utils.java

Examples using Message Authentication Codes (MACs) and Message Digests

package chapter3;

import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;

import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;

/**
 * General utilities for the third chapter examples.
 */
public class Utils
    extends chapter2.Utils
{
    /**
     * Create a key for use with AES.
     * 
     * @param bitLength
     * @param random
     * @return an AES key.
     * @throws NoSuchAlgorithmException
     * @throws NoSuchProviderException
     */
    public static SecretKey createKeyForAES(
        int          bitLength,
        SecureRandom random)
        throws NoSuchAlgorithmException, NoSuchProviderException
    {
        KeyGenerator generator = KeyGenerator.getInstance("AES", "BC");
        
        generator.init(256, random);
        
        return generator.generateKey();
    }
    
    /**
     * Create an IV suitable for using with AES in CTR mode.
     * <p>
     * The IV will be composed of 4 bytes of message number,
     * 4 bytes of random data, and a counter of 8 bytes.
     * 
     * @param messageNumber the number of the message.
     * @param random a source of randomness
     * @return an initialised IvParameterSpec
     */
    public static IvParameterSpec createCtrIvForAES(
        int             messageNumber,
        SecureRandom    random)
    {
        byte[]          ivBytes = new byte[16];
        
        // initially randomize
        
        random.nextBytes(ivBytes);
        
        // set the message number bytes
        
        ivBytes[0] = (byte)(messageNumber >> 24);
        ivBytes[1] = (byte)(messageNumber >> 16);
        ivBytes[2] = (byte)(messageNumber >> 8);
        ivBytes[3] = (byte)(messageNumber >> 0);
        
        // set the counter bytes to 1
        
        for (int i = 0; i != 7; i++)
        {
            ivBytes[8 + i] = 0;
        }
        
        ivBytes[15] = 1;
        
        return new IvParameterSpec(ivBytes);
    }
    
    /**
     * Convert a byte array of 8 bit characters into a String.
     * 
     * @param bytes the array containing the characters
     * @param length the number of bytes to process
     * @return a String representation of bytes
     */
    public static String toString(
        byte[] bytes,
        int    length)
    {
        char[]	chars = new char[length];
        
        for (int i = 0; i != chars.length; i++)
        {
            chars[i] = (char)(bytes[i] & 0xff);
        }
        
        return new String(chars);
    }
    
    /**
     * Convert a byte array of 8 bit characters into a String.
     * 
     * @param bytes the array containing the characters
     * @return a String representation of bytes
     */
    public static String toString(
        byte[]	bytes)
    {
        return toString(bytes, bytes.length);
    }
    
    /**
     * Convert the passed in String to a byte array by
     * taking the bottom 8 bits of each character it contains.
     * 
     * @param string the string to be converted
     * @return a byte array representation
     */
    public static byte[] toByteArray(
        String string)
    {
        byte[]	bytes = new byte[string.length()];
        char[]  chars = string.toCharArray();
        
        for (int i = 0; i != chars.length; i++)
        {
            bytes[i] = (byte)chars[i];
        }
        
        return bytes;
    }
}