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The cipher now known as the Vigenère cipher, however, is based on that originally described by Giovan Battista Bellaso in his 1553 book La cifra del Sig. Giovan Battista Bellaso. [8] He built upon the tabula recta of Trithemius but added a repeating "countersign" (a key) to switch cipher alphabets every letter.
To decrypt, the process is reversed. Unlike the otherwise very similar Vigenère cipher, the Beaufort cipher is a reciprocal cipher, that is, decryption and encryption algorithms are the same. This obviously reduces errors in handling the table which makes it useful for encrypting larger volumes of messages by hand, for example in the manual ...
For this encipherment Alberti used a decoder device, his cipher disk, which implemented a polyalphabetic substitution with mixed alphabets. Johannes Trithemius—in his book Polygraphiae libri sex (Six books of polygraphia), which was published in 1518 after his death—invented a progressive key polyalphabetic cipher called the Trithemius ...
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 ...
Kasiski actually used "superimposition" to solve the Vigenère cipher. He started by finding the key length, as above. Then he took multiple copies of the message and laid them one-above-another, each one shifted left by the length of the key. Kasiski then observed that each column was made up of letters encrypted with a single alphabet. His ...
In classical cryptography, the running key cipher is a type of polyalphabetic substitution cipher in which a text, typically from a book, is used to provide a very long keystream. The earliest description of such a cipher was given in 1892 by French mathematician Arthur Joseph Hermann (better known for founding Éditions Hermann ).
Code books contain two lists – one of code groups and one of plaintext letters, words, and phrases. Someone encoding a message looks up the words in the plaintext list and substitutes the corresponding code group. Obviously it is important for that person's sanity that the plaintext be in some sort of order so words can be looked up easily.
Polygraphic substitution is a cipher in which a uniform substitution is performed on blocks of letters. When the length of the block is specifically known, more precise terms are used: for instance, a cipher in which pairs of letters are substituted is bigraphic.