To add on to this, it is of course necessary to have enough familiarity and competence with the basic principles of cryptography to know that you're "doing what everyone else is doing" correctly, instead of just some silly pantomime, such as: http://thedailywtf.com/Articles/Topgrade,-SHA1-Encryption.as...

But it's not necessary to understand the depths of cryptography beyond that there are various black boxes that have certain properties.