* Alberti was an accomplished cryptographer by the standard of his day, and invented the first polyalphabetic cipher which is now known as the Alberti cipher and machine-assisted encryption using his Cipher Disk.

These produced a polyalphabetic substitution cipher, and were widely thought to be unbreakable in the 1920s, when a variant of the commercial Model D was first used by the German military.

It produced a polyalphabetic substitution cipher, but unlike the Enigma machines, it was not a rotor machine, being built around electrical stepping switches.

* The polyalphabetic cipher is invented by Leone Battista Alberti ( approximate date ).

A monoalphabetic cipher uses fixed substitution over the entire message, whereas a polyalphabetic cipher uses a number of substitutions at different positions in the message, where a unit from the plaintext is mapped to one of several possibilities in the ciphertext and vice versa.

The replacement remains the same throughout the message, so the cipher is classed as a type of monoalphabetic substitution, as opposed to polyalphabetic substitution.

The first well documented description of a polyalphabetic cipher was formulated by Leon Battista Alberti around 1467 and used a metal cipher disc to switch between cipher alphabets.

A polyalphabetic cipher is any cipher based on 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 still fundamentally a polyalphabetic substitution cipher.

The Alberti cipher by Leon Battista Alberti around 1467 was believed to be the first polyalphabetic cipher.

For this encipherment Alberti used a decoder device, his cipher disk, which implemented a polyalphabetic substitution with mixed alphabets.

Although Alberti is usually considered the father of polyalphabetic cipher, it has been claimed that polyalphabetic ciphers may have been developed by the Arab cryptologist Al Kindi 600 years before Alberti. Johannes Trithemius, in a book published after his death, invented a progressive key polyalphabetic cipher called the Trithemius cipher.

Even Alberti's implementation of his polyalphabetic cipher was rather easy to break ( the capitalized letter is a major clue to the cryptanalyst ).

It was not until the mid-19th century ( in Babbage's secret work during the Crimean War and Friedrich Kasiski's generally equivalent public disclosure some years later ), that cryptanalysis of well-implemented polyalphabetic ciphers got anywhere at all.

Trithemius used the tabula recta to define a polyalphabetic cipher which was equivalent to Leon Battista Alberti's cipher disk except that the alphabets are not mixed.

In the mid-15th century, a new technique was invented by Alberti, now known generally as polyalphabetic ciphers, which recognised the virtue of using more than a single substitution alphabet ; he also invented a simple technique for " creating " a multitude of substitution patterns for use in a message.

Not until the 1840s ( Babbage ) was any technique known which could reliably break any of the polyalphabetic ciphers.

Enigma, and the rotor machines generally, were just what was needed since they were seriously polyalphabetic, using a different substitution alphabet for each letter of plaintext, and automatic, requiring no extraordinary abilities from their users.

The most effective way to defeat frequency analysis attacks was the polyalphabetic substitution cipher, invented by Alberti about 1465.

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 kept it secret ).

The polyalphabetic cipher was most clearly explained by Leon Battista Alberti around the year 1467, for which he was called the " father of Western cryptology ".

Gilbert Sandford Vernam ( 3 April 1890 – 7 February 1960 ) was an AT & T Bell Labs engineer who, in 1917, invented an additive polyalphabetic stream cipher and later co-invented an automated one-time pad cipher.

It generated a polyalphabetic substitution cipher, with a period before repetition of the substitution alphabet that was much longer than any message, or set of messages, sent with the same key.

During World War I, inventors in several countries realized that a purely random key sequence, containing no repetitive pattern, would, in principle, make a polyalphabetic substitution cipher unbreakable.

Simple ciphers were replaced by polyalphabetic substitution ciphers which changed the substitution alphabet for every letter.

With even a small amount of known or estimated plaintext, simple polyalphabetic substitution ciphers and letter transposition ciphers designed for pen and paper encryption are easy to crack.

Since Dee is well-known to have been a spy for Elizabeth I's court, there are many modern interpretations of his Angelic manuscripts as cryptographic documents-most likely polyalphabetic ciphers-designed to disguise political messages ( see for instance, Langford This aspect of the manuscripts is not of major concern to Enochian magicians, but there is no doubt that Dee's knowledge of mathematics and sophisticated cipher systems contributed extensively to his magical system.

Rather than the complex polyalphabetic Alberti cipher method, the decoders for children invariably use simple Caesar cipher substitutions.

* Friedrich Kasiski, Die Geheimschriften und die Dechiffrierkunst (" Secret writing and the Art of Deciphering "), pub 1863, contained the first public description of a technique for cryptanalyzing polyalphabetic cyphers.

Al-Kindi wrote a book on cryptography entitled Risalah fi Istikhraj al-Mu ' amma ( Manuscript for the Deciphering Cryptographic Messages ), in which he described the first cryptanalysis techniques, including some for polyalphabetic ciphers, cipher classification, Arabic phonetics and syntax, and, most importantly, gave the first descriptions on frequency analysis.

For instance, in Europe during and after the Renaissance, citizens of the various Italian states — the Papal States and the Roman Catholic Church included — were responsible for rapid proliferation of cryptographic techniques, few of which reflect understanding ( or even knowledge ) of Alberti's polyalphabetic advance.

For a repeating-key polyalphabetic cipher arranged into a matrix, the coincidence rate within each column will usually be highest when the width of the matrix is a multiple of the key length, and this fact can be used to determine the key length, which is the first step in cracking the system.

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.

It is also possible to have a polyalphabetic substitution cipher, where multiple cipher alphabets are used.

The Kasiski examination allows a cryptanalyst to deduce the length of the keyword used in the polyalphabetic substitution cipher.

These digits are then used to navigate through a number of printed tables to create a polyalphabetic cipher.

In rotor machines, several rotor disks provided polyalphabetic substitution, while plug boards provided another substitution.

While Carroll calls this cipher " unbreakable ", Kasiski had published a volume describing how to break such ciphers from five years earlier, and Charles Babbage had secretly found ways to break polyalphabetic ciphers during the Crimean War.

Cryptography historian David Kahn titles him the " Father of Western Cryptography ", pointing to three significant advances in the field which can be attributed to Alberti: " the earliest Western exposition of cryptanalysis, the invention of polyalphabetic substitution, and the invention of enciphered code " ().

During the early twentieth century, electro-mechanical machines were invented to do encryption and decryption using transposition, polyalphabetic substitution, and a kind of " additive " substitution.

It is a simple form of polyalphabetic substitution.