Editing Cryptanalysis (section)

===Amount of information available to the attacker===
{{main|Attack model}}
[[Attack model|Cryptanalytical attacks]] can be classified based on what type of information the attacker has available. As a basic starting point it is normally assumed that, for the purposes of analysis, the general [[algorithm]] is known; this is [[Claude Shannon|Shannon's Maxim]] "the enemy knows the system"<ref>{{cite journal|last1=Shannon|first1=Claude|title=Communication Theory of Secrecy Systems|journal=Bell System Technical Journal|date=4 October 1949|volume=28|issue=4|page=662|doi=10.1002/j.1538-7305.1949.tb00928.x|url=https://archive.org/stream/bstj28-4-656#page/n5/mode/2up|access-date=20 June 2014|ref=Shannon}}</ref> – in its turn, equivalent to [[Kerckhoffs's principle]].<ref>{{citation |first = David |last = Kahn |title = The Codebreakers: the story of secret writing  |year = 1996 |edition=second |publisher = Scribners |page=235}}</ref> This is a reasonable assumption in practice – throughout history, there are countless examples of secret algorithms falling into wider knowledge, variously through [[espionage]], [[betrayal]] and [[reverse engineering]]. (And on occasion, ciphers have been broken through pure deduction; for example, the German [[Lorenz cipher]] and the Japanese [[Purple code]], and a variety of classical schemes):<ref>{{cite book|author=Schmeh, Klaus|title=Cryptography and public key infrastructure on the Internet|publisher=John Wiley & Sons|year=2003|isbn=978-0-470-84745-9|page=45|url=https://books.google.com/books?id=9NqidkUqHdgC&pg=PA45}}</ref>
* ''[[Ciphertext-only attack|Ciphertext-only]]'': the cryptanalyst has access only to a collection of [[ciphertext]]s or [[codetext]]s.
* ''[[Known-plaintext attack|Known-plaintext]]'': the attacker has a set of ciphertexts to which they know the corresponding [[plaintext]].
* ''[[Chosen plaintext attack|Chosen-plaintext]]'' (''[[chosen-ciphertext attack|chosen-ciphertext]]''): the attacker can obtain the ciphertexts (plaintexts) corresponding to an arbitrary set of plaintexts (ciphertexts) of their own choosing.
* ''[[Adaptive chosen plaintext attack|Adaptive chosen-plaintext]]'': like a chosen-plaintext attack, except the attacker can choose subsequent plaintexts based on information learned from previous encryptions, similarly to the ''[[Adaptive chosen ciphertext attack]]''.
* ''[[Related-key attack]]'': Like a chosen-plaintext attack, except the attacker can obtain ciphertexts encrypted under two different keys. The keys are unknown, but the relationship between them is known; for example, two keys that differ in the one bit.