Using BouncyCastle's ChaCha for file encryption

Question

I\'m hoping to encrypt a few files using ChaCha, so I wonder if it\'s appropriate to use Chacha20Poly1305. It seems that this class is designed for TLS, so does that mean it

Answer 1

You can simply use the ChaChaEngine class that is referenced by the Chacha20Poly1305 class. The Engine classes contain implementations of the various cipher classes.

Besides that, the JCA provides a higher level API to work with the various ciphers. So you can also use:

Security.addProvider(new BouncyCastleProvider());
Cipher c = Cipher.getInstance("ChaCha");

After which the normal Java CipherInputStream and CipherOutputStream will become available.

Note that using Poly1305 does provide additional authentication. This is often not a requirement for file encryption, but it does provide an additional layer of security. If you want to have authenticated encryption and you cannot work out how, then please ask a separate question.

Answer 2

You could try something line this:

public void doChaCha(boolean encrypt, InputStream is, OutputStream os,
        byte[] key, byte[] iv) throws IOException {
    CipherParameters cp = new KeyParameter(key);
    ParametersWithIV params = new ParametersWithIV(cp, iv);
    StreamCipher engine = new ChaChaEngine();
    engine.init(encrypt, params);

    byte in[] = new byte[8192];
    byte out[] = new byte[8192];
    int len = 0;
    while(-1 != (len = is.read(in))) {
        len = engine.processBytes(in, 0 , len, out, 0);
        os.write(out, 0, len);
    }
}

public void encChaCha(InputStream is, OutputStream os, byte[] key,
        byte[] iv) throws IOException {
    doChaCha(true, is, os, key, iv);
}

public void decChaCha(InputStream is, OutputStream os, byte[] key,
        byte[] iv) throws IOException {
    doChaCha(false, is, os, key, iv);
}

Note that the ChaChaEngine supports only keys of the length 128 or 256 bits with an IV of 64 bits.

Here is some tests:

@Test
public void chachaText() throws IOException, NoSuchAlgorithmException {
    String text = "chacha.txt";
    Files.write(Paths.get(text), "Hello, World!".getBytes(StandardCharsets.UTF_8), 
        StandardOpenOption.CREATE);
    chacha(text);
}

@Test
public void chachaBin() throws IOException, NoSuchAlgorithmException {
    SecureRandom sr = SecureRandom.getInstanceStrong();
    byte[] data = new byte[1024*1024*4];
    sr.nextBytes(data);
    String bin = "chacha.bin";
    Files.write(Paths.get(bin), data, StandardOpenOption.CREATE);
    chacha(bin);
}

private void chacha(String file) throws NoSuchAlgorithmException, IOException {
    SecureRandom sr = SecureRandom.getInstanceStrong();
    byte[] key = new byte[32]; // 32 for 256 bit key or 16 for 128 bit
    byte[] iv = new byte[8]; // 64 bit IV required by ChaCha20
    sr.nextBytes(key);
    sr.nextBytes(iv);
    String dat = String.format("%s.dat", file);

    try(InputStream is = new FileInputStream(file); 
        OutputStream os = new FileOutputStream(dat)) {
        encChaCha(is, os, key, iv);
    }

    try(InputStream is = new FileInputStream(dat); 
        ByteArrayOutputStream os = new ByteArrayOutputStream()) {
        decChaCha(is, os, key, iv);
        byte[] actual = os.toByteArray();
        byte[] expected = Files.readAllBytes(Paths.get(file));
        Assert.assertArrayEquals(expected, actual);
    }
}

EDIT: encode / decode Strings

@Test
public void chachaString() throws IOException, NoSuchAlgorithmException
{
    String test = "Hello, World!";

    try (InputStream isEnc = new ByteArrayInputStream(test.getBytes(StandardCharsets.UTF_8));
            ByteArrayOutputStream osEnc = new ByteArrayOutputStream())
    {
        SecureRandom sr = SecureRandom.getInstanceStrong();
        byte[] key = new byte[32]; // 32 for 256 bit key or 16 for 128 bit
        byte[] iv = new byte[8]; // 64 bit IV required by ChaCha20
        sr.nextBytes(key);
        sr.nextBytes(iv);

        encChaCha(isEnc, osEnc, key, iv);

        byte[] encoded = osEnc.toByteArray();

        try (InputStream isDec = new ByteArrayInputStream(encoded);
                ByteArrayOutputStream osDec = new ByteArrayOutputStream())
        {
            decChaCha(isDec, osDec, key, iv);

            byte[] decoded = osDec.toByteArray();

            String actual = new String(decoded, StandardCharsets.UTF_8);

            Assert.assertEquals(test, actual);
        }
    }
}

Answer 3

Java 11 adds a "ChaCha20-Poly1305/None/NoPadding" Cipher It is now possible to use without BouncyCastle or some other magic -->

Here´s a reference Implementation:

package chaCha20Poly1305Encryption;

import javax.crypto.*;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.spec.AlgorithmParameterSpec;
import java.util.Base64;

public class ChaCha20Poly1305 {

public static byte[] encrypt(byte[] data, SecretKey key) throws NoSuchPaddingException, NoSuchAlgorithmException,
        InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
    if(key == null) throw new InvalidKeyException("SecretKey must NOT be NULL");

    byte[] nonceBytes = new byte[12];

    // Get Cipher Instance
    Cipher cipher = Cipher.getInstance("ChaCha20-Poly1305/None/NoPadding");

    // Create IvParamterSpec
    AlgorithmParameterSpec ivParameterSpec = new IvParameterSpec(nonceBytes);

    // Create SecretKeySpec
    SecretKeySpec keySpec = new SecretKeySpec(key.getEncoded(), "ChaCha20");

    // Initialize Cipher for ENCRYPT_MODE
    cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivParameterSpec);

    // Perform Encryption
    return cipher.doFinal(data);
}

public static byte[] decrypt(byte[] cipherText, SecretKey key) throws Exception {
    if(key == null) throw new InvalidKeyException("SecretKey must NOT be NULL");
    byte[] nonceBytes = new byte[12];

    // Get Cipher Instance
    Cipher cipher = Cipher.getInstance("ChaCha20-Poly1305/None/NoPadding");

    // Create IvParamterSpec
    AlgorithmParameterSpec ivParameterSpec = new IvParameterSpec(nonceBytes);

    // Create SecretKeySpec
    SecretKeySpec keySpec = new SecretKeySpec(key.getEncoded(), "ChaCha20");

    // Initialize Cipher for DECRYPT_MODE
    cipher.init(Cipher.DECRYPT_MODE, keySpec, ivParameterSpec);

    // Perform Decryption
    return cipher.doFinal(cipherText);
}

public static void main(String[] args) throws Exception {
    SecretKey key = ChaCha20Poly1305KeyGenerator.generateKey();

    String testMessage = "hallo!";
    byte[] encryptedBytes = encrypt(testMessage.getBytes(), key);
    String decryptedMessage = new String(decrypt(encryptedBytes,key));
    System.out.println("testMessage: " + testMessage);
    System.out.println(key.getAlgorithm() + " SecretKey: " + Base64.getEncoder().encodeToString(key.getEncoded()));
    System.out.println("encryptedBytes: " + Base64.getEncoder().encodeToString(encryptedBytes));
    System.out.println("decryptedMessage: "+ decryptedMessage);

}
}

And the corresponding Key-Generator:

package chaCha20Poly1305Encryption;

import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

public class ChaCha20Poly1305KeyGenerator {
    public static SecretKey generateKey() throws NoSuchAlgorithmException {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("ChaCha20");
        //Keysize MUST be 256 bit - as of Java11 only 256Bit is supported
        keyGenerator.init(256);
        return keyGenerator.generateKey();
    }
    public static void main(String[] args) throws NoSuchAlgorithmException {
        SecretKey key = generateKey();
        System.out.println(key.getAlgorithm() + " SecretKey: " + Base64.getEncoder().encodeToString(key.getEncoded()));
    }
}

Code used from my Github GIST: https://gist.github.com/eXspir3/7a0821a6cfdb0495ccc3e69b475a61b9