// Copyright 2024 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/base.h>

#include <assert.h>

#include <string.h>

#include <openssl/bn.h>

#include <openssl/bytestring.h>

#include <openssl/crypto.h>

#include <openssl/ec.h>

#include <openssl/err.h>

#include <openssl/evp.h>

#include <openssl/hkdf.h>

#include <openssl/hmac.h>

#include <openssl/mem.h>

#include <openssl/rand.h>

#include <openssl/sha.h>

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

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

#include "../internal.h"

#include "./internal.h"

BSSL_NAMESPACE_BEGIN

namespace spake2plus {

namespace {

const uint8_t kDefaultAdditionalData[32] = {0};

// https://www.rfc-editor.org/rfc/rfc9383.html#appendix-B

// seed: 1.2.840.10045.3.1.7 point generation seed (M)

// M =

// 02886e2f97ace46e55ba9dd7242579f2993b64e16ef3dcab95afd497333d8fa12f

//

// `M` is interpreted as a X9.62-format compressed point. This is then the

// uncompressed form:

const uint8_t kM_bytes[] = {

    0x04, 0x88, 0x6e, 0x2f, 0x97, 0xac, 0xe4, 0x6e, 0x55, 0xba, 0x9d,

    0xd7, 0x24, 0x25, 0x79, 0xf2, 0x99, 0x3b, 0x64, 0xe1, 0x6e, 0xf3,

    0xdc, 0xab, 0x95, 0xaf, 0xd4, 0x97, 0x33, 0x3d, 0x8f, 0xa1, 0x2f,

    0x5f, 0xf3, 0x55, 0x16, 0x3e, 0x43, 0xce, 0x22, 0x4e, 0x0b, 0x0e,

    0x65, 0xff, 0x02, 0xac, 0x8e, 0x5c, 0x7b, 0xe0, 0x94, 0x19, 0xc7,

    0x85, 0xe0, 0xca, 0x54, 0x7d, 0x55, 0xa1, 0x2e, 0x2d, 0x20};

// https://www.rfc-editor.org/rfc/rfc9383.html#appendix-B

// seed: 1.2.840.10045.3.1.7 point generation seed (N)

// N =

// 03d8bbd6c639c62937b04d997f38c3770719c629d7014d49a24b4f98baa1292b49

//

// `N` is interpreted as a X9.62-format compressed point. This is then the

// uncompressed form:

const uint8_t kN_bytes[] = {

    0x04, 0xd8, 0xbb, 0xd6, 0xc6, 0x39, 0xc6, 0x29, 0x37, 0xb0, 0x4d,

    0x99, 0x7f, 0x38, 0xc3, 0x77, 0x07, 0x19, 0xc6, 0x29, 0xd7, 0x01,

    0x4d, 0x49, 0xa2, 0x4b, 0x4f, 0x98, 0xba, 0xa1, 0x29, 0x2b, 0x49,

    0x07, 0xd6, 0x0a, 0xa6, 0xbf, 0xad, 0xe4, 0x50, 0x08, 0xa6, 0x36,

    0x33, 0x7f, 0x51, 0x68, 0xc6, 0x4d, 0x9b, 0xd3, 0x60, 0x34, 0x80,

    0x8c, 0xd5, 0x64, 0x49, 0x0b, 0x1e, 0x65, 0x6e, 0xdb, 0xe7};

void UpdateWithLengthPrefix(SHA256_CTX *sha, Span<const uint8_t> data) {

  uint8_t len_le[8];

  CRYPTO_store_u64_le(len_le, data.size());

  SHA256_Update(sha, len_le, sizeof(len_le));

  SHA256_Update(sha, data.data(), data.size());

}

void ConstantToJacobian(const EC_GROUP *group, EC_JACOBIAN *out,

                        bssl::Span<const uint8_t> in) {

  EC_AFFINE point;

  BSSL_CHECK(ec_point_from_uncompressed(group, &point, in.data(), in.size()));

  ec_affine_to_jacobian(group, out, &point);

}

void ScalarToSizedBuffer(const EC_GROUP *group, const EC_SCALAR *s,

                         Span<uint8_t> out_buf) {

  size_t out_bytes;

  ec_scalar_to_bytes(group, out_buf.data(), &out_bytes, s);

  BSSL_CHECK(out_bytes == out_buf.size());

}

bool AddLengthPrefixed(CBB *cbb, Span<const uint8_t> bytes) {

  return CBB_add_u64le(cbb, bytes.size()) &&

         CBB_add_bytes(cbb, bytes.data(), bytes.size());

}

void InitTranscriptHash(SHA256_CTX *sha, Span<const uint8_t> context,

                        Span<const uint8_t> id_prover,

                        Span<const uint8_t> id_verifier) {

  SHA256_Init(sha);

  UpdateWithLengthPrefix(sha, context);

  UpdateWithLengthPrefix(sha, id_prover);

  UpdateWithLengthPrefix(sha, id_verifier);

  UpdateWithLengthPrefix(sha, kM_bytes);

  UpdateWithLengthPrefix(sha, kN_bytes);

}

bool ComputeTranscript(uint8_t out_prover_confirm[kConfirmSize],

                       uint8_t out_verifier_confirm[kConfirmSize],

                       uint8_t out_secret[kSecretSize],

                       const uint8_t prover_share[kShareSize],

                       const uint8_t verifier_share[kShareSize],

                       SHA256_CTX *sha, const EC_AFFINE *Z, const EC_AFFINE *V,

                       const EC_SCALAR *w0) {

  const EC_GROUP *group = EC_group_p256();

  uint8_t Z_enc[kShareSize];

  size_t Z_enc_len = ec_point_to_bytes(group, Z, POINT_CONVERSION_UNCOMPRESSED,

                                       Z_enc, sizeof(Z_enc));

  BSSL_CHECK(Z_enc_len == sizeof(Z_enc));

  uint8_t V_enc[kShareSize];

  size_t V_enc_len = ec_point_to_bytes(group, V, POINT_CONVERSION_UNCOMPRESSED,

                                       V_enc, sizeof(V_enc));

  BSSL_CHECK(V_enc_len == sizeof(V_enc));

  uint8_t w0_enc[kVerifierSize];

  ScalarToSizedBuffer(group, w0, w0_enc);

  uint8_t K_main[SHA256_DIGEST_LENGTH];

  UpdateWithLengthPrefix(sha, Span(prover_share, kShareSize));

  UpdateWithLengthPrefix(sha, Span(verifier_share, kShareSize));

  UpdateWithLengthPrefix(sha, Z_enc);

  UpdateWithLengthPrefix(sha, V_enc);

  UpdateWithLengthPrefix(sha, w0_enc);

  SHA256_Final(K_main, sha);

  auto confirmation_str = StringAsBytes("ConfirmationKeys");

  uint8_t keys[kSecretSize * 2];

  if (!HKDF(keys, sizeof(keys), EVP_sha256(), K_main, sizeof(K_main), nullptr,

            0, confirmation_str.data(), confirmation_str.size())) {

    return false;

  }

  auto secret_info_str = StringAsBytes("SharedKey");

  if (!HKDF(out_secret, kSecretSize, EVP_sha256(), K_main, sizeof(K_main),

            nullptr, 0, secret_info_str.data(), secret_info_str.size())) {

    return false;

  }

  unsigned prover_confirm_len;

  if (HMAC(EVP_sha256(), keys, kSecretSize, verifier_share, kShareSize,

           out_prover_confirm, &prover_confirm_len) == nullptr) {

    return false;

  }

  BSSL_CHECK(prover_confirm_len == kConfirmSize);

  unsigned verifier_confirm_len;

  if (HMAC(EVP_sha256(), keys + kSecretSize, kSecretSize, prover_share,

           kShareSize, out_verifier_confirm,

           &verifier_confirm_len) == nullptr) {

    return false;

  }

  BSSL_CHECK(verifier_confirm_len == kConfirmSize);

  return true;

}

}  // namespace

bool Register(Span<uint8_t> out_w0, Span<uint8_t> out_w1,

              Span<uint8_t> out_registration_record,

              Span<const uint8_t> password, Span<const uint8_t> id_prover,

              Span<const uint8_t> id_verifier) {

  if (out_w0.size() != kVerifierSize || out_w1.size() != kVerifierSize ||

      out_registration_record.size() != kRegistrationRecordSize) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  // Offline registration format from:

  // https://www.rfc-editor.org/rfc/rfc9383.html#section-3.2

  ScopedCBB mhf_input;

  if (!CBB_init(mhf_input.get(), password.size() + id_prover.size() +

                                     id_verifier.size() +

                                     3 * sizeof(uint64_t)) ||  //

      !AddLengthPrefixed(mhf_input.get(), password) ||

      !AddLengthPrefixed(mhf_input.get(), id_prover) ||

      !AddLengthPrefixed(mhf_input.get(), id_verifier) ||

      !CBB_flush(mhf_input.get())) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  // https://neuromancer.sk/std/nist/P-256

  //   sage: p =

  //   0xffffffff00000001000000000000000000000000ffffffffffffffffffffffff

  //   ....: K = GF(p)

  //   ....: a =

  //   K(0xffffffff00000001000000000000000000000000fffffffffffffffffffffffc)

  //   ....: b =

  //   K(0x5ac635d8aa3a93e7b3ebbd55769886bc651d06b0cc53b0f63bce3c3e27d2604b)

  //   ....: E = EllipticCurve(K, (a, b))

  //   ....: G =

  //   E(0x6b17d1f2e12c4247f8bce6e563a440f277037d812deb33a0f4a13945d898c296,

  //   ....: 0x4fe342e2fe1a7f9b8ee7eb4a7c0f9e162bce33576b315ececbb6406837bf51f5)

  //   ....:

  //   E.set_order(0xffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc63

  //   ....: 2551 * 0x1)

  //   sage: k = 64

  //   sage: L = (2 * (ceil(log(p)/log(2)) + k)) / 8

  // RFC 9383 Section 3.2

  constexpr size_t kKDFOutputSize = 80;

  constexpr size_t kKDFOutputWords = kKDFOutputSize / BN_BYTES;

  uint8_t key[kKDFOutputSize];

  if (!EVP_PBE_scrypt((const char *)CBB_data(mhf_input.get()),

                      CBB_len(mhf_input.get()), nullptr, 0,

                      /*N=*/32768, /*r=*/8, /*p=*/1,

                      /*max_mem=*/1024 * 1024 * 33, key, kKDFOutputSize)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  const EC_GROUP *group = EC_group_p256();

  BN_ULONG w0_words[kKDFOutputWords / 2];

  bn_big_endian_to_words(w0_words, kKDFOutputWords / 2, key,

                         kKDFOutputSize / 2);

  EC_SCALAR w0;

  ec_scalar_reduce(group, &w0, w0_words, kKDFOutputWords / 2);

  ScalarToSizedBuffer(group, &w0, out_w0);

  BN_ULONG w1_words[kKDFOutputWords / 2];

  bn_big_endian_to_words(w1_words, kKDFOutputWords / 2,

                         key + kKDFOutputSize / 2, kKDFOutputSize / 2);

  EC_SCALAR w1;

  ec_scalar_reduce(group, &w1, w1_words, kKDFOutputWords / 2);

  ScalarToSizedBuffer(group, &w1, out_w1);

  EC_JACOBIAN L_j;

  EC_AFFINE L;

  if (!ec_point_mul_scalar_base(group, &L_j, &w1) ||  //

      !ec_jacobian_to_affine(group, &L, &L_j) ||      //

      !ec_point_to_bytes(group, &L, POINT_CONVERSION_UNCOMPRESSED,

                         out_registration_record.data(),

                         kRegistrationRecordSize)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  return true;

}

Prover::Prover() = default;

Prover::~Prover() = default;

bool Prover::Init(Span<const uint8_t> context, Span<const uint8_t> id_prover,

                  Span<const uint8_t> id_verifier, Span<const uint8_t> w0,

                  Span<const uint8_t> w1, Span<const uint8_t> x) {

  const EC_GROUP *group = EC_group_p256();

  if (!ec_scalar_from_bytes(group, &w0_, w0.data(), w0.size()) ||

      !ec_scalar_from_bytes(group, &w1_, w1.data(), w1.size()) ||

      (!x.empty() &&

       !ec_scalar_from_bytes(group, &x_, x.data(), x.size())) ||  //

      (x.empty() && !ec_random_scalar(group, &x_, kDefaultAdditionalData))) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  InitTranscriptHash(&transcript_hash_, context, id_prover, id_verifier);

  return true;

}

bool Prover::GenerateShare(Span<uint8_t> out_share) {

  if (state_ != State::kInit || out_share.size() != kShareSize) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  // Compute X = x×P + w0×M.

  // TODO(crbug.com/383778231): This could be sped up with a constant-time,

  // two-point multiplication.

  const EC_GROUP *group = EC_group_p256();

  EC_JACOBIAN l;

  if (!ec_point_mul_scalar_base(group, &l, &x_)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  EC_JACOBIAN M_j;

  ConstantToJacobian(group, &M_j, kM_bytes);

  EC_JACOBIAN r;

  if (!ec_point_mul_scalar(group, &r, &M_j, &w0_)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  EC_JACOBIAN X_j;

  group->meth->add(group, &X_j, &l, &r);

  if (!ec_jacobian_to_affine(group, &X_, &X_j)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  size_t written = ec_point_to_bytes(group, &X_, POINT_CONVERSION_UNCOMPRESSED,

                                     out_share.data(), kShareSize);

  BSSL_CHECK(written == kShareSize);

  memcpy(share_, out_share.data(), kShareSize);

  state_ = State::kShareGenerated;

  return true;

}

bool Prover::ComputeConfirmation(Span<uint8_t> out_confirm,

                                 Span<uint8_t> out_secret,

                                 Span<const uint8_t> peer_share,

                                 Span<const uint8_t> peer_confirm) {

  if (state_ != State::kShareGenerated || out_confirm.size() != kConfirmSize ||

      out_secret.size() != kSecretSize || peer_share.size() != kShareSize ||

      peer_confirm.size() != kConfirmSize) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  const EC_GROUP *group = EC_group_p256();

  EC_AFFINE Y;

  if (!ec_point_from_uncompressed(group, &Y, peer_share.data(),

                                  peer_share.size())) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  EC_JACOBIAN N_j;

  ConstantToJacobian(group, &N_j, kN_bytes);

  EC_JACOBIAN r;

  if (!ec_point_mul_scalar(group, &r, &N_j, &w0_)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  ec_felem_neg(group, &r.Y, &r.Y);

  EC_JACOBIAN Y_j;

  ec_affine_to_jacobian(group, &Y_j, &Y);

  EC_JACOBIAN t;

  group->meth->add(group, &t, &Y_j, &r);

  EC_JACOBIAN tmp;

  EC_AFFINE Z, V;

  // TODO(crbug.com/383778231): The two affine conversions could be batched

  // together.

  if (!ec_point_mul_scalar(group, &tmp, &t, &x_) ||   //

      !ec_jacobian_to_affine(group, &Z, &tmp) ||      //

      !ec_point_mul_scalar(group, &tmp, &t, &w1_) ||  //

      !ec_jacobian_to_affine(group, &V, &tmp)) {

    return 0;

  }

  uint8_t verifier_confirm[kConfirmSize];

  if (!ComputeTranscript(out_confirm.data(), verifier_confirm,

                         out_secret.data(), share_, peer_share.data(),

                         &transcript_hash_, &Z, &V, &w0_) ||

      CRYPTO_memcmp(verifier_confirm, peer_confirm.data(),

                    sizeof(verifier_confirm)) != 0) {

    return 0;

  }

  state_ = State::kDone;

  return true;

}

Verifier::Verifier() = default;

Verifier::~Verifier() = default;

bool Verifier::Init(Span<const uint8_t> context, Span<const uint8_t> id_prover,

                    Span<const uint8_t> id_verifier, Span<const uint8_t> w0,

                    Span<const uint8_t> registration_record,

                    Span<const uint8_t> y) {

  const EC_GROUP *group = EC_group_p256();

  if (!ec_scalar_from_bytes(group, &w0_, w0.data(), w0.size()) ||

      !ec_point_from_uncompressed(group, &L_, registration_record.data(),

                                  registration_record.size()) ||  //

      (!y.empty() &&

       !ec_scalar_from_bytes(group, &y_, y.data(), y.size())) ||  //

      (y.empty() && !ec_random_scalar(group, &y_, kDefaultAdditionalData))) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  InitTranscriptHash(&transcript_hash_, context, id_prover, id_verifier);

  return true;

}

bool Verifier::ProcessProverShare(Span<uint8_t> out_share,

                                  Span<uint8_t> out_confirm,

                                  Span<uint8_t> out_secret,

                                  Span<const uint8_t> prover_share) {

  if (state_ != State::kInit ||  //

      out_share.size() != kShareSize || out_confirm.size() != kConfirmSize ||

      out_secret.size() != kSecretSize || prover_share.size() != kShareSize) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  const EC_GROUP *group = EC_group_p256();

  EC_JACOBIAN l, r, M_j, N_j;

  ConstantToJacobian(group, &M_j, kM_bytes);

  ConstantToJacobian(group, &N_j, kN_bytes);

  // Compute Y = y×P + w0×M.

  // TODO(crbug.com/383778231): This could be sped up with a constant-time,

  // two-point multiplication.

  if (!ec_point_mul_scalar_base(group, &l, &y_) ||

      !ec_point_mul_scalar(group, &r, &N_j, &w0_)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  EC_JACOBIAN Y_j;

  EC_AFFINE Y;

  group->meth->add(group, &Y_j, &l, &r);

  if (!ec_jacobian_to_affine(group, &Y, &Y_j)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  const size_t written = ec_point_to_bytes(

      group, &Y, POINT_CONVERSION_UNCOMPRESSED, out_share.data(), kShareSize);

  BSSL_CHECK(written == kShareSize);

  EC_JACOBIAN r2;

  EC_AFFINE X;

  if (!ec_point_from_uncompressed(group, &X, prover_share.data(),

                                  prover_share.size()) ||

      !ec_point_mul_scalar(group, &r2, &M_j, &w0_)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  ec_felem_neg(group, &r2.Y, &r2.Y);

  EC_JACOBIAN X_j, T;

  ec_affine_to_jacobian(group, &X_j, &X);

  group->meth->add(group, &T, &X_j, &r2);

  // TODO(crbug.com/383778231): The two affine conversions could be batched

  // together.

  EC_JACOBIAN tmp;

  EC_AFFINE Z;

  if (!ec_point_mul_scalar(group, &tmp, &T, &y_) ||  //

      !ec_jacobian_to_affine(group, &Z, &tmp)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  EC_JACOBIAN L_j;

  EC_AFFINE V;

  ec_affine_to_jacobian(group, &L_j, &L_);

  if (!ec_point_mul_scalar(group, &tmp, &L_j, &y_) ||  //

      !ec_jacobian_to_affine(group, &V, &tmp)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  if (!ComputeTranscript(confirm_, out_confirm.data(), out_secret.data(),

                         prover_share.data(), out_share.data(),

                         &transcript_hash_, &Z, &V, &w0_)) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  state_ = State::kProverShareSeen;

  return true;

}

bool Verifier::VerifyProverConfirmation(Span<const uint8_t> peer_confirm) {

  if (state_ != State::kProverShareSeen ||    //

      peer_confirm.size() != kConfirmSize ||  //

      CRYPTO_memcmp(confirm_, peer_confirm.data(), sizeof(confirm_)) != 0) {

    OPENSSL_PUT_ERROR(CRYPTO, ERR_R_INTERNAL_ERROR);

    return false;

  }

  state_ = State::kDone;

  return true;

}

}  // namespace spake2plus

BSSL_NAMESPACE_END