Editing Ciphertext (section)

== Cryptanalysis ==
[[Image:Zimmermann-telegramm-offen.jpg|thumb|250px|right|The [[Zimmermann Telegram]] decrypted into plaintext (and translated into English).]]
{{Main|Cryptanalysis}}
Cryptanalysis (also referred to as codebreaking or [[Password cracking|cracking the code]]) is the study of applying various methodologies to obtain the meaning of encrypted information, without having access to the cipher required to correctly decrypt the information. This typically involves gaining an understanding of the system design and determining the cipher. 

Cryptanalysts can follow one or more [[attack model]]s to crack a cipher, depending upon what information is available and the type of cipher being analyzed. Ciphertext is generally the most easily obtained part of a [[cryptosystem]] and therefore is an important part of cryptanalysis. 

=== Attack models ===
* [[Ciphertext-only attack|Ciphertext-only]]: the cryptanalyst has access only to a collection of ciphertexts or code texts. This is the weakest attack model because the cryptanalyst has limited information. Modern ciphers rarely fail under this attack.<ref>{{cite book |last=Schneier |first=Bruce |url=https://archive.org/details/secretsliesdigit00schn/page/90 |title=Secrets & Lies |date=28 August 2000 |publisher=Wiley Computer Publishing Inc |isbn=0-471-25311-1 |pages=[https://archive.org/details/secretsliesdigit00schn/page/90 90–91]}}</ref>
* [[Known-plaintext attack|Known-plaintext]]: the attacker has a set of ciphertexts to which they know the corresponding plaintext
* [[Chosen-plaintext attack]]: the attacker can obtain the ciphertexts corresponding to an arbitrary set of plaintexts of their own choosing
** Batch chosen-plaintext attack: where the cryptanalyst chooses all plaintexts before any of them are encrypted. This is often the meaning of an unqualified use of "chosen-plaintext attack".
** Adaptive chosen-plaintext attack: where the cryptanalyst makes a series of interactive queries, choosing subsequent plaintexts based on the information from the previous encryptions.
* [[Chosen-ciphertext attack]]: the attacker can obtain the plaintexts corresponding to an arbitrary set of ciphertexts of their own choosing
** [[Adaptive chosen-ciphertext attack]]
** [[Indifferent chosen-ciphertext attack]]
* [[Related-key attack]]: similar to 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 (e.g., two keys that differ in the one bit).