Simple Encryption

[sec_ware]

Hi


A question difficult to answer. A while ago, I wrote a post[1]
which tries to answer that. In my opinion, cryptography
(the encoding of messages) is simpler than cryptanalysis, in terms
of mathematical skills needed. And also simpler, in terms of
persistency needed...


For convenience, a few definitions:


Def: cryptography
the study of means of converting information from its normal, comprehensible form
into an incomprehensible format, rendering it unreadable without secret knowledge —
the art of encryption[2]

Def: cryptanalysis
The study of how to circumvent the use of cryptography is called cryptanalysis[3]

Def: cryptology
cryptography and cryptanalysis are grouped together under the umbrella term cryptology

Cheers.

[1] http://www.antionline.com/showthread...hreadid=264224
[2] http://en.wikipedia.org/wiki/Cryptography
[3] http://en.wikipedia.org/wiki/Cryptanalysis

[Death_Knight]

/*
 * Created on Mar 2, 2005
 */
import java.io.*;


public class Encryption
{
    public void encrypt(String str, String key)
    {
        char[] message = str.toCharArray();
        int len = message.length;
        char[] encrypt = new char[len];

        int key_ = Integer.parseInt(key);

        if (key_ < 0)
        {
            key_ = (key_ * -1);
        }

        for (int x = 0; x < len; ++x)
        {
            encrypt[x] = message[(x + key_) % len];
        }

        for (int y = 0; y < len; ++y)
        {
            encrypt[y] = (char) (((int) encrypt[y] + key_) % 128);
        }

        write(new String(encrypt));

        get_input();
    }

    public void decrypt(String key)
    {
        char[] decrypt = read().toCharArray();
        int len = decrypt.length;
        char[] message = new char[len];

        int key_ = Integer.parseInt(key);

        if (key_ < 0)
        {
            key_ = (key_ * -1);
        }

        int shift = 0;

        for (int x = 0; x < len; ++x)
        {
            shift = ((int) decrypt[x] - key_) % 128;

            if (shift < 0)
            {
                shift += 128;
            }

            decrypt[x] = (char) (shift);
        }

        int mov = 0;

        for (int y = 0; y < len; ++y)
        {
            mov = (y - key_) % len;

            if (mov < 0)
            {
                mov += len;
            }

            message[y] = decrypt[mov];
        }

        System.out.println("Message: " + new String(message));

        get_input();
    }

    public void get_input()
    {
        System.out.println("1. Encrypt.");
        System.out.println("2. Decrypt.");
        System.out.println("3. Exit.");
        System.out.print("Your choice: ");

        try
        {
            BufferedReader in = new BufferedReader(new InputStreamReader(
                        System.in));
            String str = "";

            str = in.readLine();

            int option = Integer.parseInt(str);

            switch (option)
            {
                case 1:
                    System.out.print("Enter message: ");

                    String message = in.readLine();

                    System.out.print("Enter key to encrypt: ");

                    String key = in.readLine();

                    encrypt(message, key);

                    break;

                case 2:
                    System.out.print("Enter key to decrypt: ");

                    String key_ = in.readLine();
                    decrypt(key_);

                    break;

                case 3:
                    System.exit(0);

                    break;

                default:
                    System.out.println("Invalid option.");
                    get_input();
            }
        }
        catch (IOException e)
        {
        }
    }

    public String read()
    {
        String str = "";

        try
        {
            BufferedReader in = new BufferedReader(new FileReader("message.txt"));
            str = in.readLine();
            in.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }

        return str;
    }

    public void write(String str)
    {
        try
        {
            BufferedWriter out = new BufferedWriter(new FileWriter(
                        "message.txt"));
            out.write(str);
            out.close();

            System.out.println("message.txt created.");
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }

    public static void main(String[] agrs)
    {
        Encryption en = new Encryption();
        en.get_input();
    }
}

My first attemp on cryptograhy program. pardon me for the bad programming.