Java Cryptography

Hello, zoT1wy1njA0=!

Let’s jump right into Java cryptography with some examples. The first example can be run by anyone who has the Java Development Kit (JDK) 1.1 or later installed. The second example uses classes from the Java Cryptography Extension (JCE). To run it, you will need to download and install the JCE, which is available in the United States and Canada only at http://java.sun.com/products/jdk/1.2/jce/. Chapter 3, discusses these pieces of software and how they fit together.

Don’t worry if you don’t understand everything in these programs. They are demonstrations of what you can do with cryptography in Java, and everything in them will be explained in more detail elsewhere in the book.

Masher

Our first example demonstrates how a message digest works. A message digest takes an arbitrary amount of input data and creates a short, digested version of the data, sometimes called a digital fingerprint, secure hash, or cryptographic hash. Chapter 2 and Chapter 6 contain more detail about message digests. This program creates a message digest from a file:

import java.io.*; import java.security.*; import sun.misc.*; public class Masher { public static void main(String[] args) throws Exception { // Check arguments. if (args.length != 1) { System.out.println("Usage: Masher filename"); return; } // Obtain a message digest object. MessageDigest md = MessageDigest.getInstance("MD5"); // Calculate the digest for the given file. FileInputStream in = new FileInputStream(args[0]); byte[] buffer ...