Android Keystore Error “could not generate key in keystore”

public class EncryptionApi18AndAbove{
    private Context context;
    private KeyStore keyStore;
    private static String alias = "alias";

    public EncryptionApi18AndAbove(Context context) {
        this.context = context;
        try {
            keyStore = KeyStore.getInstance("AndroidKeyStore");
            keyStore.load(null);
        } catch (Exception e) {
           // bla bla
        }
    }

    private String createNewKeys(String alias, Context context) {
        try {
            if (!keyStore.containsAlias(alias)) {
                Calendar start = Calendar.getInstance();
                Calendar end = Calendar.getInstance();
                end.add(Calendar.YEAR, 1);
                KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(context)
                        .setAlias(alias)
                        .setSubject(new X500Principal("CN=Sample Name, O=Android Authority"))
                        .setSerialNumber(BigInteger.ONE)
                        .setStartDate(start.getTime())
                        .setEndDate(end.getTime())
                        .build();
                KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
                generator.initialize(spec);
                generator.initialize(spec);
                generator.generateKeyPair();
            }
        } catch (Exception e) {
            //bla bla
        }
        return alias;
    }

    @Override
    public String encrypt(String text) {
        if (text == null || text.length() == 0) {
            return text;
        }
        try {
            KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry) keyStore.getEntry(createNewKeys(alias, context), null);
            PublicKey publicKey = privateKeyEntry.getCertificate().getPublicKey();
            Cipher inCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
            inCipher.init(Cipher.ENCRYPT_MODE, publicKey);

            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
            CipherOutputStream cipherOutputStream = new CipherOutputStream(
                    outputStream, inCipher);
            cipherOutputStream.write(text.getBytes("UTF-8"));
            cipherOutputStream.close();

            return Base64.encodeToString(outputStream.toByteArray(), Base64.DEFAULT);
        } catch (Exception e) {
            //bla bla
        }
        return text;
    }

    @Override
    public String decrypt(String text) {
        if (text == null || text.length() == 0) {
            return text;
        }
        try {
            KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry) keyStore.getEntry(createNewKeys(alias, context), null);
            PrivateKey privateKey = privateKeyEntry.getPrivateKey();

            Cipher output = Cipher.getInstance("RSA/ECB/PKCS1Padding");
            output.init(Cipher.DECRYPT_MODE, privateKey);

            CipherInputStream cipherInputStream = new CipherInputStream(
                    new ByteArrayInputStream(Base64.decode(text, Base64.DEFAULT)), output);
            ArrayList<Byte> values = new ArrayList<>();
            int nextByte;
            while ((nextByte = cipherInputStream.read()) != -1) {
                values.add((byte) nextByte);
            }
            byte[] bytes = new byte[values.size()];
            for (int i = 0; i < bytes.length; i++) {
                bytes[i] = values.get(i).byteValue();
            }
            return new String(bytes, 0, bytes.length, "UTF-8");

        } catch (Exception e) {
            // bla bla
        }
        return text;
    }
}

You can use this class . This is works min SDK 18 and above. You can create Android Keystore key , decrypt and encrypt simple text.