int avPairsLength = avPairs != null ? avPairs.length : 0;
        byte[] temp = new byte[28 + avPairsLength + 4];

        Encdec.enc_uint32le(0x00000101, temp, 0); // Header
        Encdec.enc_uint32le(0x00000000, temp, 4); // Reserved
        Encdec.enc_uint64le(nanos1601, temp, 8);
        System.arraycopy(clientChallenge, 0, temp, 16, 8);