Android Decryption Error

Question

I am trying to encrypt and decrypt Strings in my Android application but I keep getting an InvalidKeyException error.

Here is my code:

//Generate Keys method

public void generateKeys() {
    Calendar cal = Calendar.getInstance();
    Date now = cal.getTime();
    cal.add(Calendar.YEAR, 25);
    Date end = cal.getTime();

    KeyPairGenerator kpg = null;
    try {
        kpg = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    } catch (NoSuchProviderException e) {
        e.printStackTrace();
    }
    try {
        kpg.initialize(new KeyPairGeneratorSpec.Builder(context)
                .setAlias(KEY_ALIAS)
                .setStartDate(now)
                .setEndDate(end)
                .setSerialNumber(BigInteger.valueOf(1))
                .setSubject(new X500Principal("CN=" + KEY_ALIAS))
                .build());
    } catch (InvalidAlgorithmParameterException e) {
        e.printStackTrace();
    }

    KeyPair kp = kpg.generateKeyPair();

    KeyStore ks = null;
    try {
        ks = KeyStore.getInstance("AndroidKeyStore");
        ks.load(null);
        Enumeration<String> aliases = ks.aliases();
    } catch (KeyStoreException e) {
        e.printStackTrace();
    } catch (CertificateException e) {
        e.printStackTrace();
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    KeyStore.Entry entry = null;
    try {
        entry = ks.getEntry(KEY_ALIAS, null);
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    } catch (UnrecoverableEntryException e) {
        e.printStackTrace();
    } catch (KeyStoreException e) {
        e.printStackTrace();
    }
    if (!(entry instanceof KeyStore.PrivateKeyEntry)) {
        Log.e(LOG_TAG, "Not an instance of PrivateKeyEntry.");
    }
    else{
        privKey = ((KeyStore.PrivateKeyEntry) entry).getPrivateKey();
        pubKey = ((KeyStore.PrivateKeyEntry) entry).getCertificate().getPublicKey();
    }

}

//Encrypt Method

private String encryptString(String value){
    byte[] encodedBytes = null;
    try {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
        cipher.init(Cipher.ENCRYPT_MODE,  pubKey);
        encodedBytes = cipher.doFinal(value.getBytes());
    } catch (Exception e) {
        e.printStackTrace();
    }

    return Base64.encodeToString(encodedBytes, Base64.DEFAULT);
}

//Decrypt Method

private String decryptString(String value){
    byte[] decodedBytes = null;
    try {
        Cipher c = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
        c.init(Cipher.DECRYPT_MODE,  privKey);
        decodedBytes = c.doFinal(Base64.decode(value, Base64.DEFAULT));
    } catch (Exception e) {
        e.printStackTrace();
        Log.e("Error", "Error = " + e);
        return "SECURE_FAILURE";
    }

    return new String(decodedBytes);
}

//Test Code

    generateKeys();
    String encrypted = encryptString("Hello World");
    Log.e("Encrypt", "encrypted = " + encrypted);
    String decrypted = decryptString(encrypted);
    Log.e("Decrypt", "decrypted = " + decrypted);

It looks like the encryption works OK as it prints out something like this:

encrypted = SbA2iWWKQbDL7NTA9xvtjD/viYDdpx9fLRYTSZ8UQzdBy3QLqzkswBY21ErH7FPza3vZys4E4PZw uxaGkRz0aC0FLqsYlbpcJernGm5+D5lRcBOaZmgkNY9pMf0YP75cBbcJdcmb1rDaH40nCRDnEoXv rGESJRqT6p0NMzlZqdd9KO3tqfExwgservAWxPNtRDBbMgE4I/09418jM5Ock5eayfOuv/STwEy6 Ecd56UjFH63h+gP6ed2aMDhBVeExMxvdloY+VnsAxS5Dkoc2GdaljtjRuPK48HQASoJK8EwAMNpz

But when I try to decrypt I get the following error:

java.security.InvalidKeyException: Need RSA private or public key

I can't figure why I am getting this exception? Can anyone help?

Answer 1

this worked for me:

private Cipher getCipher() {
    try {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) { // below android m
            return Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL"); // error in android 6: InvalidKeyException: Need RSA private or public key
        }
        else { // android m and above
            return Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidKeyStoreBCWorkaround"); // error in android 5: NoSuchProviderException: Provider not available: AndroidKeyStoreBCWorkaround
        }
    } catch(Exception exception) {
        throw new RuntimeException("getCipher: Failed to get an instance of Cipher", exception);
    }
}

Answer 2

Try using a different provider, like this:

Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidKeyStoreBCWorkaround");