Sorry for not following your comments carefully.

No, there was no authentication that I am aware of. When the FBI introduced it in the Moussaoui trial, there was no objection from the defense and there is no mention of its authentication in the court transcript, though it may be a court protocol that I am unaware of.

why bother for an authentication?

Just kidding. Or not?

"There was no doubt of bin Laden's responsibility for the September 11 attacks before the tape was discovered," said Secretary of Defense Donald H. Rumsfeld.

http://www.defenselink.mil/releases/release.aspx?releaseid=3184

I suppose there is no way to prove the origin/authentification or if this is the real Bin Laden.
But what we could prove is the lousy translation.

German magazine Monitor tried to prove the translation right, not the origin, and did not fall for reassuring. The results were devastating

Almost always left out of these discussions is the misleading translation provided by the State Department. The OBL of this video speaks of "they" and "them" doing 9/11, not "us" and "we." The translation was provided in less than 10 hours by translators who later complained about the rush job. German TV journalist Ekkehard Siekker (Monitor/ARD) hired translators who worked on it for more than 30 hours before giving up on the inaudibles and calling the State Dept's freelancers to find out how they had arrived at their results - that was when the latter said, well, if you had 30 you'll know better than us!
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&add...

There were other flaws, the "Bin Laden" did not say "in advance" nor
German text archieved:
http://web.archive.org/web/20021218105636/www.wdr.de/tv/monitor/beitraeg...
English translation:
http://dc.indymedia.org/newswire/display/16801

Another take by infowars:
http://www.infowars.net/articles/february2007/190207Osama_tape.htm

BTW: Monitors Siekker never worked again for Monitor.

Here's the Jack Riddlers take:

1) It's not the same guy. As stickdog says, a matter of basic facial recognition skills. Argue away; it doesn't look like the same guy because it's not the same guy. Unless you're having serious cognitive dissonance issues, or you're determined to always pitch the official story, it's obvious that it's not the same guy, and it's been obvious all along. This is the clear "default hypothesis." Only someone who privileges official spin over their own lying eyes can convince themselves otherwise.

2) That being said, the guy could be anyone. The video could have been produced by anyone. The guy could be one of Osama's hired doubles. The video could be a fake produced by the Russians, or the Northern Alliance (who supposedly found it first), or pretty much any agency, or, for that matter, amateurs. It's not like the production values are hard to meet (even in Afghanistan). As an aside, the official story (I hope I'm getting it right) is that the video was made in Kandahar around Nov. 15, though it was found in Jalalabad in early Dec. Both cities were under siege at that time...

3) This video is significant because the USG grabbed it with every tentacle and announced it was significant. Though it's unlikely the CIA produced the video, the USG began committing an act of fraud from the moment it announced the video was genuine and significant.

4) That fraud extended to a fraudulent translation, designed to create the impression of a confession. I've met the TV author Ekkehard Siekker and had the privilege of co-organizing public appearances with him. In his report for Monitor (ARD), he had Arab translators produce a rendering. After 30 hours, they called the State Dept. translators with some questions. And they discovered that the State Dept. translators had been given only 10 hours to produce their work, and that they knew much less about it.

5) The State Dept. version falsely turned third person statements of being happy about the attacks into first-person claims of authorship. In a later transcript, the "Osama" even begins to mention the names of specific alleged hijackers.

So. The question of who made the video is completely irrelevant. It's not Osama. The guy in the video does not directly confess to authorship of the 9/11 attacks. But the US Government has presented this largely inaudible work as proof of Osama's authorship. That is an act of fraud. One of many. And quite indicative - they don't have anything better to go with, do they? Remember, this was the first few months. The period of the promised Powell "white paper" that never materialized. Of the Blair memo that filled in, which didn't actually make a case that al Qaeda was behind the attacks. Of revelation after revelation that the official story was full of holes.

http://www.democraticunderground.com/discuss/duboard.php?az=send_mesg&u_...

point 2 reminds me that it should was a sting op, here it is
http://www.muckrakerreport.com/id301.html
A must read!

If you digg a little deeper in regards to the release all the newer Al Qaida or "Bin Laden" tapes, it really gets interesting. Hints: SITE, Intel-Center.
There even was a showing in front of the european parlament with a totally fabricated Osama confession after an alleged atomic dirty bomb went off in Brussels europe- with alle media headlines and reports faked, too. What a pity that they won't show us.

For making up false messages in the digital age the documentary " Zero" by Ghioletto Chiesa does contain an outstandig interesting scene about a large anti-terror exercise, which was conducted in 2004 and in which the European parliament and NATO participated and was led by the CIA near Washington Center for the Strategic and Internationally Studies (CSIS) direction. In the center of the large-scale maneuver was the scenario of the ignition of an dirty atomic bomb, located in Brussels. In the course of the exercise the baffled European Union parliamentarians saw a confession video of Bin Laden on large canvas to the news of the first coordinated atomic terror attack in the world. The fictitious pictorial material differed in nothing from the known productions, which are presented to the whole world since 11 September every few months in the regular television messages and on those allegedly the real bad guys were presented.