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Despite the Vigenère cipher's apparent strength, it never became widely used throughout Europe. The Gronsfeld cipher is a variant attributed by Gaspar Schott to Count Gronsfeld (Josse Maximilaan van Gronsveld né van Bronckhorst) but was actually used much earlier by an ambassador of Duke of Mantua in 1560s-1570s. It is identical to the ...
In cryptanalysis and computer security, a dictionary attack is an attack using a restricted subset of a keyspace to defeat a cipher or authentication mechanism by trying to determine its decryption key or passphrase, sometimes trying thousands or millions of likely possibilities [1] often obtained from lists of past security breaches.
In polyalphabetic substitution ciphers where the substitution alphabets are chosen by the use of a keyword, the Kasiski examination allows a cryptanalyst to deduce the length of the keyword. Once the length of the keyword is discovered, the cryptanalyst lines up the ciphertext in n columns, where n is the length of the keyword.
Classical ciphers are typically vulnerable to known-plaintext attack. For example, a Caesar cipher can be solved using a single letter of corresponding plaintext and ciphertext to decrypt entirely. A general monoalphabetic substitution cipher needs several character pairs and some guessing if there are fewer than 26 distinct pairs.
The next development was the paper pad system. Diplomats had long used codes and ciphers for confidentiality and to minimize telegraph costs. For the codes, words and phrases were converted to groups of numbers (typically 4 or 5 digits) using a dictionary-like codebook.
In 1863, Kasiski published a 95-page book on cryptography, Die Geheimschriften und die Dechiffrir-Kunst (German, "Secret writing and the Art of Deciphering"). This was the first published account of a procedure for attacking polyalphabetic substitution ciphers, especially the Vigenère cipher (although it is possible Charles Babbage was already aware of a similar method but had not published it).
Weak ciphers do not sufficiently mask the distribution, and this might be exploited by a cryptanalyst to read the message. In cryptanalysis, frequency analysis (also known as counting letters) is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers.
More common methods of password cracking, such as dictionary attacks, pattern checking, and variations of common words, aim to optimize the number of guesses and are usually attempted before brute-force attacks. Higher password bit strength exponentially increases the number of candidate passwords that must be checked, on average, to recover ...