This is HN, surely someone can point me in the right direction to learn more about the specific part of MD5 that makes it weak to this, even if it is only conceptual.

Try: https://ad-pdf.s3.amazonaws.com/papers/wp.MD5_Collisions.en_...

(snark: this is the 8th Google search result for "learn more about the specific part of MD5 that makes it weak")

>this isn't something that was supposed to be easy

Parent to the comment you are replying to said that it wasn't hard. If it's not hard then it ought to be quite easy.

What I meant is that when md5 was designed, it was supposed to make this thing difficult.

However flaws in the design have made this easy.

Ah, I see :)