Java Tutorial/Security/Key Generator

Encryption and Decryption using Symmetric Keys

   <source lang="java">

import java.security.InvalidKeyException; import java.security.Key; import javax.crypto.BadPaddingException; import javax.crypto.Cipher; import javax.crypto.IllegalBlockSizeException; import javax.crypto.KeyGenerator; public class Main {

 static String algorithm = "DESede";
 static Key key = KeyGenerator.getInstance(algorithm).generateKey();
 static Cipher cipher = Cipher.getInstance(algorithm);
 public static void main(String[] args) throws Exception {
   byte[] encryptionBytes = encrypt("input");
   System.out.println("Recovered: " + decrypt(encryptionBytes));
 }
 private static byte[] encrypt(String input) throws InvalidKeyException, BadPaddingException,
     IllegalBlockSizeException {
   cipher.init(Cipher.ENCRYPT_MODE, key);
   byte[] inputBytes = input.getBytes();
   return cipher.doFinal(inputBytes);
 }
 private static String decrypt(byte[] encryptionBytes) throws InvalidKeyException,
     BadPaddingException, IllegalBlockSizeException {
   cipher.init(Cipher.DECRYPT_MODE, key);
   byte[] recoveredBytes = cipher.doFinal(encryptionBytes);
   String recovered = new String(recoveredBytes);
   return recovered;
 }

}</source>

Generate a key for the HMAC-SHA1 keyed-hashing algorithm

   <source lang="java">

import javax.crypto.KeyGenerator; import javax.crypto.SecretKey; public class Main {

 public static void main(String[] argv) throws Exception {
   KeyGenerator keyGen = KeyGenerator.getInstance("HmacMD5");
   SecretKey key = keyGen.generateKey();
   // Generate a key for the HMAC-SHA1 keyed-hashing algorithm
   keyGen = KeyGenerator.getInstance("HmacSHA1");
   key = keyGen.generateKey();
 }

}</source>

Generating a Symmetric Key

   <source lang="java">

import javax.crypto.KeyGenerator; import javax.crypto.SecretKey; public class Main {

 public static void main(String[] argv) throws Exception {
   // Generate a DES key
   KeyGenerator keyGen = KeyGenerator.getInstance("DES");
   SecretKey key = keyGen.generateKey();
   // Generate a Blowfish key
   keyGen = KeyGenerator.getInstance("Blowfish");
   key = keyGen.generateKey();
   // Generate a triple DES key
   keyGen = KeyGenerator.getInstance("DESede");
   key = keyGen.generateKey();
 }

}</source>

Get the bytes of the public and private keys

   <source lang="java">

import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.PrivateKey; import java.security.PublicKey; public class Main {

 public static void main(String[] argv) throws Exception {
   String algorithm = "DSA"; // or RSA, DH, etc.
   // Generate a 1024-bit Digital Signature Algorithm (DSA) key pair
   KeyPairGenerator keyGen = KeyPairGenerator.getInstance(algorithm);
   keyGen.initialize(1024);
   KeyPair keypair = keyGen.genKeyPair();
   PrivateKey privateKey = keypair.getPrivate();
   PublicKey publicKey = keypair.getPublic();
   byte[] privateKeyBytes = privateKey.getEncoded();
   byte[] publicKeyBytes = publicKey.getEncoded();
 }

}</source>

Get the formats of the encoded bytes

   <source lang="java">

import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.PrivateKey; import java.security.PublicKey; public class Main {

 public static void main(String[] argv) throws Exception {
   String algorithm = "DSA"; // or RSA, DH, etc.
   // Generate a 1024-bit Digital Signature Algorithm (DSA) key pair
   KeyPairGenerator keyGen = KeyPairGenerator.getInstance(algorithm);
   keyGen.initialize(1024);
   KeyPair keypair = keyGen.genKeyPair();
   PrivateKey privateKey = keypair.getPrivate();
   PublicKey publicKey = keypair.getPublic();
   String format = privateKey.getFormat(); // PKCS#8
   format = publicKey.getFormat(); // X.509
 }

}</source>

Getting the Bytes of a Generated Symmetric Key

   <source lang="java">

import javax.crypto.KeyGenerator; import javax.crypto.SecretKey; import javax.crypto.spec.SecretKeySpec; public class Main {

 public static void main(String[] argv) throws Exception {
   // Generate a key
   KeyGenerator keyGen = KeyGenerator.getInstance("DESede");
   SecretKey key = keyGen.generateKey();
   // Get the bytes of the key
   byte[] keyBytes = key.getEncoded();
   int numBytes = keyBytes.length;
   // The bytes can be converted back to a SecretKey
   SecretKey key2 = new SecretKeySpec(keyBytes, "DESede");
   boolean b = key.equals(key2); // true
 }

}</source>

Key Generator Demo

   <source lang="java">

import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.NoSuchAlgorithmException; import javax.crypto.KeyGenerator; import javax.crypto.SecretKey; public class MainClass {

 public static void main(String[] args) {
   if (args.length != 2) {
     String err = "Usage: KeyGeneratorApp algorithmName keySize";
     System.out.println(err);
     System.exit(0);
   }
   int keySize = (new Integer(args[1])).intValue();
   SecretKey skey = null;
   KeyPair keys = null;
   String algorithm = args[0];
   try {
     KeyPairGenerator kpg = KeyPairGenerator.getInstance(algorithm);
     kpg.initialize(keySize);
     keys = kpg.genKeyPair();
   } catch (NoSuchAlgorithmException ex1) {
     try {
       KeyGenerator kg = KeyGenerator.getInstance(algorithm);
       kg.init(keySize);
       skey = kg.generateKey();
     } catch (NoSuchAlgorithmException ex2) {
       System.out.println("Algorithm not supported: " + algorithm);
       System.exit(0);
     }
   }
 }

}</source>