There's not much we know about the aliens who sent this. The only thing we know about is that they received the Arecibo Message...and they understood it:




If You Can Raed Tihs, You Msut Be Raelly Smrat

Or, more precisely:

enter image description here
(The "line breaks" are just for visual purposes, nothing in the puzzle indicates a new line)


The text is 700 characters long, so it seems to suggest to split into parts of 7 or 10. If you split it into parts of 10, you'll notice that the sequence 0000000000 appears 7x at the start and the sequence FFFFFFFFFF 5x in the end. (also FFFFFFFFE0 appears 5 and 7 times once) I thought this is a hint that indicates that the solution consists of multiple grids: Either many 7x5 or 5x7 grids. (It turned out to be 5x7 grids) Now convert all hex numbers to binary, pad 0s in front of them until they are 40 characters long (because 40 is the max length of a 10 character hex string converted to binary). Then "fill" each grid with the first 35 characters of the corresponding binary sequence. 0 represents white and 1 represents black (just like in the Arecibo message).

If this is a confusing explanation or you noticed a mistake in my decoding, please let me know and I'll try to improve my answer!

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    $\begingroup$ Nicely done! If you only had the aliens' decoder you might have saved some time with the explanation... but that would have ruined the puzzle, eh. video from the creator, and I have it on authority that's the guy who made it and his voice. :-) $\endgroup$ – HostileFork says dont trust SE Aug 5 '16 at 12:51
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    $\begingroup$ @aÆe I do think it's a very nice encoding. But, as you mentioned in the video, it'll probably primarily be a fun programming / puzzle problem. But who knows, maybe it becomes a real thing sometime :P I 'unfortunately' don't have any ideas for improving the concept, it seems pretty solid to me. $\endgroup$ – user14478 Aug 5 '16 at 14:14

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