[emily37]

Rivest's class is usually described as the "applied crypto" class (I haven't taken it, this is just what I've heard). The "systems security" class is 6.858: http://pdos.csail.mit.edu/6.858/2011/ And there's another class (6.875, taught by Goldwasser or Micali) that is much more pure crypto than Rivest's class. In any case, 6.858 is super fun and probably the most useful for someone looking for practical security knowledge.