Editing Block cipher (section)

===Tweakable block ciphers===
{{Expand section|date=June 2008}}
M. Liskov, R. Rivest, and D. Wagner have described a generalized version of block ciphers called "tweakable" block ciphers.<ref name="tweak">{{cite journal|first1=M.|last1=Liskov|first2=R.|last2=Rivest|first3=D.|last3=Wagner|title=Tweakable Block Ciphers|journal=Crypto 2002|url=http://www.cs.colorado.edu/~jrblack/class/csci7000/f03/papers/tweak-crypto02.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.cs.colorado.edu/~jrblack/class/csci7000/f03/papers/tweak-crypto02.pdf |archive-date=2022-10-09 |url-status=live}}</ref> A tweakable block cipher accepts a second input called the ''tweak'' along with its usual plaintext or ciphertext input. The tweak, along with the key, selects the permutation computed by the cipher. If changing tweaks is sufficiently lightweight (compared with a usually fairly expensive key setup operation), then some interesting new operation modes become possible. The [[disk encryption theory]] article describes some of these modes.