// Copyright (c) 2014-2017 Thomas Fussell
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, WRISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE
//
// @license: http://www.opensource.org/licenses/mit-license.php
// @author: see AUTHORS file

#include <detail/xlsx_crypto.hpp>

namespace {

template <typename T>
auto read_int(std::size_t &index, const std::vector<std::uint8_t> &raw_data)
{
    auto result = *reinterpret_cast<const T *>(&raw_data[index]);
    index += sizeof(T);

    return result;
}

} // namespace

namespace xml {

template <>
struct value_traits<xlnt::detail::hash_algorithm>
{
    static xlnt::detail::hash_algorithm parse(std::string hash_algorithm_string, const parser &)
    {
        if (hash_algorithm_string == "SHA1")
            return xlnt::detail::hash_algorithm::sha1;
        else if (hash_algorithm_string == "SHA256")
            return xlnt::detail::hash_algorithm::sha256;
        else if (hash_algorithm_string == "SHA384")
            return xlnt::detail::hash_algorithm::sha384;
        else if (hash_algorithm_string == "SHA512")
            return xlnt::detail::hash_algorithm::sha512;
        else if (hash_algorithm_string == "MD5")
            return xlnt::detail::hash_algorithm::md5;
        else if (hash_algorithm_string == "MD4")
            return xlnt::detail::hash_algorithm::md4;
        else if (hash_algorithm_string == "MD2")
            return xlnt::detail::hash_algorithm::md2;
        else if (hash_algorithm_string == "Ripemd128")
            return xlnt::detail::hash_algorithm::ripemd128;
        else if (hash_algorithm_string == "Ripemd160")
            return xlnt::detail::hash_algorithm::ripemd160;
        else if (hash_algorithm_string == "Whirlpool")
            return xlnt::detail::hash_algorithm::whirlpool;
        throw xlnt::exception(hash_algorithm_string);
    }

    static std::string serialize(xlnt::detail::hash_algorithm algorithm, const serializer &)
    {
        switch (algorithm)
        {
        case xlnt::detail::hash_algorithm::sha1:
            return "SHA1";
        case xlnt::detail::hash_algorithm::sha256:
            return "SHA256";
        case xlnt::detail::hash_algorithm::sha384:
            return "SHA384";
        case xlnt::detail::hash_algorithm::sha512:
            return "SHA512";
        case xlnt::detail::hash_algorithm::md5:
            return "MD5";
        case xlnt::detail::hash_algorithm::md4:
            return "MD4";
        case xlnt::detail::hash_algorithm::md2:
            return "MD2";
        case xlnt::detail::hash_algorithm::ripemd128:
            return "Ripemd128";
        case xlnt::detail::hash_algorithm::ripemd160:
            return "Ripemd160";
        case xlnt::detail::hash_algorithm::whirlpool:
            return "Whirlpool";
        }
    }
}; // struct value_traits<>

} // namespace xml

namespace xlnt {
namespace detail {

std::vector<std::uint8_t> crypto_helper::aes(
    const std::vector<std::uint8_t> &key,
    const std::vector<std::uint8_t> &iv,
    const std::vector<std::uint8_t> &source,
    cipher_chaining chaining, cipher_direction direction)
{
    std::vector<std::uint8_t> destination(source.size(), 0);

    if (direction == cipher_direction::encryption && chaining == cipher_chaining::cbc)
    {
        CryptoPP::AES::Encryption aesEncryption(key.data(), key.size());
        CryptoPP::CBC_Mode_ExternalCipher::Encryption cbcEncryption(aesEncryption, iv.data());

        CryptoPP::ArraySource as(
            source.data(), source.size(), true, new CryptoPP::StreamTransformationFilter(cbcEncryption,
                                                    new CryptoPP::ArraySink(destination.data(), destination.size()),
                                                    CryptoPP::BlockPaddingSchemeDef::NO_PADDING));
    }
    else if (direction == cipher_direction::decryption && chaining == cipher_chaining::cbc)
    {
        CryptoPP::AES::Decryption aesDecryption(key.data(), key.size());
        CryptoPP::CBC_Mode_ExternalCipher::Decryption cbcDecryption(aesDecryption, iv.data());

        CryptoPP::ArraySource as(
            source.data(), source.size(), true, new CryptoPP::StreamTransformationFilter(cbcDecryption,
                                                    new CryptoPP::ArraySink(destination.data(), destination.size()),
                                                    CryptoPP::BlockPaddingSchemeDef::NO_PADDING));
    }
    else if (direction == cipher_direction::encryption && chaining == cipher_chaining::ecb)
    {
        CryptoPP::AES::Encryption aesEncryption(key.data(), key.size());
        CryptoPP::ECB_Mode_ExternalCipher::Encryption cbcEncryption(aesEncryption, iv.data());

        CryptoPP::ArraySource as(
            source.data(), source.size(), true, new CryptoPP::StreamTransformationFilter(cbcEncryption,
                                                    new CryptoPP::ArraySink(destination.data(), destination.size()),
                                                    CryptoPP::BlockPaddingSchemeDef::NO_PADDING));
    }
    else if (direction == cipher_direction::decryption && chaining == cipher_chaining::ecb)
    {
        CryptoPP::AES::Decryption aesDecryption(key.data(), key.size());
        CryptoPP::ECB_Mode_ExternalCipher::Decryption cbcDecryption(aesDecryption, iv.data());

        CryptoPP::ArraySource as(
            source.data(), source.size(), true, new CryptoPP::StreamTransformationFilter(cbcDecryption,
                                                    new CryptoPP::ArraySink(destination.data(), destination.size()),
                                                    CryptoPP::BlockPaddingSchemeDef::NO_PADDING));
    }

    return destination;
}

std::vector<std::uint8_t> crypto_helper::decode_base64(const std::string &encoded)
{
    CryptoPP::Base64Decoder decoder;
    decoder.Put(reinterpret_cast<const std::uint8_t *>(encoded.data()), encoded.size());
    decoder.MessageEnd();

    std::vector<std::uint8_t> decoded(decoder.MaxRetrievable(), 0);
    decoder.Get(decoded.data(), decoded.size());

    return decoded;
}

std::string crypto_helper::encode_base64(const std::vector<std::uint8_t> &decoded)
{
    CryptoPP::Base64Decoder encoder;
    encoder.Put(reinterpret_cast<const std::uint8_t *>(decoded.data()), decoded.size());
    encoder.MessageEnd();

    std::vector<std::uint8_t> encoded(encoder.MaxRetrievable(), 0);
    encoder.Get(encoded.data(), encoded.size());

    return std::string(encoded.begin(), encoded.end());
}

std::vector<std::uint8_t> crypto_helper::hash(hash_algorithm algorithm, const std::vector<std::uint8_t> &input)
{
    std::vector<std::uint8_t> digest;

    if (algorithm == hash_algorithm::sha512)
    {
        CryptoPP::SHA512 sha512;
        digest.resize(CryptoPP::SHA512::DIGESTSIZE, 0);
        sha512.CalculateDigest(digest.data(), input.data(), input.size());
    }
    else if (algorithm == hash_algorithm::sha1)
    {
        CryptoPP::SHA1 sha1;
        digest.resize(CryptoPP::SHA1::DIGESTSIZE, 0);
        sha1.CalculateDigest(digest.data(), input.data(), input.size());
    }

    return digest;
}

std::vector<std::uint8_t> crypto_helper::file(POLE::Storage &storage, const std::string &name)
{
    POLE::Stream stream(&storage, name.c_str());
    if (stream.fail()) return {};
    std::vector<std::uint8_t> bytes(stream.size(), 0);
    stream.read(bytes.data(), static_cast<unsigned long>(bytes.size()));
    return bytes;
}

std::vector<std::uint8_t> crypto_helper::decrypt_xlsx_standard(
    const std::vector<std::uint8_t> &encryption_info,
    const std::string &password,
    const std::vector<std::uint8_t> &encrypted_package)
{
    std::size_t offset = 0;

    standard_encryption_info info;

    auto header_length = read_int<std::uint32_t>(offset, encryption_info);
    auto index_at_start = offset;
    /*auto skip_flags = */ read_int<std::uint32_t>(offset, encryption_info);
    /*auto size_extra = */ read_int<std::uint32_t>(offset, encryption_info);
    auto alg_id = read_int<std::uint32_t>(offset, encryption_info);

    if (alg_id == 0 || alg_id == 0x0000660E || alg_id == 0x0000660F || alg_id == 0x00006610)
    {
        info.cipher = cipher_algorithm::aes;
    }
    else
    {
        throw xlnt::exception("invalid cipher algorithm");
    }

    auto alg_id_hash = read_int<std::uint32_t>(offset, encryption_info);
    if (alg_id_hash != 0x00008004 && alg_id_hash == 0)
    {
        throw xlnt::exception("invalid hash algorithm");
    }

    info.key_bits = read_int<std::uint32_t>(offset, encryption_info);
    info.key_bytes = info.key_bits / 8;

    auto provider_type = read_int<std::uint32_t>(offset, encryption_info);
    if (provider_type != 0 && provider_type != 0x00000018)
    {
        throw xlnt::exception("invalid provider type");
    }

    read_int<std::uint32_t>(offset, encryption_info); // reserved 1
    if (read_int<std::uint32_t>(offset, encryption_info) != 0) // reserved 2
    {
        throw xlnt::exception("invalid header");
    }

    const auto csp_name_length = header_length - (offset - index_at_start);
    std::vector<std::uint16_t> csp_name_wide(
        reinterpret_cast<const std::uint16_t *>(&*(encryption_info.begin() + static_cast<std::ptrdiff_t>(offset))),
        reinterpret_cast<const std::uint16_t *>(
            &*(encryption_info.begin() + static_cast<std::ptrdiff_t>(offset + csp_name_length))));
    std::string csp_name(csp_name_wide.begin(), csp_name_wide.end() - 1); // without trailing null
    if (csp_name != "Microsoft Enhanced RSA and AES Cryptographic Provider (Prototype)"
        && csp_name != "Microsoft Enhanced RSA and AES Cryptographic Provider")
    {
        throw xlnt::exception("invalid cryptographic provider");
    }
    offset += csp_name_length;

    const auto salt_size = read_int<std::uint32_t>(offset, encryption_info);
    std::vector<std::uint8_t> salt(encryption_info.begin() + static_cast<std::ptrdiff_t>(offset),
        encryption_info.begin() + static_cast<std::ptrdiff_t>(offset + salt_size));
    offset += salt_size;

    static const auto verifier_size = std::size_t(16);
    std::vector<std::uint8_t> verifier_hash_input(encryption_info.begin() + static_cast<std::ptrdiff_t>(offset),
        encryption_info.begin() + static_cast<std::ptrdiff_t>(offset + verifier_size));
    offset += verifier_size;

    const auto verifier_hash_size = read_int<std::uint32_t>(offset, encryption_info);
    std::vector<std::uint8_t> verifier_hash_value(encryption_info.begin() + static_cast<std::ptrdiff_t>(offset),
        encryption_info.begin() + static_cast<std::ptrdiff_t>(offset + verifier_hash_size));
    offset += verifier_hash_size;

    // begin key generation algorithm

    // H_0 = H(salt + password)
    auto salt_plus_password = salt;
    std::vector<std::uint16_t> password_wide(password.begin(), password.end());
    std::for_each(password_wide.begin(), password_wide.end(), [&salt_plus_password](std::uint16_t c) {
        salt_plus_password.insert(salt_plus_password.end(), reinterpret_cast<char *>(&c),
            reinterpret_cast<char *>(&c) + sizeof(std::uint16_t));
    });
    std::vector<std::uint8_t> h_0 = hash(info.hash, salt_plus_password);

    // H_n = H(iterator + H_n-1)
    std::vector<std::uint8_t> iterator_plus_h_n(4, 0);
    iterator_plus_h_n.insert(iterator_plus_h_n.end(), h_0.begin(), h_0.end());
    std::uint32_t &iterator = *reinterpret_cast<std::uint32_t *>(iterator_plus_h_n.data());
    std::vector<std::uint8_t> h_n;
    for (iterator = 0; iterator < info.spin_count; ++iterator)
    {
        h_n = hash(info.hash, iterator_plus_h_n);
        std::copy(h_n.begin(), h_n.end(), iterator_plus_h_n.begin() + 4);
    }

    // H_final = H(H_n + block)
    auto h_n_plus_block = h_n;
    const std::uint32_t block_number = 0;
    h_n_plus_block.insert(h_n_plus_block.end(), reinterpret_cast<const std::uint8_t *>(&block_number),
        reinterpret_cast<const std::uint8_t *>(&block_number) + sizeof(std::uint32_t));
    auto h_final = hash(info.hash, h_n_plus_block);

    // X1 = H(h_final ^ 0x36)
    std::vector<std::uint8_t> buffer(64, 0x36);
    for (std::size_t i = 0; i < h_final.size(); ++i)
    {
        buffer[i] = static_cast<std::uint8_t>(0x36 ^ h_final[i]);
    }
    auto X1 = hash(info.hash, buffer);

    // X2 = H(h_final ^ 0x5C)
    buffer.assign(64, 0x5c);
    for (std::size_t i = 0; i < h_final.size(); ++i)
    {
        buffer[i] = static_cast<std::uint8_t>(0x5c ^ h_final[i]);
    }
    auto X2 = hash(info.hash, buffer);

    auto X3 = X1;
    X3.insert(X3.end(), X2.begin(), X2.end());

    auto key_derived =
        std::vector<std::uint8_t>(X3.begin(), X3.begin() + static_cast<std::ptrdiff_t>(info.key_bytes));

    // todo: verify here

    std::size_t package_offset = 0;
    auto decrypted_size = static_cast<std::size_t>(read_int<std::uint64_t>(package_offset, encrypted_package));
    auto decrypted = aes(key_derived, {},
        std::vector<std::uint8_t>(encrypted_package.begin() + 8, encrypted_package.end()),
        cipher_chaining::ecb, cipher_direction::decryption);
    decrypted.resize(decrypted_size);

    return decrypted;
}

crypto_helper::agile_encryption_info crypto_helper::generate_agile_encryption_info(const std::string &password)
{
    agile_encryption_info result;
    result.key_data.salt_value.assign(password.begin(), password.end());
    return result;
}

std::vector<std::uint8_t> crypto_helper::write_agile_encryption_info(const std::string &password)
{
    static const auto &xmlns = xlnt::constants::ns("encryption");
    static const auto &xmlns_p = xlnt::constants::ns("encryption-password");

    std::vector<std::uint8_t> encryption_info;
    xlnt::detail::vector_ostreambuf encryption_info_buffer(encryption_info);
    std::ostream encryption_info_stream(&encryption_info_buffer);
    xml::serializer serializer(encryption_info_stream, "EncryptionInfo");

    agile_encryption_info result = generate_agile_encryption_info(password);

    serializer.start_element(xmlns, "encryption");

    serializer.start_element(xmlns, "keyData");
    serializer.attribute("saltSize", result.key_data.salt_size);
    serializer.attribute("blockSize", result.key_data.block_size);
    serializer.attribute("keyBits", result.key_data.key_bits);
    serializer.attribute("hashSize", result.key_data.hash_size);
    serializer.attribute("cipherAlgorithm", result.key_data.cipher_algorithm);
    serializer.attribute("cipherChaining", result.key_data.cipher_chaining);
    serializer.attribute("hashAlgorithm", result.key_data.hash_algorithm);
    serializer.attribute("saltValue", encode_base64(result.key_data.salt_value));
    serializer.end_element(xmlns, "keyData");

    serializer.start_element(xmlns, "dataIntegrity");
    serializer.attribute("encryptedHmacKey", encode_base64(result.data_integrity.hmac_key));
    serializer.attribute("encryptedHmacValue", encode_base64(result.data_integrity.hmac_value));
    serializer.end_element(xmlns, "dataIntegrity");

    serializer.start_element(xmlns, "keyEncryptors");
    serializer.start_element(xmlns, "keyEncryptor");
    serializer.attribute("uri", "");
    serializer.start_element(xmlns_p, "encryptedKey");
    serializer.attribute("spinCount", result.key_encryptor.spin_count);
    serializer.attribute("saltSize", result.key_encryptor.salt_size);
    serializer.attribute("blockSize", result.key_encryptor.block_size);
    serializer.attribute("keyBits", result.key_encryptor.key_bits);
    serializer.attribute("hashSize", result.key_encryptor.hash_size);
    serializer.attribute("cipherAlgorithm", result.key_encryptor.cipher_algorithm);
    serializer.attribute("cipherChaining", result.key_encryptor.cipher_chaining);
    serializer.attribute("hashAlgorithm", result.key_encryptor.hash);
    serializer.attribute("saltValue", encode_base64(result.key_encryptor.salt_value));
    serializer.attribute("encryptedVerifierHashInput", encode_base64(result.key_encryptor.verifier_hash_input));
    serializer.attribute("encryptedVerifierHashValue", encode_base64(result.key_encryptor.verifier_hash_value));
    serializer.attribute("encryptedKeyValue", encode_base64(result.key_encryptor.encrypted_key_value));
    serializer.end_element(xmlns_p, "encryptedKey");
    serializer.end_element(xmlns, "keyEncryptor");
    serializer.end_element(xmlns, "keyEncryptors");

    serializer.end_element(xmlns, "encryption");

    return encryption_info;
}

std::vector<std::uint8_t> crypto_helper::decrypt_xlsx_agile(
    const std::vector<std::uint8_t> &encryption_info,
    const std::string &password,
    const std::vector<std::uint8_t> &encrypted_package)
{
    static const auto &xmlns = xlnt::constants::ns("encryption");
    static const auto &xmlns_p = xlnt::constants::ns("encryption-password");
    // static const auto &xmlns_c = xlnt::constants::namespace_("encryption-certificate");

    agile_encryption_info result;

    xml::parser parser(encryption_info.data(), encryption_info.size(), "EncryptionInfo");

    parser.next_expect(xml::parser::event_type::start_element, xmlns, "encryption");

    parser.next_expect(xml::parser::event_type::start_element, xmlns, "keyData");
    result.key_data.salt_size = parser.attribute<std::size_t>("saltSize");
    result.key_data.block_size = parser.attribute<std::size_t>("blockSize");
    result.key_data.key_bits = parser.attribute<std::size_t>("keyBits");
    result.key_data.hash_size = parser.attribute<std::size_t>("hashSize");
    result.key_data.cipher_algorithm = parser.attribute("cipherAlgorithm");
    result.key_data.cipher_chaining = parser.attribute("cipherChaining");
    result.key_data.hash_algorithm = parser.attribute("hashAlgorithm");
    result.key_data.salt_value = decode_base64(parser.attribute("saltValue"));
    parser.next_expect(xml::parser::event_type::end_element, xmlns, "keyData");

    parser.next_expect(xml::parser::event_type::start_element, xmlns, "dataIntegrity");
    result.data_integrity.hmac_key = decode_base64(parser.attribute("encryptedHmacKey"));
    result.data_integrity.hmac_value = decode_base64(parser.attribute("encryptedHmacValue"));
    parser.next_expect(xml::parser::event_type::end_element, xmlns, "dataIntegrity");

    parser.next_expect(xml::parser::event_type::start_element, xmlns, "keyEncryptors");
    parser.next_expect(xml::parser::event_type::start_element, xmlns, "keyEncryptor");
    parser.attribute("uri");
    bool any_password_key = false;

    while (parser.peek() != xml::parser::event_type::end_element)
    {
        parser.next_expect(xml::parser::event_type::start_element);

        if (parser.namespace_() == xmlns_p && parser.name() == "encryptedKey")
        {
            any_password_key = true;
            result.key_encryptor.spin_count = parser.attribute<std::size_t>("spinCount");
            result.key_encryptor.salt_size = parser.attribute<std::size_t>("saltSize");
            result.key_encryptor.block_size = parser.attribute<std::size_t>("blockSize");
            result.key_encryptor.key_bits = parser.attribute<std::size_t>("keyBits");
            result.key_encryptor.hash_size = parser.attribute<std::size_t>("hashSize");
            result.key_encryptor.cipher_algorithm = parser.attribute("cipherAlgorithm");
            result.key_encryptor.cipher_chaining = parser.attribute("cipherChaining");

            auto hash_algorithm_string = parser.attribute("hashAlgorithm");
            if (hash_algorithm_string == "SHA512")
            {
                result.key_encryptor.hash = hash_algorithm::sha512;
            }
            else if (hash_algorithm_string == "SHA1")
            {
                result.key_encryptor.hash = hash_algorithm::sha1;
            }
            else if (hash_algorithm_string == "SHA256")
            {
                result.key_encryptor.hash = hash_algorithm::sha256;
            }
            else if (hash_algorithm_string == "SHA384")
            {
                result.key_encryptor.hash = hash_algorithm::sha384;
            }

            result.key_encryptor.salt_value = decode_base64(parser.attribute("saltValue"));
            result.key_encryptor.verifier_hash_input =
                decode_base64(parser.attribute("encryptedVerifierHashInput"));
            result.key_encryptor.verifier_hash_value =
                decode_base64(parser.attribute("encryptedVerifierHashValue"));
            result.key_encryptor.encrypted_key_value = decode_base64(parser.attribute("encryptedKeyValue"));
        }
        else
        {
            throw xlnt::unsupported("other encryption key types not supported");
        }

        parser.next_expect(xml::parser::event_type::end_element);
    }

    if (!any_password_key)
    {
        throw "no password key in keyEncryptors";
    }

    parser.next_expect(xml::parser::event_type::end_element, xmlns, "keyEncryptor");
    parser.next_expect(xml::parser::event_type::end_element, xmlns, "keyEncryptors");

    parser.next_expect(xml::parser::event_type::end_element, xmlns, "encryption");

    // begin key generation algorithm

    // H_0 = H(salt + password)
    auto salt_plus_password = result.key_encryptor.salt_value;
    std::vector<std::uint16_t> password_wide(password.begin(), password.end());

    std::for_each(password_wide.begin(), password_wide.end(), [&salt_plus_password](std::uint16_t c) {
        salt_plus_password.insert(salt_plus_password.end(), reinterpret_cast<char *>(&c),
            reinterpret_cast<char *>(&c) + sizeof(std::uint16_t));
    });

    auto h_0 = hash(result.key_encryptor.hash, salt_plus_password);

    // H_n = H(iterator + H_n-1)
    std::vector<std::uint8_t> iterator_plus_h_n(4, 0);
    iterator_plus_h_n.insert(iterator_plus_h_n.end(), h_0.begin(), h_0.end());
    std::uint32_t &iterator = *reinterpret_cast<std::uint32_t *>(iterator_plus_h_n.data());
    std::vector<std::uint8_t> h_n;

    for (iterator = 0; iterator < result.key_encryptor.spin_count; ++iterator)
    {
        h_n = hash(result.key_encryptor.hash, iterator_plus_h_n);
        std::copy(h_n.begin(), h_n.end(), iterator_plus_h_n.begin() + 4);
    }

    static const std::size_t block_size = 8;

    auto calculate_block = [&result](const std::vector<std::uint8_t> &raw_key,
        const std::array<std::uint8_t, block_size> &block, const std::vector<std::uint8_t> &encrypted) {
        auto combined = raw_key;
        combined.insert(combined.end(), block.begin(), block.end());
        auto key = hash(result.key_encryptor.hash, combined);
        key.resize(result.key_encryptor.key_bits / 8);
        return aes(key, result.key_encryptor.salt_value, encrypted,
            cipher_chaining::cbc, cipher_direction::decryption);
    };

    const std::array<std::uint8_t, block_size> input_block_key = {{0xfe, 0xa7, 0xd2, 0x76, 0x3b, 0x4b, 0x9e, 0x79}};
    auto hash_input = calculate_block(h_n, input_block_key, result.key_encryptor.verifier_hash_input);
    auto calculated_verifier = hash(result.key_encryptor.hash, hash_input);

    const std::array<std::uint8_t, block_size> verifier_block_key = {
        {0xd7, 0xaa, 0x0f, 0x6d, 0x30, 0x61, 0x34, 0x4e}};
    auto expected_verifier = calculate_block(h_n, verifier_block_key, result.key_encryptor.verifier_hash_value);
    expected_verifier.resize(calculated_verifier.size());

    if (calculated_verifier.size() != expected_verifier.size()
        || std::mismatch(calculated_verifier.begin(), calculated_verifier.end(), expected_verifier.begin(),
               expected_verifier.end())
            != std::make_pair(calculated_verifier.end(), expected_verifier.end()))
    {
        throw xlnt::exception("bad password");
    }

    const std::array<std::uint8_t, block_size> key_value_block_key = {
        {0x14, 0x6e, 0x0b, 0xe7, 0xab, 0xac, 0xd0, 0xd6}};
    auto key = calculate_block(h_n, key_value_block_key, result.key_encryptor.encrypted_key_value);

    auto salt_size = result.key_data.salt_size;
    auto salt_with_block_key = result.key_data.salt_value;
    salt_with_block_key.resize(salt_size + sizeof(std::uint32_t), 0);

    auto &segment = *reinterpret_cast<std::uint32_t *>(salt_with_block_key.data() + salt_size);
    auto total_size = static_cast<std::size_t>(*reinterpret_cast<const std::uint64_t *>(encrypted_package.data()));

    std::vector<std::uint8_t> encrypted_segment(segment_length, 0);
    std::vector<std::uint8_t> decrypted_package;
    decrypted_package.reserve(encrypted_package.size() - 8);

    for (std::size_t i = 8; i < encrypted_package.size(); i += segment_length)
    {
        auto iv = hash(result.key_encryptor.hash, salt_with_block_key);
        iv.resize(16);

        auto segment_begin = encrypted_package.begin() + static_cast<std::ptrdiff_t>(i);
        auto current_segment_length = std::min(segment_length, encrypted_package.size() - i);
        auto segment_end = encrypted_package.begin() + static_cast<std::ptrdiff_t>(i + current_segment_length);
        encrypted_segment.assign(segment_begin, segment_end);
        auto decrypted_segment =
            aes(key, iv, encrypted_segment, cipher_chaining::cbc, cipher_direction::decryption);
        decrypted_segment.resize(current_segment_length);

        decrypted_package.insert(decrypted_package.end(), decrypted_segment.begin(), decrypted_segment.end());

        ++segment;
    }

    decrypted_package.resize(total_size);

    return decrypted_package;
}

std::vector<std::uint8_t> crypto_helper::decrypt_xlsx(
    const std::vector<std::uint8_t> &bytes, const std::string &password)
{
    if (bytes.empty())
    {
        throw xlnt::exception("empty file");
    }

    std::vector<char> as_chars(bytes.begin(), bytes.end());
    POLE::Storage storage(as_chars.data(), static_cast<unsigned long>(bytes.size()));

    if (!storage.open())
    {
        throw xlnt::exception("not an ole compound file");
    }

    auto encrypted_package = file(storage, "EncryptedPackage");
    auto encryption_info = file(storage, "EncryptionInfo");

    std::size_t index = 0;

    auto version_major = read_int<std::uint16_t>(index, encryption_info);
    auto version_minor = read_int<std::uint16_t>(index, encryption_info);
    auto encryption_flags = read_int<std::uint32_t>(index, encryption_info);

    // get rid of header
    encryption_info.erase(encryption_info.begin(), encryption_info.begin() + static_cast<std::ptrdiff_t>(index));

    // version 4.4 is agile
    if (version_major == 4 && version_minor == 4)
    {
        if (encryption_flags != 0x40)
        {
            throw xlnt::exception("bad header");
        }

        return decrypt_xlsx_agile(encryption_info, password, encrypted_package);
    }

    // not agile, only try to decrypt versions 3.2 and 4.2
    if (version_minor != 2 || (version_major != 2 && version_major != 3 && version_major != 4))
    {
        throw xlnt::exception("unsupported encryption version");
    }

    if ((encryption_flags & 0b00000011) != 0) // Reserved1 and Reserved2, MUST be 0
    {
        throw xlnt::exception("bad header");
    }

    if ((encryption_flags & 0b00000100) == 0 // fCryptoAPI
        || (encryption_flags & 0b00010000) != 0) // fExternal
    {
        throw xlnt::exception("extensible encryption is not supported");
    }

    if ((encryption_flags & 0b00100000) == 0) // fAES
    {
        throw xlnt::exception("not an OOXML document");
    }

    return decrypt_xlsx_standard(encryption_info, password, encrypted_package);
}

std::vector<std::uint8_t> crypto_helper::encrypt_xlsx(
    const std::vector<std::uint8_t> &bytes, const std::string &password)
{
    if (bytes.empty())
    {
        throw xlnt::exception("empty file");
    }

    generate_agile_encryption_info(password);

    return {};
}

const std::size_t crypto_helper::segment_length = 4096;

void xlsx_consumer::read(std::istream &source, const std::string &password)
{
    std::vector<std::uint8_t> data((std::istreambuf_iterator<char>(source)), (std::istreambuf_iterator<char>()));
    const auto decrypted = crypto_helper::decrypt_xlsx(data, password);
    vector_istreambuf decrypted_buffer(decrypted);
    std::istream decrypted_stream(&decrypted_buffer);
    read(decrypted_stream);
}

void xlsx_producer::write(std::ostream &destination, const std::string &password)
{
    std::vector<std::uint8_t> decrypted;

    {
        vector_ostreambuf decrypted_buffer(decrypted);
        std::ostream decrypted_stream(&decrypted_buffer);
        write(decrypted_stream);
    }

    const auto encrypted = crypto_helper::encrypt_xlsx(decrypted, password);
    vector_istreambuf encrypted_buffer(encrypted);

    destination << &encrypted_buffer;
}

} // namespace detail
} // namespace xlnt