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If it is assumed that the repeated segments represent the same plaintext segments, that implies that the key is 16, 8, 4, 2, or 1 characters long. (All factors of the distance are possible key lengths; a key of length one is just a simple Caesar cipher, and its cryptanalysis is much easier.) Since key lengths 2 and 1 are unrealistically short ...
In cryptanalysis, Kasiski examination (also known as Kasiski's test or Kasiski's method) is a method of attacking polyalphabetic substitution ciphers, such as the Vigenère cipher. [1] [2] It was first published by Friedrich Kasiski in 1863, [3] but seems to have been independently discovered by Charles Babbage as early as 1846. [4] [5]
600-500 – Hebrew scholars make use of simple monoalphabetic substitution ciphers (such as the Atbash cipher) c. 400 – Spartan use of scytale (alleged) c. 400 – Herodotus reports use of steganography in reports to Greece from Persia (tattoo on shaved head) 100-1 A.D.- Notable Roman ciphers such as the Caesar cipher.
A polyalphabetic cipher is a substitution, using multiple substitution alphabets. The Vigenère cipher is probably the best-known example of a polyalphabetic cipher, though it is a simplified special case. The Enigma machine is more complex but is still fundamentally a polyalphabetic substitution cipher.
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).
where U is the unicity distance, H(k) is the entropy of the key space (e.g. 128 for 2 128 equiprobable keys, rather less if the key is a memorized pass-phrase). D is defined as the plaintext redundancy in bits per character. Now an alphabet of 32 characters can carry 5 bits of information per character (as 32 = 2 5).
It is very similar to the Vigenère cipher, making many scholars call Bellaso its inventor, although unlike the modern Vigenère cipher Bellaso didn't use 26 different "shifts" (different Caesar's ciphers) for every letter, instead opting for 13 shifts for pairs of letters. The system is still periodic although the use of one or more long ...
At the end of every season 1 episode of the cartoon series Gravity Falls, during the credit roll, there is one of three simple substitution ciphers: A -3 Caesar cipher (hinted by "3 letters back" at the end of the opening sequence), an Atbash cipher, or a letter-to-number simple substitution cipher. The season 1 finale encodes a message with ...