There are many people with different interests on HN. Startup people, web developers, and even some hardcore cryptographers. While the former will find you article interesting and probably don't already know too much about encryption, the latter will find the article boring and too simple. They probably will complain (maybe even thinking they could have written it better), while the startup people and web devs don't write anything, since HN discourages comments that only state "Good article" or similar.

That's how you end up with an article with lots of upvotes (from the people who liked your artcile) and some rude comments (from the people who didn't like your article).