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Hill's cipher machine, from figure 4 of the patent. In classical cryptography, the Hill cipher is a polygraphic substitution cipher based on linear algebra.Invented by Lester S. Hill in 1929, it was the first polygraphic cipher in which it was practical (though barely) to operate on more than three symbols at once.
In cryptography, a substitution cipher is a method of encrypting in which units of plaintext are replaced with the ciphertext, in a defined manner, with the help of a key; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth.
Lester S. Hill (1891–1961) was an American mathematician and educator who was interested in applications of mathematics to communications.He received a bachelor's degree (1911) and a master's degree (1913) from Columbia College and a Ph.D. from Yale University (1926).
In 1929, Lester S. Hill developed the Hill cipher, which uses matrix algebra to encrypt blocks of any desired length. However, encryption is very difficult to perform by hand for any sufficiently large block size, although it has been implemented by machine or computer. This is therefore on the frontier between classical and modern cryptography.
The affine cipher is a type of monoalphabetic substitution cipher, where each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter. The formula used means that each letter encrypts to one other letter, and back again, meaning the cipher is essentially a ...
CMEA – cipher used in US cellphones, found to have weaknesses. CS-Cipher – 64-bit block; Data Encryption Standard (DES) – 64-bit block; FIPS 46-3, 1976; DEAL – an AES candidate derived from DES; DES-X – a variant of DES to increase the key size. FEAL; GDES – a DES variant designed to speed up encryption; Grand Cru – 128-bit block
Another example of a polyalphabetic substitution cipher that is much more difficult to decode is the Vigenère square, an innovative encoding method. With the square, there are 26 different cipher alphabets that are used to encrypt text. Each cipher alphabet is just another rightward Caesar shift of the original alphabet.
In cryptography, unicity distance is the length of an original ciphertext needed to break the cipher by reducing the number of possible spurious keys to zero in a brute force attack. That is, after trying every possible key , there should be just one decipherment that makes sense, i.e. expected amount of ciphertext needed to determine the key ...