Hex.java

package org.nick.passman;

public class Hex {

    private Hex() {
    }

    public static byte[] fromHex(String digits) {
        digits = digits.trim().replaceAll(" ", "");
        final int bytes = digits.length() / 2;
        if (2 * bytes != digits.length()) {
            throw new IllegalArgumentException(
                    "Hex string must have an even number of digits");
        }

        byte[] result = new byte[bytes];
        for (int i = 0; i < digits.length(); i += 2) {
            result[i / 2] = (byte) Integer.parseInt(digits.substring(i, i + 2),
                    16);
        }

        return result;
    }

    public static String toHex(byte[] bytes) {
        StringBuilder buff = new StringBuilder();
        for (byte b : bytes) {
            buff.append(String.format("%02X", b));
        }

        return buff.toString();
    }
}