Video was released very shortly after the incident, very little information was available to the public including to ISIS in the Sinai Province when video was released.
The video could therefore be genuine, maybe we will never know, it does not matter, some facts: officially, when the video was initially released, the authorities discounted the fact that the plane was shot down by a missile but the original message from ISIS did not mention a missile at all, some translations were in fact incorrect, I understand the exact translation is the one below which could indicate a bomb (and not a missile) as it seems to be now the official cause; this means that officially the video has not been declared fake by anybody. It could be indeed very genuine.
In any case the video will not change the fact that this was very likely a bomb in the cargo hold. Very likely bomb was planted by somebody with easy access to the aircraft who was not on board. If a £20 note can let you completely bypass security checks at that airport (proven) imagine what £1,000 can do. Easy, easy, easy.
Message from ISIS was later re-translated as follows (no mention of missile):
“Soldiers of the Caliphate were able to
bring down a Russian plane above Sinai Province with at least 220 Russian crusaders aboard. They were all killed, praise be to God. O Russians, you and your allies take note that you are not safe in Muslims lands or their skies.”
“The killing of dozens daily in Syria with bombs from your planes will bring woe to you. Just as you are killing others, you too will be killed, God willing.”
