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A disk cipher device of the Jefferson type from the 2nd quarter of the 19th century in the National Cryptologic Museum. The Jefferson disk, also called the Bazeries cylinder or wheel cypher, [1] was a cipher system commonly attributed to Thomas Jefferson that uses a set of wheels or disks, each with letters of the alphabet arranged around their edge in an order, which is different for each ...
It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. [1] The method is named after Julius Caesar, who used it in his private correspondence.
Each letter is treated as a digit in base 26: A = 0, B =1, and so on. (In a variation, 3 extra symbols are added to make the basis prime.) A block of n letters is then considered as a vector of n dimensions, and multiplied by a n x n matrix, modulo 26.
A book cipher is a cipher in which each word or letter in the plaintext of a message is replaced by some code that locates it in another text, the key. A simple version of such a cipher would use a specific book as the key, and would replace each word of the plaintext by a number that gives the position where that word occurs in that book.
Codes generally substitute different length strings of characters in the output, while ciphers generally substitute the same number of characters as are input. A code maps one meaning with another. Words and phrases can be coded as letters or numbers. Codes typically have direct meaning from input to key. Codes primarily function to save time.
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These approaches combine a pseudo-random number generator (often in the form of a block or stream cipher) with an external source of randomness (e.g., mouse movements, delay between keyboard presses etc.). /dev/random – Unix-like systems; CryptGenRandom – Microsoft Windows; Fortuna
The Alberti Cipher disk. The Alberti Cipher, created in 1467 by Italian architect Leon Battista Alberti, was one of the first polyalphabetic ciphers. [1] In the opening pages of his treatise De componendis cifris [] he explained how his conversation with the papal secretary Leonardo Dati about a recently developed movable type printing press led to the development of his cipher wheel.