Source Code : Message without tampering with MAC (DES), encryption AES in CTR mode

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Message without tampering with MAC (DES), encryption AES in CTR mode

     
import java.security.Key;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.security.Security;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.bouncycastle.jce.provider.BouncyCastleProvider;

/**
 * Message without tampering with MAC (DES), encryption AES in CTR mode
 */
public class MainClass {
  public static void main(String[] args) throws Exception {
    Security.addProvider(new BouncyCastleProvider());        
    SecureRandom random = new SecureRandom();
    IvParameterSpec ivSpec = createCtrIvForAES(1, random);
    Key key = createKeyForAES(256, random);
    Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
    String input = "www.java2s.com";
    Mac mac = Mac.getInstance("DES", "BC");
    byte[] macKeyBytes = "12345678".getBytes();
    Key macKey = new SecretKeySpec(macKeyBytes, "DES");
    System.out.println("input : " + input);

    // encryption step
    cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);
    byte[] cipherText = new byte[cipher.getOutputSize(input.length() + mac.getMacLength())];
    int ctLength = cipher.update(input.getBytes(), 0, input.length(), cipherText, 0);
    mac.init(macKey);
    mac.update(input.getBytes());
    ctLength += cipher.doFinal(mac.doFinal(), 0, mac.getMacLength(), cipherText, ctLength);
    System.out.println("cipherText : " + new String(cipherText));
    
    // decryption step
    cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);
    byte[] plainText = cipher.doFinal(cipherText, 0, ctLength);
    int messageLength = plainText.length - mac.getMacLength();

    mac.init(macKey);
    mac.update(plainText, 0, messageLength);

    byte[] messageHash = new byte[mac.getMacLength()];
    System.arraycopy(plainText, messageLength, messageHash, 0, messageHash.length);

    System.out.println("plain : " + new String(plainText) + " verified: "
        + MessageDigest.isEqual(mac.doFinal(), messageHash));
  }

  static SecretKey createKeyForAES(int bitLength, SecureRandom random)
      throws NoSuchAlgorithmException, NoSuchProviderException {
    KeyGenerator generator = KeyGenerator.getInstance("AES", "BC");
    generator.init(256, random);
    return generator.generateKey();
  }

  public static IvParameterSpec createCtrIvForAES(int messageNumber, SecureRandom random) {
    byte[] ivBytes = new byte[16];
    random.nextBytes(ivBytes);
    ivBytes[0] = (byte) (messageNumber >> 24);
    ivBytes[1] = (byte) (messageNumber >> 16);
    ivBytes[2] = (byte) (messageNumber >> 8);
    ivBytes[3] = (byte) (messageNumber >> 0);
    for (int i = 0; i != 7; i++) {
      ivBytes[8 + i] = 0;
    }
    ivBytes[15] = 1;
    return new IvParameterSpec(ivBytes);
  }
}

           
         
    
    
    
    
  

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