MainClass.java Source code

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Here is the source code for MainClass.java

Source

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);
    }
}