Crearea unui mecanism simplu de codare/decodare

Ganav · June 25, 2014

In urma cu cateva zile am creat un challenge in care se dorea aflarea textului in clar al unui sir de caractere codate:

https://rstforums.com/forum/85978-encode-decode.rst

Pana acum nu am primit niciun raspuns in privinta unei rezolvari sau chiar si a vreunei idei de rezolvare. Drept urmare m-am gandit sa fac publica sursa encoder-ului. A fost scris in Visual C++ Express Edition 2010 care poate fi gasit aici:

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Deschideti Visual Studio si creati un proiect nou de tip consola. La sfarsit inainte de a da click pe Finish asigurati-va ca proiectul nu va folosi antete precompilate(Precompiled headers). Acum creati urmatoarele fisiere antet(Acestea trebuiesc situate in folder-ul "Header Files" vizibil in Project Explorer):

includes.h

#ifndef INCLUDES_H
#define INCLUDES_H

#include <iostream>
#include <string>
#include <algorithm>
#include <utility>
#include <vector>
#include <fstream>


#endif

encoder.h

#ifndef ENCODER_H
#define ENCODER_H

#include "includes.h"

class Char4EncoderDecoder {
private:

	char getEncodedChar(int c);
	int getDecodedChar(char c);
	void reverseStr(std::vector<unsigned char>& input) { std::reverse(input.begin(), input.end()); }
	void bitReverse(std::vector<unsigned char>& input);
	void oddSwap(std::vector<unsigned char>& input);
	void evenSwap(std::vector<unsigned char>& input);

	void formatInput(std::vector<unsigned char>& input);
	void Char4EncoderDecoder::XORConsecutiveBytePairsInv(std::vector<unsigned char>& input);
	void write2dst(std::vector<unsigned char>& dst, std::string& fin_dst);

public:

	void encode(std::string& src, std::string& dst);
	void decode(std::string& src, std::string& dst);

};

#endif

Acum ne trebuiesc fisierele sursa(unde sunt implementate metodele claselor din fisierele antet). Adaugam in folderul "Source Files" din Project Explorer urmatoarele fisiere:

encoder.cpp

#include "includes.h"
#include "encoder.h"

void Char4EncoderDecoder::bitReverse(std::vector<unsigned char>& input) {
	for(size_t i = 0; i < input.size(); i++)
		input[i] = (input[i] * 0x0202020202ULL & 0x010884422010ULL) % 1023;
}

void Char4EncoderDecoder::oddSwap(std::vector<unsigned char>& input) {
	for(size_t i = 0; i < input.size() / 2; i++)
		if(input[i] % 2) {
			input[i] ^= input[input.size()/2+i];
			input[input.size()/2+i] ^= input[i];
			input[i] ^= input[input.size()/2+i];
		}
}

void Char4EncoderDecoder::evenSwap(std::vector<unsigned char>& input) {
	for(size_t i = 0; i < input.size() / 2; i++)
		if(input[i] % 2 == 0) {
			input[input.size()/2+i] ^= input[i];
			input[i] ^= input[input.size()/2+i];
			input[input.size()/2+i] ^= input[i];
		}
}

void Char4EncoderDecoder::encode(std::string& src, std::string& dst) {
	std::vector<unsigned char> byte_dst(src.begin(), src.end());
	dst.clear();

	// Reverse the source string
	this->reverseStr(byte_dst);	
	// Bit reverse the source string
	this->bitReverse(byte_dst);
	// Swap even 
	this->evenSwap(byte_dst);
	// Odd swap
	this->oddSwap(byte_dst);
	write2dst(byte_dst, dst);
}

void Char4EncoderDecoder::decode(std::string& src, std::string& dst) {
	std::vector<unsigned char> byte_dst(src.begin(), src.end());
	dst.clear();
	// Format input into bytes
	formatInput(byte_dst);
	// Odd swap
	this->oddSwap(byte_dst);
	// Swap even 
	this->evenSwap(byte_dst);
	// Bit reverse the source string
	this->bitReverse(byte_dst);
	// Reverse the source string
	this->reverseStr(byte_dst);

	dst.resize(byte_dst.size());
	for(size_t i = 0; i < byte_dst.size(); i++)
		dst[i] = byte_dst[i];
}

void Char4EncoderDecoder::formatInput(std::vector<unsigned char>& input) {
	// Format input 
	if(input.size() % 4 != 0) {
		size_t aux = input.size() % 4;
		for(size_t i = 0; i < aux; i++) 
			input.push_back('[');
	}
	// Extract bits and create results vector
	std::vector<unsigned char> dst;
	dst.resize(input.size() / 4);
	for(size_t i = 0; i < input.size(); i += 4) {
		dst[i/4] |= getDecodedChar(input[i]);
		dst[i/4] |= getDecodedChar(input[i+1]) << 2;
		dst[i/4] |= getDecodedChar(input[i+2]) << 4;
		dst[i/4] |= getDecodedChar(input[i+3]) << 6;
	}
	input = dst;
}

int Char4EncoderDecoder::getDecodedChar(char c) {
	if(c == '[') 
		return 0;
	else if(c == '<')
		return 1;
	else if(c == '>')
		return 2;
	else if(c == ']')
		return 3;
	else
		return -1;
}

char Char4EncoderDecoder::getEncodedChar(int c) { 
	if(c == 0) 
		return '[';
	else if(c == 1) 
		return '<';
	else if(c == 2)
		return '>';
	else if(c == 3)
		return ']';
	else 
		return -1;
}

void Char4EncoderDecoder::write2dst(std::vector<unsigned char>& dst, std::string& fin_dst) {
	std::vector<unsigned char> tmp_dst;
	for(size_t i = 0; i < dst.size(); i++) {
			tmp_dst.push_back(getEncodedChar((int)dst[i] & 0x03));
			tmp_dst.push_back(getEncodedChar((int)(dst[i] & 0x0c) >> 2));
			tmp_dst.push_back(getEncodedChar((int)(dst[i] & 0x30) >> 4));
			tmp_dst.push_back(getEncodedChar((int)(dst[i] & 0xC0) >> 6));
	}
	fin_dst.clear(); fin_dst.resize(tmp_dst.size());
	for(size_t i = 0; i < tmp_dst.size(); i++)
		fin_dst[i] = tmp_dst[i];
	// std::cin.get();
}

main.cpp

#include "includes.h"
#include "encoder.h"

void challengeRST(void) {
	Char4EncoderDecoder *enc = 0;
	std::string src, dst;
	std::ofstream f;

	f.open ("RST_out.txt");
	enc = new Char4EncoderDecoder();

	src = "RST Forums";
	enc->encode(src, dst); 
	std::cout << "Encoded value: " << dst << "\n";
	enc->decode(dst, src);
	std::cout << "Decoded value: " << src << "\n";

	src = "abc";
	enc->encode(src, dst); 
	std::cout << "Encoded value: " << dst << "\n";
	f << "Encoded value: " << dst << "\n";
	enc->decode(dst, src);
	std::cout << "Decoded value: " << src << "\n";
	f << "Encoded value: " << src << "\n";

	src = "abc123";
	enc->encode(src, dst); 
	std::cout << "Encoded value: " << dst << "\n";
	f << "Encoded value: " << dst << "\n";
	enc->decode(dst, src);
	std::cout << "Decoded value: " << src << "\n";
	f << "Encoded value: " << src << "\n";

	src = "The quick brown fox jumps over the lazy dog";
	enc->encode(src, dst); 
	std::cout << "Encoded value: " << dst << "\n";
	f << "Encoded value: " << dst << "\n";
	enc->decode(dst, src);
	std::cout << "Decoded value: " << src << "\n";
	f << "Encoded value: " << src << "\n";

	src = "Romanian Security Team 2006 - 2014";
	enc->encode(src, dst); 
	std::cout << "Encoded value: " << dst << "\n";
	f << "Encoded value: " << dst << "\n";
	enc->decode(dst, src);
	std::cout << "Decoded value: " << src << "\n";
	f << "Encoded value: " << src << "\n";

	std::cout << "Done\n";
	std::cin.get();
	delete enc;
	enc = 0;
	f.close();
}

void usage(char *argv) {
	std::cout << "Usage: " << argv << "<-e/-d> <to be encoded string> \n";
	std::exit(0);
}

int main(int argc, char **argv) {
#ifndef NDEBUG
	challengeRST();
#else
	if(argc != 3) 
		usage(argv[0]);

	Char4EncoderDecoder *enc = 0;
	enc = new Char4EncoderDecoder();

	std::string ed("argv[1]");
	std::string src("argv[2]");
	std::string dst;

	if(ed == "-e") {
		enc->encode(src, dst);
		std::cout << "Encoded string: " << dst << "\n";
	} else if(ed == "-d") {
		enc->decode(src, dst);
		std::cout << "Decoded string: " << dst << "\n";
	} else {
		usage(argv[0]);
	}
        // Deallocate memory
        delete enc;
        enc = 0;
#endif

	return 0;
}

Algoritmul poate fi dezvoltat in continuare adaugand mai multe etape de procesare.

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