Thread: encrypting and decrypting a string

-Encrypt a string of text using a Caesar Square: the string should be written along the rows of a square that is as small as possible, and then the encrypted string is read down the columns like so:

"A long time ago, in a galaxy far, far away" is first processed to remove case and space, to get alongtimeago,inagalaxyfar,faraway (33 characters long) and is then laid out on a square grid:


a l o n g t
i m e a g o
, i n a g a
l a x y f a
r , f a r a
w a y


The grid is 6 x 6 as 36 is the closest square number that is no less than the number of characters in the message.

Reading form top-to-bottom we get ai,lrwlmia,aoenxfynaayagggfrtoaaa - which is of course garbage
You also have to decrypt such strings which may contain white space that needs to be removed ...


I am struggling to understand how the shifting of elements works. I know decrypting is reading from left to right and encrypting is reading from top to bottom but I can't think of a way to code it. Also I considered that the question has to do with two dimensional arrays but then I didn't know how to determine the amount of rows and columns I needed and hence didn't know what to make each dimension.

So far I have just changed the cypherText(string) into an array called decryptArray, and each element of this array contains a letter within the string. I was up to shifting the elements and I thought of using a FOR loop to do that but there was not much point until I understand how the shifting works. To be honest, I am not even sure if I am on the right track.

public class CaesarBox 
{
 
	public static void main(String[] args) 
	{
 
	    if(args[0].equals("-decrypt"))
	    {
	    	System.out.println(decrypt(args[1]));
	    }
 
	}
 
	public static char decrypt (String cypherText) 
	{
		char example = 'a'+'b'; //ignore this
		int length = cypherText.length(); //determining the length of the string
		char [] decryptArray  = new char [length]; //created an array using the length of what was entered 
		for(int i=0; i < length; i++)
		{
			decryptArray[i]=cypherText.charAt(i); 
                        //making each element of what as typed in to equal an element in the array
			System.out.print(decryptArray[i]);
		}
 
 
		return example; //just put this in as I am not up to this part and so I can compile the program
	}
}

how the shifting of elements works

Can you give an example of "shifting"?

how to determine the amount of rows and columns I needed

Is that the square root of the minimum square number? The Math class has some methods that could help find that.

I don't see how reading the array by rows or reading it by columns is doing any shifting of its contents. The positions of the letters in the array doesn't change.

a is [0][0], b is [0][1], c is [1][0], d is [1][1]

and I wanted to make it so it becomes:

a is [0][0], c is [0][1], b is [1][0], d is [1][1]

I guess by changing the position of the letters and not shifting.. hmm

Why change the array? Why not change how the elements are read from the array?

Is this the same problem: http://www.javaprogrammingforums.com...tml#post107540

The Threads have been merged

Is there some confusion on what the program is supposed to do?
For the encrypt part: What does the program read in, what does it do with what was read and what does it write out?
For the decrypt part, does the program take the output from the encrypt step and convert it to what the encrypt part read in?

What problems are you having?

Work on one method at a time.
In the encrypt method, work on putting the input into the array. When that step works, then move to the next step.

Use this statement for printing out the contents of the array for debugging:

System.out.println("an ID "+ java.util.Arrays.deepToString(theArrayName));

Change "an ID " to describe what is being printed.

I have put the input into a 2-D array

If you have the code to store the String's characters into an array row by row,
now work on the code to take out the characters from the array column by column.
Use a StringBuilder to save the characters and when done, create a String from its contents.