android - Data decryption in case of modified cipher data

Question

In this example, I am trying to encrypt audio file header and data using CipherOutputStream. I stored the corresponding IV1 to file.
Later, I encrypted the updated header and overwrote the previous cipher data. I stored the corresponding IV2 to file.

I feel the IV1 written to file will no longer useful, because I overwritten the first header cipher data.

On decryption side, by using IV2 I am able to decrypt updated header part only.
I am unable to decrypt the actual data even though I used IV1. It makes sense also. Because, the data that is encrypted using IV1 has been overwritten.

How can I decrypt the data in this scenario? Or am I going completely wrong? Please help?

protected void EncryptAndroid()
{
    byte[] data = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',                
            };
    byte[] header = {'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd',
            'a', 'b', 'c', 'd',};
    byte[] updatedHeader = {'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D',
            'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D'};

    try {
        SecretKey secret = generateKeyAndroid();

        Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, secret);

        AlgorithmParameters params = cipher.getParameters();
        byte[] iv = params.getParameterSpec(IvParameterSpec.class).getIV();

        FileOutputStream os = new FileOutputStream(sdCard.getAbsolutePath() + "/Notes/sample.encrypted");
        CipherOutputStream cos = new CipherOutputStream(os, cipher);

        int offset = 0;
        cos.write(header, offset, 10);
        cos.write(data, offset, 40);

        FileOutputStream ivStream = new FileOutputStream(sdCard.getAbsolutePath() + "/Notes/iv.dat");
        if (ivStream != null) {
            Log.d("Encryption", "Writing iv data to output file");
            ivStream.write(iv);
        }
        ivStream.close();
        cos.close();

        //Create new instance of cipher
        cipher = Cipher.getInstance("AES/CTR/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, secret);

        AlgorithmParameters params1 = cipher.getParameters();
        byte[] iv1 = params1.getParameterSpec(IvParameterSpec.class).getIV();

        //Re open the file to Update the header at starting of the file.
        FileOutputStream os1 = new FileOutputStream(sdCard.getAbsolutePath() + "/Notes/sample.encrypted");
        CipherOutputStream cos1 = new CipherOutputStream(os1, cipher);
        cos1.write(updatedHeader, offset, 10);
        cos1.close();

        FileOutputStream ivStream1 = new FileOutputStream(sdCard.getAbsolutePath() + "/Notes/iv1.dat");
        if (ivStream1 != null) {
            Log.d("Encryption", "Writing iv data to output file");
            ivStream1.write(iv1);
        }
    }catch (Exception e) {
        e.printStackTrace();
    }
}
protected void DecryptAndroid() {
    byte[] hBytes = new byte[10];
    byte[] dBytes = new byte[100];

    try {
        Log.d("Decryption", "Reading iv data ");
        File f1 = new File(sdCard.getAbsolutePath() + "/Notes/iv.dat");
        byte[] newivtext = new byte[(int) f1.length()];
        FileInputStream readivStream = new FileInputStream(sdCard.getAbsolutePath() + "/Notes/iv.dat");
        if (readivStream != null) {
            readivStream.read(newivtext);
        }

        File f2 = new File(sdCard.getAbsolutePath() + "/Notes/iv1.dat");
        byte[] newivtext1 = new byte[(int) f2.length()];
        FileInputStream readivStream1 = new FileInputStream(sdCard.getAbsolutePath() + "/Notes/iv1.dat");
        if (readivStream1 != null) {
            readivStream1.read(newivtext1);
        }

        // The key can also be obtained from the Android Keystore any time as follows:
        KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
        keyStore.load(null);
        SecretKey dsecret = (SecretKey) keyStore.getKey("key2", null);

        // Initialize dcipher
        Cipher dcipher = Cipher.getInstance("AES/CTR/NoPadding");
        dcipher.init(Cipher.DECRYPT_MODE, dsecret,new IvParameterSpec(newivtext1));

        FileInputStream inputStream = new FileInputStream(sdCard.getAbsolutePath() + "/Notes/sample.encrypted");
        FileOutputStream os = new FileOutputStream(sdCard.getAbsolutePath() + "/Notes/sample.decrypted");

        //decrypt header
        int b = inputStream.read(hBytes);
        byte[] dB = new byte[10];
        dB = dcipher.doFinal(hBytes);
        os.write(dB, 0, b);

        // Re-Initialize dcipher
        dcipher = Cipher.getInstance("AES/CTR/NoPadding");
        dcipher.init(Cipher.DECRYPT_MODE, dsecret,new IvParameterSpec(newivtext));
        FileInputStream inputStream1 = new FileInputStream(sdCard.getAbsolutePath() + "/Notes/sample.encrypted");
        inputStream1.skip(10);
        CipherInputStream cis = new CipherInputStream(inputStream1, dcipher);
        b = cis.read(dBytes);
        while (b != -1) {
            Log.d("Decryption", "Bytes decrypted" + b);
            os.write(dBytes, 0, b);
        }
        cis.close();
        os.close();

    } catch (Exception e) {
        e.printStackTrace();
    }
}

Answer 1

Waitting for answers