// Copyright 2002-2016 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/ecdsa.h>

#include <assert.h>

#include <string.h>

#include <openssl/bn.h>

#include <openssl/err.h>

#include <openssl/mem.h>

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

#include "../bcm_interface.h"

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

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

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

#include "internal.h"

using namespace bssl;

// digest_to_scalar interprets |digest_len| bytes from |digest| as a scalar for

// ECDSA.

static void digest_to_scalar(const EC_GROUP *group, EC_SCALAR *out,

                             const uint8_t *digest, size_t digest_len) {

  const BIGNUM *order = EC_GROUP_get0_order(group);

  size_t num_bits = BN_num_bits(order);

  // Need to truncate digest if it is too long: first truncate whole bytes.

  size_t num_bytes = (num_bits + 7) / 8;

  if (digest_len > num_bytes) {

    digest_len = num_bytes;

  }

  bn_big_endian_to_words(out->words, order->width, digest, digest_len);

  // If it is still too long, truncate remaining bits with a shift.

  if (8 * digest_len > num_bits) {

    bn_rshift_words(out->words, out->words, 8 - (num_bits & 0x7), order->width);

  }

  // |out| now has the same bit width as |order|, but this only bounds by

  // 2*|order|. Subtract the order if out of range.

  //

  // Montgomery multiplication accepts the looser bounds, so this isn't strictly

  // necessary, but it is a cleaner abstraction and has no performance impact.

  BN_ULONG tmp[EC_MAX_WORDS];

  bn_reduce_once_in_place(out->words, 0 /* no carry */, order->d, tmp,

                          order->width);

}

int bssl::ecdsa_verify_fixed_no_self_test(const uint8_t *digest,

                                          size_t digest_len, const uint8_t *sig,

                                          size_t sig_len, const EC_KEY *eckey) {

  const EC_GROUP *group = EC_KEY_get0_group(eckey);

  const EC_POINT *pub_key = EC_KEY_get0_public_key(eckey);

  if (group == nullptr || pub_key == nullptr || sig == nullptr) {

    OPENSSL_PUT_ERROR(ECDSA, ECDSA_R_MISSING_PARAMETERS);

    return 0;

  }

  size_t scalar_len = BN_num_bytes(EC_GROUP_get0_order(group));

  EC_SCALAR r, s, u1, u2, s_inv_mont, m;

  if (sig_len != 2 * scalar_len ||

      !ec_scalar_from_bytes(group, &r, sig, scalar_len) ||

      ec_scalar_is_zero(group, &r) ||

      !ec_scalar_from_bytes(group, &s, sig + scalar_len, scalar_len) ||

      ec_scalar_is_zero(group, &s)) {

    OPENSSL_PUT_ERROR(ECDSA, ECDSA_R_BAD_SIGNATURE);

    return 0;

  }

  // s_inv_mont = s^-1 in the Montgomery domain.

  if (!ec_scalar_to_montgomery_inv_vartime(group, &s_inv_mont, &s)) {

    OPENSSL_PUT_ERROR(ECDSA, ERR_R_INTERNAL_ERROR);

    return 0;

  }

  // u1 = m * s^-1 mod order

  // u2 = r * s^-1 mod order

  //

  // |s_inv_mont| is in Montgomery form while |m| and |r| are not, so |u1| and

  // |u2| will be taken out of Montgomery form, as desired.

  digest_to_scalar(group, &m, digest, digest_len);

  ec_scalar_mul_montgomery(group, &u1, &m, &s_inv_mont);

  ec_scalar_mul_montgomery(group, &u2, &r, &s_inv_mont);

  EC_JACOBIAN point;

  if (!ec_point_mul_scalar_public(group, &point, &u1, &pub_key->raw, &u2)) {

    OPENSSL_PUT_ERROR(ECDSA, ERR_R_EC_LIB);

    return 0;

  }

  if (!ec_cmp_x_coordinate(group, &point, &r)) {

    OPENSSL_PUT_ERROR(ECDSA, ECDSA_R_BAD_SIGNATURE);

    return 0;

  }

  return 1;

}

int bssl::ecdsa_verify_fixed(const uint8_t *digest, size_t digest_len,

                             const uint8_t *sig, size_t sig_len,

                             const EC_KEY *key) {

  boringssl_ensure_ecc_self_test();

  return ecdsa_verify_fixed_no_self_test(digest, digest_len, sig, sig_len, key);

}

static int ecdsa_sign_impl(const EC_GROUP *group, int *out_retry, uint8_t *sig,

                           size_t *out_sig_len, size_t max_sig_len,

                           const EC_SCALAR *priv_key, const EC_SCALAR *k,

                           const uint8_t *digest, size_t digest_len) {

  *out_retry = 0;

  const BIGNUM *order = EC_GROUP_get0_order(group);

  size_t sig_len = 2 * BN_num_bytes(order);

  if (sig_len > max_sig_len) {

    OPENSSL_PUT_ERROR(EC, EC_R_BUFFER_TOO_SMALL);

    return 0;

  }

  // Compute r, the x-coordinate of k * generator.

  EC_JACOBIAN tmp_point;

  EC_SCALAR r;

  if (!ec_point_mul_scalar_base(group, &tmp_point, k) ||

      !ec_get_x_coordinate_as_scalar(group, &r, &tmp_point)) {

    return 0;

  }

  if (constant_time_declassify_int(ec_scalar_is_zero(group, &r))) {

    *out_retry = 1;

    return 0;

  }

  // s = priv_key * r. Note if only one parameter is in the Montgomery domain,

  // |ec_scalar_mod_mul_montgomery| will compute the answer in the normal

  // domain.

  EC_SCALAR s;

  ec_scalar_to_montgomery(group, &s, &r);

  ec_scalar_mul_montgomery(group, &s, priv_key, &s);

  // s = m + priv_key * r.

  EC_SCALAR tmp;

  digest_to_scalar(group, &tmp, digest, digest_len);

  ec_scalar_add(group, &s, &s, &tmp);

  // s = k^-1 * (m + priv_key * r). First, we compute k^-1 in the Montgomery

  // domain. This is |ec_scalar_to_montgomery| followed by

  // |ec_scalar_inv0_montgomery|, but |ec_scalar_inv0_montgomery| followed by

  // |ec_scalar_from_montgomery| is equivalent and slightly more efficient.

  // Then, as above, only one parameter is in the Montgomery domain, so the

  // result is in the normal domain. Finally, note k is non-zero (or computing r

  // would fail), so the inverse must exist.

  ec_scalar_inv0_montgomery(group, &tmp, k);     // tmp = k^-1 R^2

  ec_scalar_from_montgomery(group, &tmp, &tmp);  // tmp = k^-1 R

  ec_scalar_mul_montgomery(group, &s, &s, &tmp);

  if (constant_time_declassify_int(ec_scalar_is_zero(group, &s))) {

    *out_retry = 1;

    return 0;

  }

  CONSTTIME_DECLASSIFY(r.words, sizeof(r.words));

  CONSTTIME_DECLASSIFY(s.words, sizeof(r.words));

  size_t len;

  ec_scalar_to_bytes(group, sig, &len, &r);

  assert(len == sig_len / 2);

  ec_scalar_to_bytes(group, sig + len, &len, &s);

  assert(len == sig_len / 2);

  *out_sig_len = sig_len;

  return 1;

}

int bssl::ecdsa_sign_fixed_with_nonce_for_known_answer_test(

    const uint8_t *digest, size_t digest_len, uint8_t *sig, size_t *out_sig_len,

    size_t max_sig_len, const EC_KEY *eckey, const uint8_t *nonce,

    size_t nonce_len) {

  const ECKey *impl = FromOpaque(eckey);

  if (impl->ecdsa_meth && impl->ecdsa_meth->sign) {

    OPENSSL_PUT_ERROR(ECDSA, ECDSA_R_NOT_IMPLEMENTED);

    return 0;

  }

  const EC_GROUP *group = EC_KEY_get0_group(impl);

  if (group == nullptr || impl->priv_key == nullptr) {

    OPENSSL_PUT_ERROR(ECDSA, ERR_R_PASSED_NULL_PARAMETER);

    return 0;

  }

  const EC_SCALAR *priv_key = &impl->priv_key->scalar;

  EC_SCALAR k;

  if (!ec_scalar_from_bytes(group, &k, nonce, nonce_len)) {

    return 0;

  }

  int retry_ignored;

  return ecdsa_sign_impl(group, &retry_ignored, sig, out_sig_len, max_sig_len,

                         priv_key, &k, digest, digest_len);

}

int bssl::ecdsa_sign_fixed(const uint8_t *digest, size_t digest_len,

                           uint8_t *sig, size_t *out_sig_len,

                           size_t max_sig_len, const EC_KEY *eckey) {

  const ECKey *impl = FromOpaque(eckey);

  boringssl_ensure_ecc_self_test();

  if (impl->ecdsa_meth && impl->ecdsa_meth->sign) {

    OPENSSL_PUT_ERROR(ECDSA, ECDSA_R_NOT_IMPLEMENTED);

    return 0;

  }

  const EC_GROUP *group = EC_KEY_get0_group(impl);

  if (group == nullptr || impl->priv_key == nullptr) {

    OPENSSL_PUT_ERROR(ECDSA, ERR_R_PASSED_NULL_PARAMETER);

    return 0;

  }

  const BIGNUM *order = EC_GROUP_get0_order(group);

  const EC_SCALAR *priv_key = &impl->priv_key->scalar;

  // Generate the ECDSA per-message secret number by rejection sampling. This

  // function implements FIPS 186-5, A.3.2, repeating the process on failure.

  // Check the group order is large enough. See step 1 of FIPS 186-5, A.3.2.

  if (BN_num_bits(order) < 224) {

    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_GROUP_ORDER);

    return 0;

  }

  // Pass a SHA512 hash of the private key and digest as additional data

  // into the RBG. This is a hardening measure against entropy failure.

  static_assert(SHA512_DIGEST_LENGTH >= 32,

                "additional_data is too large for SHA-512");

  FIPS_service_indicator_lock_state();

  SHA512_CTX sha;

  uint8_t additional_data[SHA512_DIGEST_LENGTH];

  BCM_sha512_init(&sha);

  BCM_sha512_update(&sha, priv_key->words, order->width * sizeof(BN_ULONG));

  BCM_sha512_update(&sha, digest, digest_len);

  BCM_sha512_final(additional_data, &sha);

  // Cap iterations so callers who supply invalid values as custom groups do not

  // infinite loop. This does not impact valid parameters (e.g. those covered by

  // FIPS) because the probability of requiring even one retry is negligible,

  // let alone 32.

  static const int kMaxIterations = 32;

  int ret = 0;

  int iters = 0;

  for (;;) {

    EC_SCALAR k;

    if (!ec_random_nonzero_scalar(group, &k, additional_data)) {

      goto out;

    }

    // TODO(davidben): Move this inside |ec_random_nonzero_scalar| or lower, so

    // that all scalars we generate are, by default, secret.

    CONSTTIME_SECRET(k.words, sizeof(k.words));

    int retry;

    ret = ecdsa_sign_impl(group, &retry, sig, out_sig_len, max_sig_len,

                          priv_key, &k, digest, digest_len);

    if (ret || !retry) {

      goto out;

    }

    iters++;

    if (iters > kMaxIterations) {

      OPENSSL_PUT_ERROR(ECDSA, ECDSA_R_TOO_MANY_ITERATIONS);

      goto out;

    }

  }

out:

  FIPS_service_indicator_unlock_state();

  return ret;

}