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Autokey Cipher
An autokey cipher (also known as the autoclave cipher) is a cipher that incorporates the message (the plaintext) into the key. The key is generated from the message in some automated fashion, sometimes by selecting certain letters from the text or, more commonly, by adding a short ''primer key'' to the front of the message. There are two forms of autokey cipher: ''key-autokey'' and ''text-autokey'' ciphers. A key-autokey cipher uses previous members of the keystream to determine the next element in the keystream. A text-autokey uses the previous message text to determine the next element in the keystream. History This cipher was invented in 1586 by Blaise de Vigenère with a reciprocal table of ten alphabets. Vigenère's version used an agreed-upon letter of the alphabet as a primer, making the key by writing down that letter and then the rest of the message. More popular autokeys use a tabula recta, a square with 26 copies of the alphabet, the first line starting with 'A', th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cipher
In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode is to convert information into cipher or code. In common parlance, "cipher" is synonymous with "code (cryptography), code", as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially classical cryptography. 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. Ciphers are algorithmic. The given input must follow the cipher's process to be solved. Ciphers are commonly used to encrypt written info ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plaintext
In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted. Overview With the advent of computing, the term ''plaintext'' expanded beyond human-readable documents to mean any data, including binary files, in a form that can be viewed or used without requiring a key or other decryption device. Information—a message, document, file, etc.—if to be communicated or stored in an unencrypted form is referred to as plaintext. Plaintext is used as input to an encryption algorithm; the output is usually termed ciphertext, particularly when the algorithm is a cipher. Codetext is less often used, and almost always only when the algorithm involved is actually a code. Some systems use multiple layers of encryption, with the output of one encryption algorithm becoming "plaintext" input for the next. Secure handling Insecure handling of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Key (cryptography)
A key in cryptography is a piece of information, usually a string of numbers or letters that are stored in a file, which, when processed through a cryptographic algorithm, can encode or decode cryptographic data. Based on the used method, the key can be different sizes and varieties, but in all cases, the strength of the encryption relies on the security of the key being maintained. A key's security strength is dependent on its algorithm, the size of the key, the generation of the key, and the process of key exchange. Scope The key is what is used to encrypt data from plaintext to ciphertext. There are different methods for utilizing keys and encryption. Symmetric cryptography Symmetric cryptography refers to the practice of the same key being used for both encryption and decryption. Asymmetric cryptography Asymmetric cryptography has separate keys for encrypting and decrypting. These keys are known as the public and private keys, respectively. Purpose Since the key ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keystream
In cryptography, a keystream is a stream of random or pseudorandom characters that are combined with a plaintext message to produce an encrypted message (the ciphertext). The "characters" in the keystream can be bit The bit is the most basic unit of information in computing and digital communication. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as ...s, bytes, numbers or actual characters like A-Z depending on the usage case. Usually each character in the keystream is either added, subtracted or bitwise XOR, XORed with a character in the plaintext to produce the ciphertext, using modular arithmetic. Keystreams are used in the one-time pad cipher and in most stream ciphers. Block ciphers can also be used to produce keystreams. For instance, CTR mode is a Block cipher modes of operation, block mode that makes a block cipher produce a keystream and thus turns the block ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blaise De Vigenère
Blaise de Vigenère (5 April 1523 – 19 February 1596) () was a French diplomat, cryptographer, translator and alchemist. Biography Vigenère was born into a respectable family in the village of Saint-Pourçain in Bourbonnais. When he was 12, his father, Jehan (modern spelling Jean) de Vigenère, arranged for him to have a classical education in Paris. Registered at the university at 14, he quit after three years without a known degree.Sarazin 1997, p. 18. From 1539 to around 1545, he worked under Gilbert Bayard, a first secretary to King Francis I, who had fiefs in Bourbonnais. In 1545, he accompanied the French envoy Louis Adhémar de Monteil, Count of Grignan, to the Diet of Worms as a junior secretary. After the diet's rupture, he traveled in Europe.Moreri 1759 vol. 10, p. 606 ("Vigenere, Blaise de") In 1547, he quit the court and entered the service of the House of Nevers. He would remain associated with it until at least a year before his death in 1596. At first ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tabula Recta
In cryptography, the ''tabula recta'' (from Latin language, Latin ''wikt:tabula#Latin, tabula wikt:rectus#Latin, rēcta'') is a square table of alphabets, each row of which is made by shifting the previous one to the left. The term was invented by the German author and monk Johannes TrithemiusSalomon, Data Privacy, page 63 in 1508, and used in his Trithemius cipher. Trithemius cipher The Trithemius cipher was published by Johannes Trithemius in his book ''Polygraphia (book), Polygraphia'', which is credited with being the first published printed work on cryptology. Trithemius used the ''tabula recta'' to define a polyalphabetic cipher, which was equivalent to Leon Battista Alberti's Alberti cipher disk, cipher disk except that the order of the letters in the target alphabet is not mixed. The ''tabula recta'' is often referred to in discussing pre-computer ciphers, including the Vigenère cipher and Blaise de Vigenère's less well-known autokey cipher. All polyalphabetic ciphe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American Cryptogram Association
The American Cryptogram Association (ACA) is an American non-profit organization devoted to the hobby of cryptography, with an emphasis on types of codes, ciphers, and cryptograms that can be solved either with pencil and paper, or with computers, but not computer-only systems. History The ACA was formed on September 1, 1930. Since some of its members had belonged to the “ National Puzzlers' League”, some of the NPL terminology ("nom," "Krewe," etc.) is also used in the ACA. Publications and activities The association has a collection of books and articles on cryptography and related subjects in the library at . An annual convention takes place in lat ...[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kasiski Examination
In cryptanalysis, Kasiski examination (also known as Kasiski's test or Kasiski's method) is a method of attacking polyalphabetic substitution ciphers, such as the Vigenère cipher. It was first published by Friedrich Kasiski in 1863, but seems to have been independently discovered by Charles Babbage as early as 1846. How it works In polyalphabetic substitution ciphers where the substitution alphabets are chosen by the use of a keyword, the Kasiski examination allows a cryptanalyst to deduce the length of the keyword. Once the length of the keyword is discovered, the cryptanalyst lines up the ciphertext in ''n'' columns, where ''n'' is the length of the keyword. Then each column can be treated as the ciphertext of a monoalphabetic substitution cipher. As such, each column can be attacked with frequency analysis. Similarly, where a rotor stream cipher machine has been used, this method may allow the deduction of the length of individual rotors. The Kasiski examination involves ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Index Of Coincidence
In cryptography, coincidence counting is the technique (invented by William F. Friedman) of putting two texts side-by-side and counting the number of times that identical letters appear in the same position in both texts. This count, either as a ratio of the total or normalized by dividing by the expected count for a random source model, is known as the index of coincidence, or IC or IOC or IoC for short. Because letters in a natural language are not letter frequency, distributed evenly, the IC is higher for such texts than it would be for uniformly random text strings. What makes the IC especially useful is the fact that its value does not change if both texts are scrambled by the same single-alphabet substitution cipher, allowing a cryptanalyst to quickly detect that form of encryption. Calculation The index of coincidence provides a measure of how likely it is to draw two matching letters by randomly selecting two letters from a given text. The chance of drawing a given letter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bigram
A bigram or digram is a sequence of two adjacent elements from a string of tokens, which are typically letters, syllables, or words. A bigram is an ''n''-gram for ''n''=2. The frequency distribution of every bigram in a string is commonly used for simple statistical analysis of text in many applications, including in computational linguistics, cryptography, and speech recognition. ''Gappy bigrams'' or ''skipping bigrams'' are word pairs which allow gaps (perhaps avoiding connecting words, or allowing some simulation of dependencies, as in a dependency grammar). Applications Bigrams, along with other n-grams, are used in most successful language models for speech recognition. Bigram frequency attacks can be used in cryptography to solve cryptograms. See frequency analysis. Bigram frequency is one approach to statistical language identification. Some activities in logology or recreational linguistics involve bigrams. These include attempts to find English words beginning wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trigram
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 ofLetter Frequencies in the English Language. Frequency Context is very important, varying analysis rankings and percentages are easily derived by drawing from different sample sizes, different authors; or different document types: poetry, science-fiction, technology documentation; and writing levels: stories for children versus adults, military orders, and recipes. Typical cryptanalytic frequency analysis finds that the 16 most common character-level trigrams in English are: Because encrypted messages sent by telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
