Editing Block cipher (section)

===Operations===

====ARX (add–rotate–XOR)====
Many modern block ciphers and hashes are '''ARX''' algorithms—their round function involves only three operations: (A) modular addition, (R) [[circular shift|rotation]] with fixed rotation amounts, and (X) [[exclusive or|XOR]]. Examples include [[ChaCha20]], [[Speck (cipher)|Speck]], [[XXTEA]], and [[BLAKE (hash function)|BLAKE]]. Many authors draw an ARX network, a kind of [[data flow diagram]], to illustrate such a round function.<ref>{{cite book |last1=Aumasson |first1=Jean-Philippe |last2=Bernstein |first2=Daniel J.
|author-link2=Daniel J. Bernstein |chapter=SipHash: a fast short-input PRF |doi=10.1007/978-3-642-34931-7_28 |chapter-url=https://131002.net/siphash/siphash.pdf |editor1-last=Galbraith |editor1-first=Steven |editor2-last=Nandi |editor2-first=Mridul |title=Progress in cryptology-- INDOCRYPT 2012 : 13th International Conference on Cryptology in India, Kolkata, India, December 9-12, 2012, proceedings |date=2012 |publisher=Springer |location=Berlin |isbn=978-3-642-34931-7 |page=494|archive-url=https://web.archive.org/web/20200312053222/https://131002.net/siphash/siphash.pdf |archive-date=2020-03-12 }}</ref>

These ARX operations are popular because they are relatively fast and cheap in hardware and software, their implementation can be made extremely simple, and also because they run in constant time, and therefore are immune to [[timing attack]]s. The [[rotational cryptanalysis]] technique attempts to attack such round functions.

====Other operations====
Other operations often used in block ciphers include data-dependent rotations as in [[RC5]] and [[RC6]], a [[substitution box]] implemented as a [[lookup table]] as in [[Data Encryption Standard]] and [[Advanced Encryption Standard]], a [[permutation box]], and multiplication as in [[IDEA (cipher)|IDEA]].