Help with a simple encryption program??

[yottabyte]

Hey bytes, you may or may not remember but last time I was here a few months ago I got some help with making a hangman program which went well. Now I'm still doing okay in Java this year but I'm starting a new project for simple encryption and decryption.

The way I set up the program to work is just to add 1 to each character to change a message... (example: "hello" becomes "ifmmp") or subtract 1 from each character to decrypt a message the user enters.

But doing the encryption that way has problems too. I want to have a range of numbres from 0-9, letters from a-z, and A-Z. The problem is if I have the letter z, it doesn't go back to a...which is logically correct since the next character in the unicode is {

Same with spaces. I want spaces to go ignored in the encrypted version of the message instead of becoming "!"...

Here is the code

    public static void encrypt()
    {
    	System.out.println("Enter a message that you would like to encrypt\n");
    	
    	String s1=In.getString();
    	char [] array = s1.toCharArray();
    	
    	for(int index=0; index<array.length; index++)                                
    	{
    		array[index]++;
    	}
    	
    	String encrypted = new String(array);
    	
    	System.out.println("\nYour message has been encrypted to...\n");
    	
    	System.out.println(encrypted);

    	In.getChar();
    	clear();
    }
    
    public static void decrypt()
    {
    	System.out.println("Please enter a message you would like to decrypt\n");
    	
    	String s2=In.getString();
    	char [] array2 = s2.toCharArray();
    	
    	for (int index=0; index<array2.length; index++)
    	{
    		array2[index]--;
    	}
    	
    	String decrypted = new String(array2);
    	
    	System.out.println("\nYour message has been decrypted to...\n");
    	
    	System.out.println(decrypted);
    	
    	In.getChar();
    	clear();

I asked my teacher for a bit of help but I don't understand what his clues meant. He said something about the number 26 being important to this whole thing...can anyone help me make my program to encrypt letters to letters???

[JosAH]

Here's a hint: think of this String:

String enc= "bcdefghijklmnopqrstuvwxyza";

If a character, say, x is an element of this String, the next value is >= 0

int index= enc.indexOf(x);

And the encrypted character y is:

char y= enc.charAt(x-'a');

Decrypting a character y is:

char x= (char)('a'+enc.indexOf(y));

note that the enc String could've been "1234567890 " or " ".

kind regards,

Jos

[yottabyte]

Ok I figured out a way to fix the problem with spaces and letters and the like. (I don't have the updated code on this computer but it's there I assure you :P)

I want to make an option that allows users to encrypt by a certain number that they choose, how do i do that?

As you can see I can probably place a message that asks by how much do you want to encrypt? If they write 2 for example, it adds two instead of one. I just don't know where to put that...and i need a reply for this soon since my deadline is coming up can anyone help please??

System.out.println("Enter a message that you would like to encrypt\n");
    	
    	String s1=In.getString();
    	char [] array = s1.toCharArray();
    	
    	for(int index=0; index<array.length; index++)                                
    	{
    		array[index]++;
    	}
    	
    	String encrypted = new String(array);
    	
    	System.out.println("\nYour message has been encrypted to...\n");
    	
    	System.out.println(encrypted);

[yottabyte]

Never mind I fixed it