Encrypt and decrypt string using ChaCha20

Question

I want to decrypt and encrypt a string using chacha20

BouncyCastleProvider is using chacha20 technique. So I included it jar. and tried the code but not able to work.

PBE.java

public class PBE extends AppCompatActivity {

    private static final String salt = "A long, but constant phrase that will be used each time as the salt.";
    private static final int iterations = 2000;
    private static final int keyLength = 256;
    private static final SecureRandom random = new SecureRandom();

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.pbe);

        try {
            Security.insertProviderAt(new BouncyCastleProvider(), 1);
            //Security.addProvider(new BouncyCastleProvider());

            String passphrase = "The quick brown fox jumped over the lazy brown dog";
            String plaintext = "Hello";
            byte [] ciphertext = encrypt(passphrase, plaintext);
            String recoveredPlaintext = decrypt(passphrase, ciphertext);

            TextView decryptedTv = (TextView) findViewById(R.id.tv_decrypt);

            decryptedTv.setText(recoveredPlaintext);

            System.out.println(recoveredPlaintext);
        }catch (Exception e){
            e.printStackTrace();
        }

    }

    private static byte [] encrypt(String passphrase, String plaintext) throws Exception {
        SecretKey key = generateKey(passphrase);

        Cipher cipher = Cipher.getInstance("AES/CTR/NOPADDING");//,new BouncyCastleProvider());
        cipher.init(Cipher.ENCRYPT_MODE, key, generateIV(cipher), random);
        return cipher.doFinal(plaintext.getBytes());
    }

    private static String decrypt(String passphrase, byte [] ciphertext) throws Exception {
        SecretKey key = generateKey(passphrase);

        Cipher cipher = Cipher.getInstance("AES/CTR/NOPADDING");// , new BouncyCastleProvider());
        cipher.init(Cipher.DECRYPT_MODE, key, generateIV(cipher), random);
        return new String(cipher.doFinal(ciphertext));
    }

    private static SecretKey generateKey(String passphrase) throws Exception {
        PBEKeySpec keySpec = new PBEKeySpec(passphrase.toCharArray(), salt.getBytes(), iterations, keyLength);
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWITHSHA256AND256BITAES-CBC-BC");
        return keyFactory.generateSecret(keySpec);
    }

    private static IvParameterSpec generateIV(Cipher cipher) throws Exception {
        byte [] ivBytes = new byte[cipher.getBlockSize()];
        random.nextBytes(ivBytes);
        return new IvParameterSpec(ivBytes);
    }

}

But it is not giving me proper result..

Edit and Updated Code

public class ChaCha20Encryptor implements Encryptor {

    private final byte randomIvBytes[] = {0, 1, 2, 3, 4, 5, 6, 7};

    static {
        Security.addProvider(new BouncyCastleProvider());
    }

    @Override
    public byte[] encrypt(byte[] data, byte[] randomKeyBytes) throws IOException, InvalidKeyException,
            InvalidAlgorithmParameterException, InvalidCipherTextException {

        ChaChaEngine cipher = new ChaChaEngine();
        CipherParameters cp = new KeyParameter(getMyKey(randomKeyBytes));
        cipher.init(true, new ParametersWithIV(cp , randomIvBytes));
        //cipher.init(true, new ParametersWithIV(new KeyParameter(randomKeyBytes), randomIvBytes));

        byte[] result = new byte[data.length];
        cipher.processBytes(data, 0, data.length, result, 0);
        return result;
    }

    @Override
    public byte[] decrypt(byte[] data, byte[] randomKeyBytes)
            throws InvalidKeyException, InvalidAlgorithmParameterException, IOException,
            IllegalStateException, InvalidCipherTextException {

        ChaChaEngine cipher = new ChaChaEngine();
        CipherParameters cp = new KeyParameter(getMyKey(randomKeyBytes));
        cipher.init(false, new ParametersWithIV(cp , randomIvBytes));
        //cipher.init(false, new ParametersWithIV(new KeyParameter(randomKeyBytes), randomIvBytes));

        byte[] result = new byte[data.length];
        cipher.processBytes(data, 0, data.length, result, 0);
        return result;
    }

    @Override
    public int getKeyLength() {
        return 32;
    }

    @Override
    public String toString() {
        return "ChaCha20()";
    }

    private static byte[] getMyKey(byte[] key){
        try {
            //byte[] key = encodekey.getBytes("UTF-8");
            MessageDigest sha = MessageDigest.getInstance("SHA-1");
            key = sha.digest(key);
            key = Arrays.copyOf(key, 16); // use only first 128 bit
        }
        catch (NoSuchAlgorithmException e){
            e.printStackTrace();
        }
        return key;
    }
}

Now I have only problem decrypting. It shows an error that key must be 128 or 256 bits. What am I doing wrong.

Answer 1

The output of a cipher consists of random bits (generally limited by implementations to 8-bit bytes). Random bytes are likely to contain invalid characters in any character set. If you require a String, encode the ciphertext to base 64.

Furthermore, you re-generate the IV on decrypt. IV during encryption/decryption should match.