*/
    private byte[] performConstantTimeEncryption(Cipher cipher, byte[] message) throws Exception {
        // Pad to fixed block size to prevent timing leaks
        int blockSize = cipher.getBlockSize();
        if (blockSize == 0)
            blockSize = 16; // GCM mode

        int paddedLength = ((message.length + blockSize - 1) / blockSize) * blockSize;