xlnt/source/detail/xlsx_crypto.cpp

// Copyright (c) 2014-2016 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 <array>
#include <pole.h>
#include <botan_all.h>
#include <include_libstudxml.hpp>

#include <detail/vector_streambuf.hpp>
#include <detail/xlsx_consumer.hpp>
#include <xlnt/utils/exceptions.hpp>
#include <xlnt/workbook/workbook.hpp>

namespace xlnt {
namespace detail {

static const std::size_t segment_length = 4096;

enum class cipher_algorithm
{
	aes,
	rc2,
	rc4,
	des,
	desx,
	triple_des,
	triple_des_112
};

enum class cipher_chaining
{
	ecb, // electronic code book
	cbc, // cipher block chaining
	cfb // cipher feedback chaining
};

enum class cipher_direction
{
    encryption,
    decryption
};

enum class hash_algorithm
{
	sha1,
	sha256,
	sha384,
	sha512,
	md5,
	md4,
	md2,
	ripemd128,
	ripemd160,
	whirlpool
};

std::vector<std::uint8_t> aes(const std::vector<std::uint8_t> &key,
    const std::vector<std::uint8_t> &iv,
	const std::vector<std::uint8_t> &encrypted,
    cipher_chaining chaining, cipher_direction direction)
{
    std::string cipher_name("AES-");
    cipher_name.append(std::to_string(key.size() * 8));
    cipher_name.append(chaining == cipher_chaining::ecb
        ? "/ECB/NoPadding" : "/CBC/NoPadding");

    auto botan_direction = direction == cipher_direction::decryption
        ? Botan::DECRYPTION : Botan::ENCRYPTION;
    Botan::Pipe pipe(Botan::get_cipher(cipher_name, key, iv, botan_direction));
    pipe.process_msg(encrypted);
    auto decrypted = pipe.read_all();

    return std::vector<std::uint8_t>(decrypted.begin(), decrypted.end());
}

std::vector<std::uint8_t> decode_base64(const std::string &encoded)
{
    Botan::Pipe pipe(new Botan::Base64_Decoder);
    pipe.process_msg(encoded);
    auto decoded = pipe.read_all();

	return std::vector<std::uint8_t>(decoded.begin(), decoded.end());
};

std::vector<std::uint8_t> hash(hash_algorithm algorithm,
    const std::vector<std::uint8_t> &input)
{
    Botan::Pipe pipe(new Botan::Hash_Filter(
        algorithm == hash_algorithm::sha512 ? "SHA-512" : "SHA-1"));
    pipe.process_msg(input);
    auto hash = pipe.read_all();

	return std::vector<std::uint8_t>(hash.begin(), hash.end());
};

std::vector<std::uint8_t> get_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;
}

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;
};

struct standard_encryption_info
{
	const std::size_t spin_count = 50000;
	std::size_t block_size;
	std::size_t key_bits;
	std::size_t key_bytes;
	std::size_t hash_size;
	cipher_algorithm cipher;
	cipher_chaining chaining;
	const hash_algorithm hash = hash_algorithm::sha1;
	std::vector<std::uint8_t> salt_value;
	std::vector<std::uint8_t> verifier_hash_input;
	std::vector<std::uint8_t> verifier_hash_value;
	std::vector<std::uint8_t> encrypted_key_value;
};

std::vector<std::uint8_t> 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() + offset)),
		reinterpret_cast<const std::uint16_t *>(&*(encryption_info.begin() + 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() + offset,
		encryption_info.begin() + 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() + offset,
		encryption_info.begin() + 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() + offset, 
		encryption_info.begin() + offset + 32);
	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() + info.key_bytes);

	//todo: verify here

	std::size_t package_offset = 0;
	auto decrypted_size = 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;
}


struct agile_encryption_info
{
	// key data
	struct
	{
		std::size_t salt_size;
		std::size_t block_size;
		std::size_t key_bits;
		std::size_t hash_size;
		std::string cipher_algorithm;
		std::string cipher_chaining;
		std::string hash_algorithm;
		std::vector<std::uint8_t> salt_value;
	} key_data;

	struct
	{
		std::vector<std::uint8_t> hmac_key;
		std::vector<std::uint8_t> hmac_value;
	} data_integrity;

	struct
	{
		std::size_t spin_count;
		std::size_t salt_size;
		std::size_t block_size;
		std::size_t key_bits;
		std::size_t hash_size;
		std::string cipher_algorithm;
		std::string cipher_chaining;
	        hash_algorithm hash;
		std::vector<std::uint8_t> salt_value;
		std::vector<std::uint8_t> verifier_hash_input;
		std::vector<std::uint8_t> verifier_hash_value;
		std::vector<std::uint8_t> encrypted_key_value;
	} key_encryptor;
};

std::vector<std::uint8_t> 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 = std::string("http://schemas.microsoft.com/office/2006/encryption");
	static const auto xmlns_p = std::string("http://schemas.microsoft.com/office/2006/keyEncryptor/password");
	static const auto xmlns_c = std::string("http://schemas.microsoft.com/office/2006/keyEncryptor/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);

	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 decrypted_segment = aes(key, iv, std::vector<std::uint8_t>(
			encrypted_package.begin() + i, encrypted_package.begin() + i + segment_length),
            cipher_chaining::cbc, cipher_direction::decryption);
		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> 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 = get_file(storage, "EncryptedPackage");
	auto encryption_info = get_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() + 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);
}

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 = decrypt_xlsx(data, password);
	vector_istreambuf decrypted_buffer(decrypted);
	std::istream decrypted_stream(&decrypted_buffer);
	read(decrypted_stream);
}

} // namespace detail
} // namespace xlnt