For example, when it comes to encryption, it is typically assumed that all messages are the same length. If your application does not make this guarantee, encryption may not provide you with any security. You could wind up in this situation:
https://news.ycombinator.com/item?id=2661890
Think of it this way: asking for a list of tried-and-true crypto solutions is like asking for a list of tried-and-true database schemas. There might be cases where it will work, but for the most part you need to put some thought into what you are doing.