Cryptanalysis

cryptanalystcodebreakingcodebreakercryptanalystscodebreakerscryptanalyticcode-breakingcode breakingcryptanalytic attackcryptoanalysis
Cryptanalysis (from the Greek kryptós, "hidden", and analýein, "to loosen" or "to untie") is the study of analyzing information systems in order to study the hidden aspects of the systems.wikipedia
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Claude Shannon

Claude E. ShannonShannonClaude Elwood Shannon
Shannon contributed to the field of cryptanalysis for national defense during World War II, including his fundamental work on codebreaking and secure telecommunications.

Cryptography

cryptographiccryptographercryptology
Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.
Cryptanalysis is the term used for the study of methods for obtaining the meaning of encrypted information without access to the key normally required to do so; i.e., it is the study of how to crack encryption algorithms or their implementations.

Algorithm

algorithmsalgorithm designcomputer algorithm
Arabic mathematicians such as Al-Kindi in the 9th century used cryptographic algorithms for code-breaking, based on frequency analysis.

Known-plaintext attack

cribcribsknown plaintext
The known-plaintext attack (KPA) is an attack model for cryptanalysis where the attacker has access to both the plaintext (called a crib), and its encrypted version (ciphertext).

Ciphertext-only attack

Ciphertext-onlyciphertext-only scenariocipher-text only
In cryptography, a ciphertext-only attack (COA) or known ciphertext attack is an attack model for cryptanalysis where the attacker is assumed to have access only to a set of ciphertexts.

Lorenz cipher

TunnyLorenz SZ 40/42Lorenz
In World War II, the Allies benefitted enormously from their joint success cryptanalysis of the German ciphers — including the Enigma machine and the Lorenz cipher — and Japanese ciphers, particularly 'Purple' and JN-25.
British cryptanalysts, who referred to encrypted German teleprinter traffic as Fish, dubbed the machine and its traffic Tunny (meaning tunafish) and deduced its logical structure three years before they saw such a machine.

Espionage

spysecret agentspies
Codebreaking (cryptanalysis or COMINT), aircraft or satellite photography, (IMINT) and research in open publications (OSINT) are all intelligence gathering disciplines, but none of them is considered espionage.

Chosen-plaintext attack

chosen plaintextchosen plaintext attackchosen plaintexts
A chosen-plaintext attack (CPA) is an attack model for cryptanalysis which presumes that the attacker can obtain the ciphertexts for arbitrary plaintexts.

Chosen-ciphertext attack

chosen ciphertext attackChosen-ciphertextCCA
A chosen-ciphertext attack (CCA) is an attack model for cryptanalysis where the cryptanalyst can gather information by obtaining the decryptions of chosen ciphertexts.

Reverse engineering

reverse engineeredreverse engineerreverse-engineered
Reverse engineering is also being used in cryptanalysis in order to find vulnerabilities in substitution cipher, symmetric-key algorithm or public-key cryptography.

Bletchley Park

Bletchley Park MuseumBletchley Park TrustBletchley
Even though the goal has been the same, the methods and techniques of cryptanalysis have changed drastically through the history of cryptography, adapting to increasing cryptographic complexity, ranging from the pen-and-paper methods of the past, through machines like the British Bombes and Colossus computers at Bletchley Park in World War II, to the mathematically advanced computerized schemes of the present.
Key GC&CS cryptanalysts who moved from London to Bletchley Park included John Tiltman, Dillwyn "Dilly" Knox, Josh Cooper, and Nigel de Grey.

Related-key attack

related key attackrelated-keyrelated key
In cryptography, a related-key attack is any form of cryptanalysis where the attacker can observe the operation of a cipher under several different keys whose values are initially unknown, but where some mathematical relationship connecting the keys is known to the attacker.

History of cryptography

cryptanalysis in World War IIcryptologic historycyphers
Cryptanalysis has coevolved together with cryptography, and the contest can be traced through the history of cryptography—new ciphers being designed to replace old broken designs, and new cryptanalytic techniques invented to crack the improved schemes.
The development of cryptography has been paralleled by the development of cryptanalysis — the "breaking" of codes and ciphers.

Frequency analysis

Frequency analysis (cryptanalysis)frequenciesfrequency analyzed
This treatise contains the first description of the method of frequency analysis.
In cryptanalysis, frequency analysis (also known as counting letters) is the study of the frequency of letters or groups of letters in a ciphertext.

Data Encryption Standard

DESDES encryptionATSC DES
Nonetheless, partial breaks that come close to breaking the original cryptosystem may mean that a full break will follow; the successful attacks on DES, MD5, and SHA-1 were all preceded by attacks on weakened versions.
The intense academic scrutiny the algorithm received over time led to the modern understanding of block ciphers and their cryptanalysis.

Code (cryptography)

codecodescodetext
Although the actual word "cryptanalysis" is relatively recent (it was coined by William Friedman in 1920), methods for breaking codes and ciphers are much older.
Such multiple encryption, or "superencryption" aims to make cryptanalysis more difficult.

Block cipher

block ciphersblockcipher
It also influenced the academic development of cryptanalytic attacks.

Substitution cipher

substitutionmonoalphabetic substitution ciphersubstitution ciphers
For example, in a simple substitution cipher (where each letter is simply replaced with another), the most frequent letter in the ciphertext would be a likely candidate for "E".
Provided the message is of reasonable length (see below), the cryptanalyst can deduce the probable meaning of the most common symbols by analyzing the frequency distribution of the ciphertext.

Enigma machine

EnigmaEnigma codeEnigma cipher machine
In World War II, the Allies benefitted enormously from their joint success cryptanalysis of the German ciphers — including the Enigma machine and the Lorenz cipher — and Japanese ciphers, particularly 'Purple' and JN-25. During World War I, inventors in several countries developed rotor cipher machines such as Arthur Scherbius' Enigma, in an attempt to minimise the repetition that had been exploited to break the Vigenère system.
As used in practice, the Enigma encryption proved vulnerable to cryptanalytic attacks by Germany's adversaries, at first Polish and French intelligence and, later, a massive effort mounted by the United Kingdom at Bletchley Park as part of the Ultra program.

Magic (cryptography)

Magic MAGIC American cryptographers
The war in the Pacific was similarly helped by 'Magic' intelligence.
Magic was an Allied cryptanalysis project during World War II.

Al-Kindi

AlkindusAl-KindīAl Kindi
The first known recorded explanation of cryptanalysis was given by Al-Kindi (c.
Building on the work of Al-Khalil (717–786), Al-Kindi's book entitled Manuscript on Deciphering Cryptographic Messages gave rise to the birth of cryptanalysis, was the earliest known use of statistical inference, and introduced several new methods of breaking ciphers, notably frequency analysis.

Harry Hinsley

F. H. HinsleySir Harry HinsleyF.H. Hinsley
Sir Harry Hinsley, official historian of British Intelligence in World War II, made a similar assessment about Ultra, saying that it shortened the war "by not less than two years and probably by four years"; moreover, he said that in the absence of Ultra, it is uncertain how the war would have ended.
Sir Francis Harry Hinsley OBE (26 November 1918 – 16 February 1998) was an English historian and cryptanalyst.

Statistics

statisticalstatistical analysisstatistician
Frequency analysis relies on a cipher failing to hide these statistics.
This text laid the foundations for statistics and cryptanalysis.

Cipher

cipherscyphercipher machine
Cryptanalysis has coevolved together with cryptography, and the contest can be traced through the history of cryptography—new ciphers being designed to replace old broken designs, and new cryptanalytic techniques invented to crack the improved schemes. Although the actual word "cryptanalysis" is relatively recent (it was coined by William Friedman in 1920), methods for breaking codes and ciphers are much older.
However, codes have a variety of drawbacks, including susceptibility to cryptanalysis and the difficulty of managing a cumbersome codebook.

Colossus computer

ColossusColossus (computer)Colossus computers
Even though the goal has been the same, the methods and techniques of cryptanalysis have changed drastically through the history of cryptography, adapting to increasing cryptographic complexity, ranging from the pen-and-paper methods of the past, through machines like the British Bombes and Colossus computers at Bletchley Park in World War II, to the mathematically advanced computerized schemes of the present.
Colossus was a set of computers developed by British codebreakers in the years 1943–1945 to help in the cryptanalysis of the Lorenz cipher.