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The Vigenère cipher is simple enough to be a field cipher if it is used in conjunction with cipher disks. [13] The Confederate States of America, for example, used a brass cipher disk to implement the Vigenère cipher during the American Civil War. The Confederacy's messages were far from secret, and the Union regularly cracked its messages.
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.
The Vigenère cipher is probably the most famous example of a polyalphabetic substitution cipher. [21] The famous cipher machines of World War II encipher in a polyalphabetic system. Their strength came from the enormous number of well-mixed alphabets that they used and the fairly random way of switching between them.
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]
An autokey cipher (also known as the autoclave cipher) is a cipher that incorporates the message (the plaintext) into the key. The key is generated from the message in some automated fashion, sometimes by selecting certain letters from the text or, more commonly, by adding a short primer key to the front of the message.
In 1553 he published his first and most important booklet: La Cifra del Sig. Giovan Battista Bel[l]aso, dedicated to Girolamo Ruscelli. For the implementation of this cipher a table is formed by sliding the lower half of an ordinary alphabet for an apparently random number of places with respect to the upper half.
Some substitution ciphers involve using numbers instead of letters. An example of this is the Great Cipher, where numbers were used to represent syllables. There is also another number substitution cipher [which?] that involves having four different number pair options for a letter based on a keyword.
The number of cipher alphabets used in a polyalphabetic cipher may be estimated by dividing the expected bulge of the delta I.C. for a single alphabet by the observed bulge for the message, although in many cases (such as when a repeating key was used) better techniques are available.