Java/Security/Key Generator

Asymmetric Key Maker

  
import java.security.KeyPair;
import java.security.KeyPairGenerator;
public class Main {
  public static void main(String[] args) throws Exception {
    String algorithm = "";
    KeyPair keyPair = KeyPairGenerator.getInstance(algorithm).generateKeyPair();
    System.out.println(keyPair.getPublic());
    System.out.println(keyPair.getPrivate());
  }
}

Generate a 1024-bit RSA key pair

  
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 {
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
    keyGen.initialize(1024);
    KeyPair keypair = keyGen.genKeyPair();
    PrivateKey privateKey = keypair.getPrivate();
    PublicKey publicKey = keypair.getPublic();
  }
}

Generate a 576-bit DH key pair

  
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 {
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DH");
    keyGen.initialize(576);
    KeyPair keypair = keyGen.genKeyPair();
    PrivateKey privateKey = keypair.getPrivate();
    PublicKey publicKey = keypair.getPublic();
  }
}

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

  
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();
  }
}

Generate DSA key pair

  
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.SecureRandom;
public class MainClass {
  public static void main(String[] args) throws Exception {
    KeyPairGenerator kpg = KeyPairGenerator.getInstance("DSA");
    kpg.initialize(1024, new SecureRandom());
    KeyPair dsaKeyPair = kpg.generateKeyPair();
  }
}

Generating a Public/Private Key Pair

  
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 {
    // Generate a 1024-bit Digital Signature Algorithm (DSA) key pair
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
    keyGen.initialize(1024);
    KeyPair keypair = keyGen.genKeyPair();
    PrivateKey privateKey = keypair.getPrivate();
    System.out.println(privateKey);
    PublicKey publicKey = keypair.getPublic();
    System.out.println(publicKey);
  }
}

Generating a Symmetric Key

  
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();
  }
}

Get the bytes of the public and private keys

  
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();
  }
}

Getting the Bytes of a Generated Key Pair

  
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();
  }
}

Key Generator Mac

 
import java.security.Security;
import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
public class MainClass {
  public static void main(String args[]) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    String inputString = "www.jexp.ru";
    KeyGenerator keyGen = KeyGenerator.getInstance("HmacMD5");
    SecretKey secretKey = keyGen.generateKey();
    Mac mac = Mac.getInstance(secretKey.getAlgorithm());
    mac.init(secretKey);
    byte[] byteData = inputString.getBytes("UTF8");
    byte[] macBytes = mac.doFinal(byteData);
    String macAsString = new sun.misc.BASE64Encoder().encode(macBytes);
    System.out.println("Authentication code is: " + macAsString);
  }
}

KeyPair Generator For Private Key

 
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.SecureRandom;
import java.security.Security;
public class MainClass {
  public KeyPair generateKeyPair(long seed)throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("DSA");
    SecureRandom rng = SecureRandom.getInstance("SHA1PRNG", "SUN");
    rng.setSeed(seed);
    keyGenerator.initialize(1024, rng);
    return (keyGenerator.generateKeyPair());
  }
  public static void main(String args[]) throws Exception {
    MainClass kpge = new MainClass();
    KeyPair kp = kpge.generateKeyPair(999);
    System.out.println("\n-- Private Key ----");
    PrivateKey priKey = kp.getPrivate();
    System.out.println("   Algorithm=" + priKey.getAlgorithm());
    System.out.println("   Encoded=" + priKey.getEncoded());
    System.out.println("   Format=" + priKey.getFormat());
  }
}

KeyPair Generator For Public Key

 
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Security;
public class MainClass {
  public KeyPair generateKeyPair(long seed)throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("DSA");
    SecureRandom rng = SecureRandom.getInstance("SHA1PRNG", "SUN");
    rng.setSeed(seed);
    keyGenerator.initialize(1024, rng);
    return (keyGenerator.generateKeyPair());
  }
  public static void main(String args[]) throws Exception {
    MainClass kpge = new MainClass();
    KeyPair kp = kpge.generateKeyPair(999);
    System.out.println("-- Public Key ----");
    PublicKey pubKey = kp.getPublic();
    System.out.println("   Algorithm=" + pubKey.getAlgorithm());
    System.out.println("   Encoded=" + pubKey.getEncoded());
    System.out.println("   Format=" + pubKey.getFormat());
  }
}

The bytes can be converted back to public and private key objects

  
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.EncodedKeySpec;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
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();
    
    KeyFactory keyFactory = KeyFactory.getInstance(algorithm);
    EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(privateKeyBytes);
    PrivateKey privateKey2 = keyFactory.generatePrivate(privateKeySpec);
    EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyBytes);
    PublicKey publicKey2 = keyFactory.generatePublic(publicKeySpec);
    // The orginal and new keys are the same
    boolean same = privateKey.equals(privateKey2); 
    same = publicKey.equals(publicKey2); 
  }
}

Using the KeyGenerator class and showing how to create a SecretKeySpec from an encoded key

 
import java.security.Key;
import java.security.Security;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
/**
 * Basic example using the KeyGenerator class and showing how to create a
 * SecretKeySpec from an encoded key.
 */
public class MainClass {
  public static void main(String[] args) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());        
    byte[] input = "www.jexp.ru".getBytes();
    
    byte[] ivBytes = new byte[] { 0x00, 0x00, 0x00, 0x01, 0x04, 0x05, 0x06, 0x07, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x01 };
    Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
    KeyGenerator generator = KeyGenerator.getInstance("AES", "BC");
    generator.init(192);
    Key encryptionKey = generator.generateKey();
    System.out.println("key   : " + Utils.toHex(encryptionKey.getEncoded()));
    System.out.println("input : " + new String(input));
    // encryption pass
    cipher.init(Cipher.ENCRYPT_MODE, encryptionKey, new IvParameterSpec(ivBytes));
    byte[] cipherText = new byte[cipher.getOutputSize(input.length)];
    int ctLength = cipher.update(input, 0, input.length, cipherText, 0);
    ctLength += cipher.doFinal(cipherText, ctLength);
    // decryption pass
    Key decryptionKey = new SecretKeySpec(encryptionKey.getEncoded(), encryptionKey.getAlgorithm());
    cipher.init(Cipher.DECRYPT_MODE, decryptionKey, new IvParameterSpec(ivBytes));
    byte[] plainText = new byte[cipher.getOutputSize(ctLength)];
    int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0);
    ptLength += cipher.doFinal(plainText, ptLength);
    System.out.println("plain : " + new String(plainText) + " bytes: " + ptLength);
  }
}

class Utils
{
    private static String digits = "0123456789abcdef";
    
    /**
     * Return length many bytes of the passed in byte array as a hex string.
     * 
     * @param data the bytes to be converted.
     * @param length the number of bytes in the data block to be converted.
     * @return a hex representation of length bytes of data.
     */
    public static String toHex(byte[] data, int length)
    {
        StringBuffer  buf = new StringBuffer();
        
        for (int i = 0; i != length; i++)
        {
            int v = data[i] & 0xff;
            
            buf.append(digits.charAt(v >> 4));
            buf.append(digits.charAt(v & 0xf));
        }
        
        return buf.toString();
    }
    
    /**
     * Return the passed in byte array as a hex string.
     * 
     * @param data the bytes to be converted.
     * @return a hex representation of data.
     */
    public static String toHex(byte[] data)
    {
        return toHex(data, data.length);
    }
}

Wrap And Unwrap Key

 
import java.security.Key;
import java.security.Security;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.spec.SecretKeySpec;
public class MainClass {
  public static void main(String[] args) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());    
    KeyGenerator generator = KeyGenerator.getInstance("AES", "BC");
    generator.init(128);
    Key keyToBeWrapped = generator.generateKey();
    System.out.println("input    : " + new String(keyToBeWrapped.getEncoded()));
    // create a wrapper and do the wrapping
    Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding", "BC");
    KeyGenerator keyGen = KeyGenerator.getInstance("AES", "BC");
    keyGen.init(256);
    Key wrapKey = keyGen.generateKey();
    cipher.init(Cipher.ENCRYPT_MODE, wrapKey);
    byte[] wrappedKey = cipher.doFinal(keyToBeWrapped.getEncoded());
    System.out.println("wrapped  : " + new String(wrappedKey));
    // unwrap the wrapped key
    cipher.init(Cipher.DECRYPT_MODE, wrapKey);
    Key key = new SecretKeySpec(cipher.doFinal(wrappedKey), "AES");
    System.out.println("unwrapped: " + new String(key.getEncoded()));
  }
}