Code used trying to work out a cipher for Cyber Security Challenge

gistfile1.java

package m0rjc.test;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;

/**
 * Decode the hex string from a Cyber Security Challenge question.
 * This code is enough to get the job done, rather than something neat.
 *
 * @author Richard Corfield <[email protected]>
 */
public class Decoding
{
	/**
	 * Base64 decode result from http://www.base64decode.org/
	 */
	private static final String HEX = "53 23 e2 13 d2 77 a6 14 03 23 52 64 84 94 83 53 b4 84 73 03 23 52 a6 36 a6 e2 17 17 66 26 a6 77 e6 b6 d2 37 e6 26 84 53 52 66 97 66 94 03 23 52 37 47 e6 97 66 86 e6 17 57 57 64 84 53 52 15 37 47 97 17 e6 27 66 d4 84 53 52 64 33 52 84 03 23 52 a4 a5 15 74 d2 25 75 a4 95 d2 95 35 e4";

	public static void main(final String[] args) throws UnsupportedEncodingException
	{
		// Initially I'd swapped nibbles, decoded then noted it had to be reversed.
		// This way is shorter.
		String input = swapNibblesAndDecodeHex();
		System.out.println("Reverse, -> ASCII: " + input);

		// First pass tried all values for n to see if any looked interesting,
		// though given I needed to make %5H valid it needed to be a small back step.
		String rot21 = rotn(input.toString(), 21);
		System.out.println("ROT-21: " + rot21);

		String urlDecoded = URLDecoder.decode(rot21);
		System.out.println("URL Decoded: " + urlDecoded);
	}

	/**
	 * Given the constant HEX, swap the nibbles and convert to characters.
	 * @return ASCII text from the HEX data.
	 */
	private static String swapNibblesAndDecodeHex()
	{
		StringBuilder sb1 = new StringBuilder();
		for(String hex : reverse(HEX).split(" "))
		{
			sb1.append((char)Integer.parseInt(hex, 16));
		}
		return sb1.toString();
	}

	/**
	 * Reverse a string.
	 * @param forward
	 * @return drawrof
	 */
	private static String reverse(final String forward)
	{
		StringBuilder reversed = new StringBuilder(forward.length());
		for (char ch : forward.toCharArray())
		{
			reversed.insert(0, ch);
		}
		return reversed.toString();
	}

	/**
	 * Apply the "ROT-n" Ceaser Cipher to the given string. Only applies to alphabetical characters.
	 * @param input input text
	 * @param n amount of places to rotate
	 * @return decoded text.
	 */
	private static String rotn(final String input, final int n)
	{
		StringBuilder sb = new StringBuilder(input.length());
		for (char ch : input.toCharArray())
		{
			if (Character.isLetter(ch))
			{
				if (Character.isUpperCase(ch))
				{
					ch = (char) (((ch - 'A' + n) % 26) + 'A');
				}
				else
				{
					ch = (char) (((ch - 'a' + n) % 26) + 'a');
				}
			}
			sb.append(ch);
		}
		return sb.toString();
	}
}