Java IO.pdf - Nguyen Dang Binh

Example 10.7. FileDecryptor
import java.io.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
public class FileDecryptor {
public static void main(String[] args) {
if (args.length != 3) {
System.err.println("Usage: java FileDecryptor infile outfile
password");
return;
}
String infile = args[0];
String outfile = args[1];
String password = args[2];
if (password.length() < 8 ) {
System.err.println("Password must be at least eight characters
long");
}
try {
FileInputStream fin = new FileInputStream(infile);
FileOutputStream fout = new FileOutputStream(outfile);
// Create a key.
byte[] desKeyData = password.getBytes();
DESKeySpec desKeySpec = new DESKeySpec(desKeyData);
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
SecretKey desKey = keyFactory.generateSecret(desKeySpec);
// Read the initialization vector.
DataInputStream din = new DataInputStream(fin);
int ivSize = din.readInt();
byte[] iv = new byte[ivSize];
din.readFully(iv);
IvParameterSpec ivps = new IvParameterSpec(iv);
// Use Data Encryption Standard.
Cipher des = Cipher.getInstance("DES/CBC/PKCS5Padding");
des.init(Cipher.DECRYPT_MODE, desKey, ivps);
byte[] input = new byte[64];
while (true) {
int bytesRead = fin.read(input);
if (bytesRead == -1) break;
byte[] output = des.update(input, 0, bytesRead);
if (output != null) fout.write(output);
}
byte[] output = des.doFinal();
if (output != null) fout.write(output);
fin.close();
fout.flush();
fout.close();
Java I/O
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