/*

 * This file is part of OpenTTD.

 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.

 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.

 */

/** @file signature.cpp Implementation of signature validation routines. */

#include "stdafx.h"

#include "signature.h"

#include "debug.h"

#include "fileio_func.h"

#include "string_func.h"

#include "3rdparty/monocypher/monocypher.h"

#include "3rdparty/monocypher/monocypher-ed25519.h"

#include "3rdparty/nlohmann/json.hpp"

#include "safeguards.h"

/** The public keys used for signature validation. */

static const std::initializer_list<std::array<uint8_t, 32>> _public_keys_v1 = {

	/* 2024-01-20 - Public key for Social Integration Plugins. */

	{ 0xed, 0x5d, 0x57, 0x47, 0x21, 0x99, 0x8b, 0x02, 0xdf, 0x6e, 0x3d, 0x69, 0xe1, 0x87, 0xca, 0xd0, 0x0e, 0x88, 0xc3, 0xe2, 0xb2, 0xa6, 0x7b, 0xc0, 0x42, 0xc8, 0xd6, 0x4b, 0x65, 0xe6, 0x48, 0xf7 },

};

/**

 * Calculate the 32-byte blake2b hash of a file.

 *

 * @param filename The filename to calculate the hash of.

 * @return The 32-byte blake2b hash of the file, hex-encoded.

 */

static std::string CalculateHashV1(const std::string &filename)

{

	FILE *f = FioFOpenFile(filename, "rb", NO_DIRECTORY);

	if (f == nullptr) {

		return "";

	}

	std::array<uint8_t, 32> digest;

	crypto_blake2b_ctx ctx;

	crypto_blake2b_init(&ctx, digest.size());

	while (!feof(f)) {

		std::array<uint8_t, 1024> buf;

		size_t len = fread(buf.data(), 1, buf.size(), f);

		crypto_blake2b_update(&ctx, buf.data(), len);

	}

	fclose(f);

	crypto_blake2b_final(&ctx, digest.data());

	return FormatArrayAsHex(digest);

}

/**

 * Validate whether the checksum of a file is the same.

 *

 * @param filename The filename to validate the checksum of.

 * @param checksum The expected checksum.

 * @return True iff the checksum of the file is the same as the expected checksum.

 */

static bool ValidateChecksum(const std::string &filename, const std::string &checksum)

{

	/* Checksums are "<version>$<hash>". Split out the version. */

	auto pos = checksum.find('$');

	assert(pos != std::string::npos); // Already validated by ValidateSchema().

	const std::string version = checksum.substr(0, pos);

	const std::string hash = checksum.substr(pos + 1);

	/* Calculate the checksum over the file. */

	std::string calculated_hash;

	if (version == "1") {

		calculated_hash = CalculateHashV1(filename);

	} else {

		Debug(misc, 0, "Failed to validate signature: unknown checksum version: {}", filename);

		return false;

	}

	/* Validate the checksum is the same. */

	if (calculated_hash.empty()) {

		Debug(misc, 0, "Failed to validate signature: couldn't calculate checksum for: {}", filename);

		return false;

	}

	if (calculated_hash != hash) {

		Debug(misc, 0, "Failed to validate signature: checksum mismatch for: {}", filename);

		return false;

	}

	return true;

}

/**

 * Validate whether the signature is valid for this set of files.

 *

 * @param signature The signature to validate.

 * @param files The files to validate the signature against.

 * @param filename The filename of the signatures file (for error-reporting).

 * @return True iff the signature is valid for this set of files.

 */

static bool ValidateSignature(const std::string &signature, const nlohmann::json &files, const std::string &filename)

{

	/* Signatures are "<version>$<signature>". Split out the version. */

	auto pos = signature.find('$');

	assert(pos != std::string::npos); // Already validated by ValidateSchema().

	const std::string version = signature.substr(0, pos);

	const std::string sig_value = signature.substr(pos + 1);

	/* Create the message we are going to validate. */

	std::string message = files.dump(-1);

	/* Validate the signature. */

	if (version == "1") {

		std::array<uint8_t, 64> sig;

		if (sig_value.size() != 128 || !ConvertHexToBytes(sig_value, sig)) {

			Debug(misc, 0, "Failed to validate signature: invalid signature: {}", filename);

			return false;

		}

		for (auto &pk_value : _public_keys_v1) {

			/* Check if the message is valid with this public key. */

			auto res = crypto_ed25519_check(sig.data(), pk_value.data(), reinterpret_cast<uint8_t *>(message.data()), message.size());

			if (res == 0) {

				return true;

			}

		}

		Debug(misc, 0, "Failed to validate signature: signature validation failed: {}", filename);

		return false;

	} else {

		Debug(misc, 0, "Failed to validate signature: unknown signature version: {}", filename);

		return false;

	}

	return true;

}

/**

 * Validate the signatures file complies with the JSON schema.

 *

 * @param signatures The signatures JSON to validate.

 * @param filename The filename of the signatures file (for error-reporting).

 * @return True iff the signatures file complies with the JSON schema.

 */

static bool ValidateSchema(const nlohmann::json &signatures, const std::string &filename)

{

	if (signatures["files"].is_null()) {

		Debug(misc, 0, "Failed to validate signature: no files found: {}", filename);

		return false;

	}

	if (signatures["signature"].is_null()) {

		Debug(misc, 0, "Failed to validate signature: no signature found: {}", filename);

		return false;

	}

	for (auto &signature : signatures["files"]) {

		if (signature["filename"].is_null() || signature["checksum"].is_null()) {

			Debug(misc, 0, "Failed to validate signature: invalid entry in files: {}", filename);

			return false;

		}

		const std::string sig_filename = signature["filename"];

		const std::string sig_checksum = signature["checksum"];

		if (sig_filename.empty() || sig_checksum.empty()) {

			Debug(misc, 0, "Failed to validate signature: invalid entry in files: {}", filename);

			return false;

		}

		auto pos = sig_checksum.find('$');

		if (pos == std::string::npos) {

			Debug(misc, 0, "Failed to validate signature: invalid checksum format: {}", filename);

			return false;

		}

	}

	const std::string signature = signatures["signature"];

	auto pos = signature.find('$');

	if (pos == std::string::npos) {

		Debug(misc, 0, "Failed to validate signature: invalid signature format: {}", filename);

		return false;

	}

	return true;

}

/**

 * Validate that the signatures mentioned in the signature file are matching

 * the files in question.

 *

 * @return True iff the files in the signature file passed validation.

 */

static bool _ValidateSignatureFile(const std::string &filename)

{

	size_t filesize;

	FILE *f = FioFOpenFile(filename, "rb", NO_DIRECTORY, &filesize);

	if (f == nullptr) {

		Debug(misc, 0, "Failed to validate signature: file not found: {}", filename);

		return false;

	}

	std::string text(filesize, '\0');

	size_t len = fread(text.data(), filesize, 1, f);

	if (len != 1) {

		Debug(misc, 0, "Failed to validate signature: failed to read file: {}", filename);

		return false;

	}

	nlohmann::json signatures;

	try {

		signatures = nlohmann::json::parse(text);

	} catch (nlohmann::json::exception &) {

		Debug(misc, 0, "Failed to validate signature: not a valid JSON file: {}", filename);

		return false;

	}

	/*

	 * The JSON file should look like:

	 *

	 *   {

	 *     "files": [

	 *       {

	 *         "checksum": "version$hash"

	 *         "filename": "filename",

	 *       },

	 *       ...

	 *     ],

	 *     "signature": "version$signature"

	 *   }

	 *

	 * The signature is a signed message of the content of "files", dumped as

	 * JSON without spaces / newlines, keys in the order as indicated above.

	 */

	if (!ValidateSchema(signatures, filename)) {

		return false;

	}

	if (!ValidateSignature(signatures["signature"], signatures["files"], filename)) {

		return false;

	}

	std::string dirname = std::filesystem::path(filename).parent_path().string();

	for (auto &signature : signatures["files"]) {

		const std::string sig_filename = dirname + PATHSEPCHAR + signature["filename"].get<std::string>();

		const std::string sig_checksum = signature["checksum"];

		if (!ValidateChecksum(sig_filename, sig_checksum)) {

			return false;

		}

	}

	return true;

}

/**

 * Validate that the signatures mentioned in the signature file are matching

 * the files in question.

 *

 * @note if ALLOW_INVALID_SIGNATURE is defined, this function will always

 * return true (but will still report any errors in the console).

 *

 * @return True iff the files in the signature file passed validation.

 */

bool ValidateSignatureFile(const std::string &filename)

{

	auto res = _ValidateSignatureFile(filename);;

#if defined(ALLOW_INVALID_SIGNATURE)

	(void)res; // Ignore the result.

	return true;

#else

	return res;

#endif

}