Kriptozaštita

Kriptozaštita tekstualnih poruka je izuzetno interesantna oblast sa aspekta programiranja.U pitanju je šifrovanje podataka s ciljem da tačnu informaciju može da vidi samo odabrana osoba. Postoje različiti Algoritmi i rešenja za kriptozaštitu , a dole navedeno je jedno od jednostavnijih. U pitanju je "rotacija" , uvećanje vrednosti ASCII koda za slova u okviru tekstualne poruke za određenu vrednost koja se odredi unosom putem tastature. Sobzirom da je svako slovo na kompjuteru predstavljeno jedinstvenim brojem ASCII kodom ( a = 65 , b = 66 , c = 67 itd) uvećanjem te vrednosti za svako slovo u poruci za određenu vrednost recimo jedan ( a = 65 + 1 postaje slovo b , b = 66 +1 postaje slovo c itd) dobijamo potpuno novu poruku koja je nerazumljiva svima osim onome ko ima ključ za dešifrovanje. Osoba koja treba da pročita poruku mora da ima tekstšifrovane poruke i vrednost ključa za koju se vrši umanjenje vrednosti ASCII koda.Pažnja program samo šifuje podatke , program za dešifrovanje probajte da napravite sami. Potrebno je da se promeni samo jedan karakter u programu Encryption pa da postane Decryption :)) Ukoliko ne ide na dole navedenom linku imate dva programa Encryption i Decryption. Pokušajte da uz pomoć Encryption programa šifrujete poruku, a zatim da je dešifrujete uz pomoć Decryption programa,kao što je prikazano na slici.

Na kraju strane se nalazi link za preuzimanje kompletnog projekta za IDE SharpDevelop C# 4.0. Ukoliko koristite ovo integrisano okruženje, kada preuzmete projekat i otvorite ga možete pogledati kompletan program i menjati ga po želji. Proučite dole prikazan programski kod i sve će vam biti jasno.

/*

* Created by Perić Željko

* periczeljkosmederevo@yahoo.com

* IDE Sharp Develop C#

* Date: 28.11.2011

* Time: 11:20

*

* This is a simple console application for encryption of short

* text messages (up to 255 caracters).It is based on

* increasing of generic ASCII code of letters in text messages

* by value of Rotation_key enterd trough keyboard.

*

* example : Rotation_key = 1

* Message = ABC (ASCII : 65 , 66 , 67)

* Encrypted = BCD (ASCII : 66 ,67 , 68)

*

* Since the value of the ASCII code is limited ,

* so the value of the Rotation_key should be limited

* it is up to you to find min and max values.

* When you do that , given key name will be justified.

*

* !!! The program is not final because it has no part to check

* what exactly user had entered on the keyboard

* there should be try...parse...catch part.

* it is up to you.

* It allso can be modifed to load .txt document,

* encrypt text from it and then send it trough mail,

* for example.

* There is only part of program for encryption,

* the other part for decryption you shuld write

* yourself.Look at this code it should be easy.

* !!!

*

* Good luck and happy learning of C#

*

*/

using System;

namespace Encryption

{

class Program

{

public static void Main(string[] args)

{

//

// variables declaration

//

string Original_Message = "";

string Encrypted_Message = "";

string Original_Message_Letter_String = "";

string Encrypted_Message_Letter_String = "";

string Rotation_key_string = "";

char Original_Message_Letter_Char = ' ';

char Encrypted_Message_Letter_Char = ' ';

int Letter_code = 0;

int Rotation_key_number = 0;

int Message_Lenght = 0;

int Counter = 0;

//

// Hello to user

//

Console.Title = "Encryption program";

Console.SetWindowSize(80,25);

Console.Clear();

Console.ForegroundColor = ConsoleColor.Green;

Console.WriteLine("-------------------------------------------------");

Console.WriteLine(" Program for encryption of text messages");

Console.WriteLine("-------------------------------------------------");

Console.WriteLine("");

//

// Get text message from console

//

Console.WriteLine("Type your message here :");

Console.WriteLine("------------------------");

Original_Message = Console.ReadLine();

Console.WriteLine("");

//

// Get value of rotation key from console

// and transfer it to number

//

Console.WriteLine("Value of rotation key :");

Console.WriteLine("------------------------");

Rotation_key_string = Console.ReadLine();

Rotation_key_number = int.Parse(Rotation_key_string);

Console.WriteLine("------------------------");

Console.WriteLine("");

//

// Encrypt message

//

Message_Lenght = Original_Message.Length;

Counter = 0;

while(Counter < Message_Lenght)

{

Original_Message_Letter_String = Original_Message.Substring(Counter,1);

Original_Message_Letter_Char = char.Parse(Original_Message_Letter_String);

Letter_code = Original_Message_Letter_Char;

Letter_code = Letter_code + Rotation_key_number;

Encrypted_Message_Letter_Char = (char) Letter_code;

Encrypted_Message_Letter_String = Encrypted_Message_Letter_Char.ToString();

Encrypted_Message = Encrypted_Message + Encrypted_Message_Letter_String;

Counter = Counter + 1;

}

//

// Write encrypted message on console

//

Console.WriteLine("Encrypted message");

Console.WriteLine("-------------------------------------------------");

Console.WriteLine(Encrypted_Message);

Console.WriteLine("-------------------------------------------------");

Console.WriteLine("");

//

// End of program

//

Console.Write("Press any key to continue . . . ");

Console.ReadKey(true);

}