encryption_functions.cpp

//////////////////////////////////////////////////
//
//  This work is licensed under the MIT license.
//  
//  You are free to copy, modify and distribute
//  this work freely given that proper attribution
//  is supplied and the author is not held liable.
//  See LICENSE for details.
//  
//  Copyright (c) 2016-2018 David "OmniTroid" Skoland
//
//////////////////////////////////////////////////

#include "encryption_functions.h"

#include "hex_functions.h"

#include <cstddef>
#include <stdlib.h>
#include <sstream>
#include <iomanip>
#include <QVector>

QString fanta_encrypt(QString temp_input, unsigned int p_key)
{
	//using standard stdlib types is actually easier here because of implicit char<->int conversion
	//which in turn makes encryption arithmetic easier

	unsigned int key = p_key;
	unsigned int C1 = 53761;
	unsigned int C2 = 32618;

	QVector<uint_fast8_t> temp_result;
	std::string input = temp_input.toUtf8().constData();

	for (unsigned int pos = 0 ; pos < input.size() ; ++pos)
	{
		uint_fast8_t output = input.at(pos) ^ (key >> 8) % 256;
		temp_result.append(output);
		key = (temp_result.at(pos) + key) * C1 + C2;
	}

	std::string result = "";

	for (uint_fast8_t i_int : temp_result)
	{
		result += omni::int_to_hex(i_int);
	}

	QString final_result = QString::fromStdString(result);

	return final_result;
}

QString fanta_decrypt(QString temp_input, unsigned int key)
{
	std::string input = temp_input.toUtf8().constData();

	QVector<unsigned int> unhexed_vector;

	for(unsigned int i=0; i< input.length(); i+=2)
	{
		std::string byte = input.substr(i,2);
		unsigned int hex_int = strtoul(byte.c_str(), nullptr, 16);
		unhexed_vector.append(hex_int);
	}

	unsigned int C1 = 53761;
	unsigned int C2 = 32618;

	std::string result = "";

	for (int pos = 0 ; pos < unhexed_vector.size() ; ++pos)
	{
		unsigned char output = unhexed_vector.at(pos) ^ (key >> 8) % 256;
		result += output;
		key = (unhexed_vector.at(pos) + key) * C1 + C2;
	}

	return QString::fromStdString(result);

}