Andy LoPresto reposted this 2013 gem from Pinboard’s blog:

There is no difference, from the attacker’s point of view, between gross and tiny errors. Both of them are equally exploitable. In at least three [of the Matasano Crypto Challenges], the mere fact of getting distinguishable error messages was enough to recover the entire message.

This lesson is very hard to internalize. In the real world, if you build a bookshelf and forget to tighten one of the screws all the way, it does not burn down your house.