cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(keybytes, "AES"), new IvParameterSpec(ZERO_IV, 0, ZERO_IV.length));
        if (constant.length != cipher.getBlockSize()) {
            constant = expandNFold(constant, cipher.getBlockSize());
        }
        byte[] enc = constant;
        int klen = keybytes.length;
        byte[] dk = new byte[klen];
        for (int n = 0; n < klen;) {

     */
    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;