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Polygraphic Substitution
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. As a concept, polygraphic substitution contrasts with monoalphabetic (or simple) substitutions in which individual letters are uniformly substituted, or polyalphabetic substitutions in which individual letters are substituted in different ways depending on their position in the text. In theory, there is some overlap in these definitions; one could conceivably consider a Vigenère cipher with an eight-letter key to be an octographic substitution. In practice, this is not a useful observation since it is far more fruitful to consider it to be a polyalphabetic substitution cipher. Specific ciphers In 1563, Giambattista della Porta devised the first biographic substitution. However, it was nothing more than a matrix of sym ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyalphabetic Substitution
A polyalphabetic cipher 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 is still fundamentally a polyalphabetic substitution cipher. History The work of Al-Qalqashandi (1355–1418), based on the earlier work of Ibn al-Durayhim (1312–1359), contained the first published discussion of the substitution and transposition of ciphers, as well as the first description of a polyalphabetic cipher, in which each plaintext letter is assigned more than one substitute. However, it has been claimed that polyalphabetic ciphers may have been developed by the Arab cryptologist Al Kindi (801–873) centuries earlier. The Alberti cipher by Leon Battista Alberti around 1467 was an early polyalphabetic cipher. Alberti used a mixed alphabet to encrypt a message, but whenever he wanted to, he would switch to a different alphabet, ind ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vigenère Cipher
The Vigenère cipher () is a method of encryption, encrypting alphabetic text by using a series of interwoven Caesar ciphers, based on the letters of a keyword. It employs a form of polyalphabetic cipher, polyalphabetic substitution. First described by Giovan Battista Bellaso in 1553, the cipher is easy to understand and implement, but it resisted all attempts to break it until 1863, three centuries later. This earned it the description le chiffrage indéchiffrable (French language, French for 'the indecipherable cipher'). Many people have tried to implement encryption schemes that are essentially Vigenère ciphers. In 1863, Friedrich Kasiski was the first to publish a general method of deciphering Vigenère ciphers. In the 19th century, the scheme was misattributed to Blaise de Vigenère (1523–1596) and so acquired its present name. History The very first well-documented description of a polyalphabetic cipher was by Leon Battista Alberti around 1467 and used a metal cipher ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Giambattista Della Porta
Giambattista della Porta (; 1535 – 4 February 1615), also known as Giovanni Battista Della Porta, was an Italian scholar, polymath and playwright who lived in Naples at the time of the Renaissance, Scientific Revolution and Reformation. Giambattista della Porta spent the majority of his life on scientific endeavors. He benefited from an informal education of tutors and visits from renowned scholars. His most famous work, first published in 1558, is entitled ''Magia Naturalis (Natural Magic).'' In this book he covered a variety of the subjects he had investigated, including occult philosophy, astrology, alchemy, mathematics, meteorology, and natural philosophy. He was also referred to as "professor of secrets". Childhood Giambattista della Porta was born at Vico Equense, near Naples, to the nobleman Nardo Antonio della Porta. He was the third of four sons and the second to survive childhood, having an older brother Gian Vincenzo and a younger brother Gian Ferrante.Giambattist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charles Wheatstone
Sir Charles Wheatstone FRS FRSE DCL LLD (6 February 1802 – 19 October 1875), was an English scientist and inventor of many scientific breakthroughs of the Victorian era, including the English concertina, the stereoscope (a device for displaying three-dimensional images), and the Playfair cipher (an encryption technique). However, Wheatstone is best known for his contributions in the development of the Wheatstone bridge, originally invented by Samuel Hunter Christie, which is used to measure an unknown electrical resistance, and as a major figure in the development of telegraphy. Life Charles Wheatstone was born in Barnwood, Gloucestershire. His father, W. Wheatstone, was a music-seller in the town, who moved to 128 Pall Mall, London, four years later, becoming a teacher of the flute. Charles, the second son, went to a village school, near Gloucester, and afterwards to several institutions in London. One of them was in Kennington, and kept by a Mrs. Castlemaine, who ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Playfair Cipher
The Playfair cipher or Playfair square or Wheatstone–Playfair cipher is a manual symmetric encryption technique and was the first literal digram substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair for promoting its use. The technique encrypts pairs of letters (''bigrams'' or ''digrams''), instead of single letters as in the simple substitution cipher and rather more complex Vigenère cipher systems then in use. The Playfair is thus significantly harder to break since the frequency analysis used for simple substitution ciphers does not work with it. The frequency analysis of bigrams is possible, but considerably more difficult. With 600 possible bigrams rather than the 26 possible monograms (single symbols, usually letters in this context), a considerably larger cipher text is required in order to be useful. History The Playfair cipher was the first cipher to encrypt pairs of letters in cryptologic history. Wheat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Four-square Cipher
The four-square cipher is a manual symmetric encryption technique. It was invented by the French cryptographer Felix Delastelle. The technique encrypts pairs of letters (''digraphs''), and thus falls into a category of ciphers known as polygraphic substitution ciphers. This adds significant strength to the encryption when compared with monographic substitution ciphers which operate on single characters. The use of digraphs makes the four-square technique less susceptible to frequency analysis attacks, as the analysis must be done on 676 possible digraphs rather than just 26 for monographic substitution. The frequency analysis of digraphs is possible, but considerably more difficult - and it generally requires a much larger ciphertext in order to be useful. Using four-square The four-square cipher uses four 5 by 5 (5x5) matrices arranged in a square. Each of the 5 by 5 matrices contains the letters of the alphabet (usually omitting "Q" or putting both "I" and "J" in the same ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Two-square Cipher
The Two-square cipher, also called double Playfair, is a manual symmetric encryption technique. It was developed to ease the cumbersome nature of the large encryption/decryption matrix used in the four-square cipher while still being slightly stronger than the single-square Playfair cipher. The technique encrypts pairs of letters (''digraphs''), and thus falls into a category of ciphers known as polygraphic substitution ciphers. This adds significant strength to the encryption when compared with monographic substitution ciphers, which operate on single characters. The use of digraphs makes the two-square technique less susceptible to frequency analysis attacks, as the analysis must be done on 676 possible digraphs rather than just 26 for monographic substitution. The frequency analysis of digraphs is possible, but considerably more difficult, and it generally requires a much larger ciphertext in order to be useful. History Félix Delastelle described the cipher in his 1901 book ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lester S
Lester is an ancient Anglo-Saxon surname and given name. Notable people and characters with the name include: People Given name * Lester Bangs (1948–1982), American music critic * Lester W. Bentley (1908–1972), American artist from Wisconsin * Lester Bird (1938–2021), second prime minister of Antigua and Barbuda (1994–2004) * Lester Cotton (born 1996), American football player * Lester del Rey (1915–1993), American science fiction author and editor * Lester Flatt (1914–1979), American bluegrass musician * Lester Gillis (1908–1934), better known as Baby Face Nelson, American gangster * Lester Holt (born 1959), American television journalist * Lester Charles King (1907–1989), English geomorphologist * Lester Lanin (1907–2004), American jazz and pop music bandleader * Lester Lockett (1912–2005), American Negro League baseball player * Lester Maddox (1915–2003), governor and lieutenant governor of the U.S. state of Georgia * Lester Patrick (1883–1960), Can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hill Cipher
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. The following discussion assumes an elementary knowledge of matrices. Encryption Each letter is represented by a number modulo 26. Though this is not an essential feature of the cipher, this simple scheme is often used: To encrypt a message, each block of ''n'' letters (considered as an ''n''-component vector) is multiplied by an invertible ''n'' × ''n'' matrix, against modulus 26. To decrypt the message, each block is multiplied by the inverse of the matrix used for encryption. The matrix used for encryption is the cipher key, and it should be chosen randomly from the set of invertible ''n'' × ''n'' matrices ( modulo 26). The cipher can, of course, be adapted to an alphabet with any number of letters; ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Topics In Cryptography
The following outline is provided as an overview of and topical guide to cryptography: Cryptography (or cryptology) – practice and study of hiding information. Modern cryptography intersects the disciplines of mathematics, computer science, and engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce. Essence of cryptography * Cryptographer * Encryption/decryption * Cryptographic key * Cipher * Ciphertext * Plaintext * Code * Tabula recta * Alice and Bob Uses of cryptographic techniques * Commitment schemes * Secure multiparty computation * Electronic voting * Authentication * Digital signatures * Crypto systems * Dining cryptographers problem * Anonymous remailer * Pseudonymity * Onion routing * Digital currency * Secret sharing * Indistinguishability obfuscation Branches of cryptography * Multivariate cryptography * Post-quantum cryptography * Quantum cryptography * Steganography * Visual cryptography History ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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