What is a tweakable blockcipher and what does it have to do with OCB?
In its current (but not initial) form, OCB uses the idea of a tweakable blockcipher, described by [Liskov, Rivest, and Wagner] and further developed in [offsets]. In a nutshell, the idea is to design a mode of operation assuming that one has available a blockcipher that depends not only on a key and an input block, but also on a tweak. Later, this “tweakable” blockcipher is instantiated using a conventional blockcipher. Tweaks are arranged to increase monotonically.
