Cipher in the context of Stream cipher

The Voynich manuscript is an illustrated codex, hand-written in an unknown script referred to as Voynichese. The vellum on which it is written has been carbon-dated to the early 15th century (1404–1438). Stylistic analysis has indicated the manuscript may have been composed in Italy during the Italian Renaissance. The origins, authorship, and purpose of the manuscript are still debated, but currently scholars lack the translation(s) and context needed to either properly entertain or eliminate any of the possibilities. Hypotheses range from a script for a natural language or constructed language, an unreadable code, cypher, or other form of cryptography, or perhaps a hoax, reference work (i.e. folkloric index or compendium), glossolalia or work of fiction (e.g. science fantasy or mythopoeia, metafiction, speculative fiction).

The first confirmed owner was Georg Baresch, a 17th-century alchemist from Prague. The manuscript is named after Wilfrid Voynich, a Polish book dealer who purchased it in 1912. The manuscript consists of around 240 pages, but there is evidence that some of the pages are missing. The text is written from left to right, and some pages are foldable sheets of varying sizes. Most of the pages have fantastical illustrations and diagrams, some crudely coloured, with sections of the manuscript showing people, unidentified plants and astrological symbols. Since 1969, it has been held in Yale University's Beinecke Rare Book and Manuscript Library. In 2020, Yale University published the manuscript online in its entirety in their digital library.

In numerology, gematria (/ɡəˈmeɪtriə/; Hebrew: גמטריא or גימטריה, gimatriyyā, plural גמטראות or גימטריות, gimatriyyot, borrowed via Aramaic from Koine Greek: γραμμάτια) is the practice of assigning a numerical value to a name, word, or phrase by reading it as a number, or sometimes by using an alphanumeric cipher. The letters of the alphabets involved have standard numerical values, but a word can yield several values if a cipher is used.

According to Aristotle (384–322 BCE), isopsephy, based on the Greek numerals developed in the city of Miletus in Anatolia, was part of the Pythagoreanism, which originated in the 6th century BCE. The first evidence of use of Hebrew letters as numbers dates to 78 BCE; gematria is still used in Jewish culture. Similar systems have been used in other languages and cultures, derived from or inspired by either Greek isopsephy or Hebrew gematria, and include Arabic abjad numerals and English gematria.

In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher to decrypt it. This process prevents the loss of sensitive information via hacking. Decryption, the inverse of encryption, is the process of turning ciphertext into readable plaintext. Ciphertext is not to be confused with codetext, because the latter is a result of a code, not a cipher.

Mirror writing is formed by writing in the direction that is the reverse of the natural way for a given language, such that the result is the mirror image of normal writing: it appears normal when reflected in a mirror. It is sometimes used as an extremely primitive form of cipher. A common modern usage of mirror writing can be found on the front of ambulances, where the word "AMBULANCE" is often written in very large mirrored text, so that drivers see the word the right way around in their rear-view mirror. It is also on fire engines and police cars too.

Some people are able to produce handwritten mirrored text. Notably, Leonardo da Vinci wrote most of his personal notes in this way.Mirror writing calligraphy was popular in the Ottoman Empire, where it often carried mystical associations.

Alan Mathison Turing (/ˈtjʊərɪŋ/; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist. He was highly influential in the development of theoretical computer science, providing a formalisation of the concepts of algorithm and computation with the Turing machine, which can be considered a model of a general-purpose computer. Turing is widely considered to be the father of theoretical computer science.

Born in London, Turing was raised in southern England. He graduated from King's College, Cambridge, and in 1938, earned a doctorate degree from Princeton University. During World War II, Turing worked for the Government Code and Cypher School at Bletchley Park, Britain's codebreaking centre that produced Ultra intelligence. He led Hut 8, the section responsible for German naval cryptanalysis. Turing devised techniques for speeding the breaking of German ciphers, including improvements to the pre-war Polish bomba method, an electromechanical machine that could find settings for the Enigma machine. He played a crucial role in cracking intercepted messages that enabled the Allies to defeat the Axis powers in the Battle of the Atlantic and other engagements.

The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the German military. The Enigma machine was considered so secure that it was used to encipher the most top-secret messages.

The Enigma has an electromechanical rotor mechanism that scrambles the 26 letters of the alphabet. In typical use, one person enters text on the Enigma's keyboard and another person writes down which of the 26 lights above the keyboard illuminated at each key press. If plaintext is entered, the illuminated letters are the ciphertext. Entering ciphertext transforms it back into readable plaintext. The rotor mechanism changes the electrical connections between the keys and the lights with each keypress. In essence, the rotor's motion means every letter is encrypted with a different cryptographic key, making it highly resistant to conventional cryptographic attacks based on patterns the keys leave in the resulting cyphertext.

The Austrian resistance was launched in response to the rise of the fascists across Europe and, more specifically, to the Anschluss in 1938 and resulting occupation of Austria by Germany.

An estimated 100,000 people were reported to have participated in this resistance with thousands subsequently imprisoned or executed for their anti-Nazi activities. The main cipher of the Austrian resistance was O5, in which "O" indicates the first letter of the abbreviation of Österreich (OE), with the "5" indicating the fifth letter of the German alphabet (E). This sign may be seen at the Stephansdom in Vienna.

Cryptanalysis of the Enigma ciphering system enabled the western Allies in World War II to read substantial amounts of Morse-coded radio communications of the Axis powers that had been enciphered using Enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio and teleprinter transmissions, was given the codename Ultra.

The Enigma machines were a family of portable cipher machines with rotor scramblers. Good operating procedures, properly enforced, would have made the plugboard Enigma machine unbreakable to the Allies at that time.

Trigrams are a special case of the n-gram, where n is 3. They are often used in natural language processing for performing statistical analysis of texts and in cryptography for control and use of ciphers and codes. See results of analysis of "Letter Frequencies in the English Language".

The pigpen cipher (alternatively referred to as the masonic cipher, Freemason's cipher, Rosicrucian cipher, Napoleon cipher, and tic-tac-toe cipher) is a geometric simple substitution cipher, which exchanges letters for symbols which are fragments of a grid. The example key shows one way the letters can be assigned to the grid.

In cryptography, a classical cipher is a type of cipher that was used historically but for the most part, has fallen into disuse. In contrast to modern cryptographic algorithms, most classical ciphers can be practically computed and solved by hand. However, they are also usually very simple to break with modern technology. The term includes the simple systems used since Greek and Roman times, the elaborate Renaissance ciphers, World War II cryptography such as the Enigma machine and beyond.

In contrast, modern strong cryptography relies on new algorithms and computers developed since the 1970s.

A pseudoword is a unit of speech or text that appears to be an actual word in a certain language, while in fact it has no meaning. It is a specific type of nonce word, or even more narrowly a nonsense word, composed of a combination of phonemes which nevertheless conform to the language's phonotactic rules. It is thus a kind of vocable: utterable but meaningless.

Such words lacking a meaning in a certain language or absent in any text corpus or dictionary can be the result of (the interpretation of) a truly random signal, but there will often be an underlying deterministic source, as is the case for examples like jabberwocky and galumph (both coined in a nonsense poem by Lewis Carroll), dord (a ghost word published due to a mistake), ciphers, and typos.

The Alphabetum Kaldeorum ("alphabet of the Chaldeans") is one of the best known ciphers of the Middle Ages. Its name refers to Chaldea, whose inhabitants during the medieval era were reputed to have mysterious and magical knowledge.

It can be found in a complete version, together with other non-Latin alphabets, in a manuscript from the year 1428, now in the library at the University of Munich (Cod. 4º 810, fol. 41v). However, its origins lie clearly in an earlier time, as some examples of its practical use demonstrate.

Gilbert Sandford Vernam (April 3, 1890 – February 7, 1960) was a Worcester Polytechnic Institute 1914 graduate and AT&T Bell Labs engineer who, in 1917, invented an additive polyalphabetic stream cipher and later co-invented an automated one-time pad cipher. Vernam proposed a teleprinter cipher in which a previously prepared key, kept on paper tape, is combined character by character with the plaintext message to produce the ciphertext. To decipher the ciphertext, the same key would be again combined character by character, producing the plaintext. Vernam later worked for the Postal Telegraph Company, and became an employee of Western Union when that company acquired Postal in 1943. His later work was largely with automatic switching systems for telegraph networks.

In cryptography, a cryptosystem is a suite of cryptographic algorithms needed to implement a particular security service, such as confidentiality (encryption).

Typically, a cryptosystem consists of three algorithms: one for key generation, one for encryption, and one for decryption. The term cipher (sometimes cypher) is often used to refer to a pair of algorithms, one for encryption and one for decryption. Therefore, the term cryptosystem is most often used when the key generation algorithm is important. For this reason, the term cryptosystem is commonly used to refer to public key techniques; however both "cipher" and "cryptosystem" are used for symmetric key techniques.

Cryptographic primitives are well-established, low-level cryptographic algorithms that are frequently used to build cryptographic protocols for computer security systems. These routines include, but are not limited to, one-way hash functions and encryption functions.