import java.security.*;

public class JCAPlay {
	/*
     * Converts a byte to hex digit and writes to the supplied buffer
     */
    private static void byte2hex(byte b, StringBuffer buf) {
        char[] hexChars = { '0', '1', '2', '3', '4', '5', '6', '7', '8',
                            '9', 'A', 'B', 'C', 'D', 'E', 'F' };
        int high = ((b & 0xf0) >> 4);
        int low = (b & 0x0f);
        buf.append(hexChars[high]);
        buf.append(hexChars[low]);
    }

    /*
     * Converts a byte array to hex string
     */
    private static String toHexString(byte[] block) {
        StringBuffer buf = new StringBuffer();

        int len = block.length;

        for (int i = 0; i < len; i++) {
             byte2hex(block[i], buf);
             if (i < len-1) {
                 buf.append(":");
             }
        }
        return buf.toString();
    }
	
	public static void main(String[] args) {
		// Create an instance of the random generator
		SecureRandom sr = null;
		try {
			sr = SecureRandom.getInstance("SHA1PRNG");
		} catch(NoSuchAlgorithmException e) {
			e.printStackTrace();
		}

		// Length of the random strings in bytes
		final int NBYTES = 16;
		
		// Declare strings
		byte[] string1 = new byte[NBYTES];
		byte[] string2 = new byte[NBYTES];

		// Generate random strings
		sr.nextBytes(string1);
		System.out.println("string1 = " + toHexString(string1));
		sr.nextBytes(string2);
		System.out.println("string2 = " + toHexString(string2));

		byte[] string = new byte[NBYTES];
		for(int i = 0; i < NBYTES; i++) {
		    string[i] = (byte)(string1[i] ^ string2[i]);
		}
		System.out.println("string = " + toHexString(string));

		// Create an instance of the message digest algorithm
		MessageDigest md = null;
		try {
			md = MessageDigest.getInstance("sHa-1");
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		}
		
		// Hash string1
		byte[] digest1 = md.digest(string1);
		System.out.println(toHexString(digest1));

		// Hash string2
		md.update(string2);
		byte[] digest2 = md.digest();
		System.out.println(toHexString(digest2));

		// Hash string
		for(int i = 0; i < NBYTES; i++) {
		    md.update(string[i]);
		}
		byte[] digest = md.digest();
		System.out.println(toHexString(digest));
	    }
}