err;

      }

    }

  }

  if (!BN_mod_exp_mont_consttime(pub_key, dh->g, priv_key, dh->p, ctx.get(),

                                 dh->method_mont_p)) {

    goto err;

  }

  dh->pub_key = pub_key;

  dh->priv_key = priv_key;

  ok = 1;

err:

  if (ok != 1) {

    OPENSSL_PUT_ERROR(DH, ERR_R_BN_LIB);

  }

  if (dh->pub_key == nullptr) {

    BN_free(pub_key);

  }

  if (dh->priv_key == nullptr) {

    BN_free(priv_key);

  }

  return ok;

}

static int dh_compute_key(DH *dh, BIGNUM *out_shared_key,

                          const BIGNUM *peers_key, BN_CTX *ctx) {

  if (!dh_check_params_fast(dh)) {

    return 0;

  }

  if (dh->priv_key == nullptr) {

    OPENSSL_PUT_ERROR(DH, DH_R_NO_PRIVATE_VALUE);

    return 0;

  }

  int check_result;

  if (!DH_check_pub_key(dh, peers_key, &check_result) || check_result) {

    OPENSSL_PUT_ERROR(DH, DH_R_INVALID_PUBKEY);

    return 0;

  }

  bssl::BN_CTXScope scope(ctx);

  BIGNUM *p_minus_1 = BN_CTX_get(ctx);

  if (!p_minus_1 ||

      !BN_MONT_CTX_set_locked(&dh->method_mont_p, &dh->method_mont_p_lock,

                              dh->p, ctx)) {

    return 0;

  }

  if (!BN_mod_exp_mont_consttime(out_shared_key, peers_key, dh->priv_key, dh->p,

                                 ctx, dh->method_mont_p) ||

      !BN_copy(p_minus_1, dh->p) || !BN_sub_word(p_minus_1, 1)) {

    OPENSSL_PUT_ERROR(DH, ERR_R_BN_LIB);

    return 0;

  }

  // This performs the check required by SP 800-56Ar3 section 5.7.1.1 step two.

  if (BN_cmp_word(out_shared_key, 1) <= 0 ||

      BN_cmp(out_shared_key, p_minus_1) == 0) {

    OPENSSL_PUT_ERROR(DH, DH_R_INVALID_PUBKEY);

    return 0;

  }

  return 1;

}

int dh_compute_key_padded_no_self_test(unsigned char *out,

                                       const BIGNUM *peers_key, DH *dh) {

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

  if (ctx == nullptr) {

    return -1;

  }

  bssl::BN_CTXScope scope(ctx.get());

  int dh_size = DH_size(dh);

  BIGNUM *shared_key = BN_CTX_get(ctx.get());

  if (shared_key == nullptr ||

      !dh_compute_key(dh, shared_key, peers_key, ctx.get()) ||

      !BN_bn2bin_padded(out, dh_size, shared_key)) {

    return -1;

  }

  return dh_size;

}

int DH_compute_key_padded(unsigned char *out, const BIGNUM *peers_key, DH *dh) {

  boringssl_ensure_ffdh_self_test();

  return dh_compute_key_padded_no_self_test(out, peers_key, dh);

}

int DH_compute_key(unsigned char *out, const BIGNUM *peers_key, DH *dh) {

  boringssl_ensure_ffdh_self_test();

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

  if (ctx == nullptr) {

    return -1;

  }

  bssl::BN_CTXScope scope(ctx.get());

  BIGNUM *shared_key = BN_CTX_get(ctx.get());

  if (shared_key == nullptr ||

      !dh_compute_key(dh, shared_key, peers_key, ctx.get())) {

    return -1;

  }

  // A |BIGNUM|'s byte count fits in |int|.

  return static_cast<int>(BN_bn2bin(shared_key, out));

}

int DH_compute_key_hashed(DH *dh, uint8_t *out, size_t *out_len,

                          size_t max_out_len, const BIGNUM *peers_key,

                          const EVP_MD *digest) {

  *out_len = SIZE_MAX;

  const size_t digest_len = EVP_MD_size(digest);

  if (digest_len > max_out_len) {

    return 0;

  }

  FIPS_service_indicator_lock_state();

  int ret = 0;

  const size_t dh_len = DH_size(dh);

  uint8_t *shared_bytes = reinterpret_cast<uint8_t *>(OPENSSL_malloc(dh_len));

  unsigned out_len_unsigned;

  if (!shared_bytes ||

      // SP 800-56A is ambiguous about whether the output should be padded prior

      // to revision three. But revision three, section C.1, awkwardly specifies

      // padding to the length of p.

      //

      // Also, padded output avoids side-channels, so is always strongly

      // advisable.

      DH_compute_key_padded(shared_bytes, peers_key, dh) != (int)dh_len ||

      !EVP_Digest(shared_bytes, dh_len, out, &out_len_unsigned, digest,

                  nullptr) ||

      out_len_unsigned != digest_len) {

    goto err;

  }

  *out_len = digest_len;

  ret = 1;

err:

  FIPS_service_indicator_unlock_state();

  OPENSSL_free(shared_bytes);

  return ret;

}

int DH_size(const DH *dh) { return BN_num_bytes(dh->p); }

unsigned DH_num_bits(const DH *dh) { return BN_num_bits(dh->p); }

int DH_up_ref(DH *dh) {

  CRYPTO_refcount_inc(&dh->references);

  return 1;

}

DH *DH_get_rfc7919_2048(void) {

  // This is the prime from https://tools.ietf.org/html/rfc7919#appendix-A.1,

  // which is specifically approved for FIPS in appendix D of SP 800-56Ar3.

  static const BN_ULONG kFFDHE2048Data[] = {

      TOBN(0xffffffff, 0xffffffff), TOBN(0x886b4238, 0x61285c97),

      TOBN(0xc6f34a26, 0xc1b2effa), TOBN(0xc58ef183, 0x7d1683b2),

      TOBN(0x3bb5fcbc, 0x2ec22005), TOBN(0xc3fe3b1b, 0x4c6fad73),

      TOBN(0x8e4f1232, 0xeef28183), TOBN(0x9172fe9c, 0xe98583ff),

      TOBN(0xc03404cd, 0x28342f61), TOBN(0x9e02fce1, 0xcdf7e2ec),

      TOBN(0x0b07a7c8, 0xee0a6d70), TOBN(0xae56ede7, 0x6372bb19),

      TOBN(0x1d4f42a3, 0xde394df4), TOBN(0xb96adab7, 0x60d7f468),

      TOBN(0xd108a94b, 0xb2c8e3fb), TOBN(0xbc0ab182, 0xb324fb61),

      TOBN(0x30acca4f, 0x483a797a), TOBN(0x1df158a1, 0x36ade735),

      TOBN(0xe2a689da, 0xf3efe872), TOBN(0x984f0c70, 0xe0e68b77),

      TOBN(0xb557135e, 0x7f57c935), TOBN(0x85636555, 0x3ded1af3),

      TOBN(0x2433f51f, 0x5f066ed0), TOBN(0xd3df1ed5, 0xd5fd6561),

      TOBN(0xf681b202, 0xaec4617a), TOBN(0x7d2fe363, 0x630c75d8),

      TOBN(0xcc939dce, 0x249b3ef9), TOBN(0xa9e13641, 0x146433fb),

      TOBN(0xd8b9c583, 0xce2d3695), TOBN(0xafdc5620, 0x273d3cf1),

      TOBN(0xadf85458, 0xa2bb4a9a), TOBN(0xffffffff, 0xffffffff),

  };

  bssl::UniquePtr<BIGNUM> ffdhe2048_p(BN_new());

  bssl::UniquePtr<BIGNUM> ffdhe2048_q(BN_new());

  bssl::UniquePtr<BIGNUM> ffdhe2048_g(BN_new());

  bssl::UniquePtr<DH> dh(DH_new());

  if (!ffdhe2048_p || !ffdhe2048_q || !ffdhe2048_g || !dh) {

    return nullptr;

  }

  bn_set_static_words(ffdhe2048_p.get(), kFFDHE2048Data,

                      std::size(kFFDHE2048Data));

  if (!BN_rshift1(ffdhe2048_q.get(), ffdhe2048_p.get()) ||

      !BN_set_word(ffdhe2048_g.get(), 2) ||

      !DH_set0_pqg(dh.get(), ffdhe2048_p.get(), ffdhe2048_q.get(),

                   ffdhe2048_g.get())) {

    return nullptr;

  }

  // |DH_set0_pqg| takes ownership on success.

  ffdhe2048_p.release();

  ffdhe2048_q.release();

  ffdhe2048_g.release();

  return dh.release();

}