It's obviously a crypto challenge to anyone who has ever played them. It maps way too nicely to human concepts. This is what every amateur putting together an "alien challenge" without attempting to be scientific about it ends up doing, and it's easy to tell. That's fine if you're doing it for fun, but it's obviously not real.

And that is confirmed:

https://www.popularmechanics.com/space/a19257/nsa-key-to-ext...

I've been here solved that. ACM tried to run an challenge about an "alien computer" that was obviously not alien, but ended up being very real. I was part of the team that reverse engineered it first, but the whole contest collapsed and all interest waned after we ended up finding the very-much-not-alien chip involved by accident. We did cover the initial process, but unfortunately never got around to writing the follow-up posts.

https://fail0verflow.com/blog/2012/unprogramming-intro/ https://web.archive.org/web/20160304030848/http://queue.acm....

It's the Winter 1969 journal, and there Spring/Summer Journals, so I don't necessarily buy the April fools explanation:

https://www.nsa.gov/news-features/declassified-documents/tec...

> Key to The Extraterrestrial Messages - Winter 1969 - Vol. XIV, No. 1

Additionally, that same link above also contains this from the Winter 1966 journal, "Communication with Extraterrestrial Intelligence":

https://www.nsa.gov/Portals/70/documents/news-features/decla...

If aliens were actually found, it definitely wouldn't be announced in an unclassified document shared with everyone at NSA. Although I don't think it's a prank per se, just someone who wrote a cryptography puzzle and wanted to frame it in a cute way.