NationMaster - Encyclopedia: Vigenère cipher

The Vigenère cipher is a method of This article is about algorithms for encryption and decryption. For an overview of cryptographic technology related to encryption, see cryptography. In cryptography, encryption is the process of obscuring information to make it unreadable without special knowledge. While encryption has been used to protect communications for centuries, only organisations and individuals... encryption that uses a series of different The action of a Caesar cipher is to move each letter a number of places down the alphabet. This example is with a shift of three, so that a B in the plaintext becomes E in the ciphertext. In cryptography, a Caesar cipher, also known as a Caesar shift cipher... Caesar ciphers based on the letters of a keyword. It is a simplified version of the more general 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 first published polyalphabetic cipher was invented by Leon Battista Alberti around 1467. Alberti used a... polyalphabetic substitution cipher, invented by Leone Battista Alberti (February 1404 - 25th April 1472), Italian painter, poet, linguist, philosopher, cryptographer, musician, architect, and general Renaissance polymath . His life was described in Giorgio Vasaris Vite. In Italy, his first name is usually spelled Leon. Alberti was born in Genoa as an illegitimate son of a family... Alberti circa Events July 13 - Battle of Montlhéry - Troops of King Louis XI of France fight inconclusively against an army of the great nobles organized as the League of the Public Weal. Charles VIII of Sweden is deposed. Clergyman Kettil Karlsson Vasa becomes Regent of Sweden. August 11- Regent Kettil Karlsson... 1465.

The invention of the Vigenère cipher was misattributed to Blaise de Vigenère in the Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. In the sense of the Common Era... 19th century; it was originally described by a Giovan Batista Belaso in his Events June 26 - Christs Hospital in London gets a Royal Charter July 6 - Edward VI of England dies July 10 - Lady Jane Grey is proclaimed Queen of England - for the next nine days July 18 - Lord Mayor of London proclaims Queen Mary as the rightful Queen - Lady Jane Grey... 1553 book La cifra del. Sig. Giovan Batista Belaso.

This cipher is well-known because while it is easy to understand and implement, it often appears to beginners to be unbreakable. Consequently, many programmers have implemented In computing, obfuscation refers to the deliberate act of nondestructively changing either the source code of a computer program or machine code when the program is in some compiled or binary form, so that it is not easy to understand or read. Binary obfuscation is usually performed, preventing or making... obfuscation or encryption schemes in their applications which are essentially Vigenère ciphers, only to have them broken by the first cryptanalyst who comes along.

Description

In a The action of a Caesar cipher is to move each letter a number of places down the alphabet. This example is with a shift of three, so that a B in the plaintext becomes E in the ciphertext. In cryptography, a Caesar cipher, also known as a Caesar shift cipher... Caesar cipher, each letter of the alphabet is shifted along some number of places; for example, in a Caesar cipher of shift 3, A would become D, B would become E and so on. The Vigenère cipher consists of using several Caeser ciphers in sequence with different shift values.

To encipher, a table of alphabets can be used, termed a Tabula recta Tabula recta is a cryptographic term invented by Johannes Trithemius in 1518. The tabula recta was a square table of alphabets, each one made by shifting the previous one to the left, like this: Trithemius used the tabula recta to define a polyalphabetic cipher which was equivalent to... tabula recta or a Vigenère square. It consists of the alphabet written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet, corresponding to the 26 possible Caesar ciphers. At different points in the encryption, an encipherer uses a different alphabet from one of the rows. The alphabet used at each point depends on a repeating keyword.

For example, suppose the encipherer wishes to encrypt a In cryptography, plaintext is information used as input to an encryption algorithm; the output is termed ciphertext. The plaintext could be, for example, a diplomatic message, a bank transaction, an email, a diary and so forth — any information that someone might want to prevent others from reading. Plaintext is... plaintext:

The encipherer chooses a keyword and repeats it until it matches the length of the plaintext, for example, the keyword "LEMON":

The first letter of the plaintext, A, is enciphered using the alphabet in row L, which is the first letter of the key. This is done by looking at the letter in row L and column A of the Vigenère square, namely L. Similarly, for the second letter of the plaintext, the second letter of the key is used; the letter at row E and column T is X. The rest of the plaintext is enciphered in a similar fashion:

Decryption is performed by finding the position of the ciphertext letter in a row of the table, and then taking the label of the column in which it appears as the plaintext. For example, in row L, the ciphertext L appears in column A, which taken as the first plaintext letter. The second letter is decrypted by looking up X in row E of the table; it appears in column T, which is taken as the plaintext letter.

Vigenère can also be viewed algebraically. If the letters A–Z are taken to be the numbers 0–25, and addition is performed Modular arithmetic is a modified system of arithmetic for integers, sometimes referred to as clock arithmetic, where numbers wrap around after they reach a certain value (the modulus). For example, whilst 8 + 6 equals 14 in conventional arithmetic, in modulo 12 arithmetic the answer is two, as two is the... modulo 26, then Vigenère encryption can be written,

Cryptanalysis

Main article: In cryptanalysis, the Kasiski examination or Kasiski test is a method of attacking polyalphabetic substitution ciphers, such as Vigenere ciphers. It was developed by Friedrich Kasiski. The Kasiski examination allows a cryptanalyst to deduce the length of the keyword used in the polyalphabetic substitution cipher. Once the length of the... Kasiski examination

The method described below was not in fact invented by Kasiski but instead by Charles Babbage Charles Babbage ( December 26, 1791 – October 18, 1871) was an English mathematician, analytical philosopher and (proto-) computer scientist who was the first person to come up with the idea of a programmable computer. Parts of his uncompleted mechanisms are on display in the London Science Museum. In... Charles Babbage; its attribution to Kasiski is a common misconception.

The idea behind the Vigenère cipher is like that of all polyalphabetic ciphers — to make In mathematics, physics and signal processing, frequency analysis is a method to decompose a function, wave, or signal into its frequency components so that it is possible to have the frequency spectrum. A typical distribution of letters in English language text. Weak ciphers do not sufficiently mask the distribution, and... frequency analysis more difficult. Frequency analysis is the practice of decrypting a message by counting the frequency of ciphertext letters, and equating it to the letter frequency of normal text. For instance if P occurred most in a ciphertext whose plaintext is in The English language is a West Germanic language that originates in England. It is the third most common first language (native speakers), with around 402 million people in 2002. English has lingua franca status in many parts of the world, due to the military, economic, scientific, political and cultural influence... English one could suspect that P corresponded to E, because E is the most frequently used letter in English. Using the Vigenère cipher, E can be enciphered as any of several letters in the alphabet at different points in the message thus defeating simple frequency analysis.

Noted author and mathematician Charles Ludwidge Dodgson (aka Photograph of Lewis Carroll taken by himself, with assistance Charles Lutwidge Dodgson (January 27, 1832 – January 14, 1898), better known by the pen name Lewis Carroll, was a British author, mathematician, Anglican clergyman, logician, and amateur photographer. His most famous writings are Alices Adventures in Wonderland and its... Lewis Carroll) called this cipher unbreakable in his 1868 was a leap year starting on Wednesday (see link for calendar). Events January 3 - Meiji Emperor declares Meiji Restoration, his own restoration to full power, against the supporters of the Tokugawa Shogunate. January 10 - Shogun Tokugawa Yoshinobu declares emperors declaration illegal and attacks Kyoto. Pro-Emperor forces drive... 1868 piece " Lewis Carroll published The Alphabet-Cipher in 1868, possibly in a childrens magazine. It describes what is known as a Vigenère cipher, a well-known scheme in cryptography. It is amusing to note that while Carroll calls this cipher unbreakable, Kasiski had published a volume describing how to... The Alphabet Cipher" in a children's magazine. In 1917 was a common year starting on Monday (see link for calendar). Events January-February President Woodrow Wilson of the United States announces to Congress the breaking of diplomatic relations with Germany January 2 - The Royal Bank of Canada takes over Quebec Bank. January 22 - World War I: President Woodrow... 1917, the Vigenère was described as "impossible of translation" in the respected science magazine Scientific American is one of the oldest and most serious popular-science magazines. Founded by Rufus Porter, Scientific American has been published monthly since August 28, 1845. Among science periodicals, Scientific American (informally abbreviated to Sciam) is the most widely read, bringing authoritatively written articles about highly new and innovative... Scientific American. Despite this reputation, however, the cipher can be broken.

The weakness lies with the fact that the key is relatively short and constantly repeated: as a result, common words like "the" will likely be encrypted using the same key letters, leading to repeated groups in the ciphertext. Look at this example:

The encrypted text here will not have repeated sequences that correspond to repeated sequences in the plaintext. However, if the key length is different, as in this example:

Then a In cryptanalysis, the Kasiski examination or Kasiski test is a method of attacking polyalphabetic substitution ciphers, such as Vigenere ciphers. It was developed by Friedrich Kasiski. The Kasiski examination allows a cryptanalyst to deduce the length of the keyword used in the polyalphabetic substitution cipher. Once the length of the... Kasiski examination can be used.

The cipher of Blaise de Vigenère

Vigenère actually invented a stronger cipher: an An autokey cipher, or self-synchronizing stream cipher, is a cipher which incorporates the message (the plaintext) into the key. 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... autokey cipher. The name "Vigenère cipher" became associated with this polyalphabetic cipher instead. In fact the two ciphers were often confused, and both were sometimes called "le chiffre indéchiffrable", or "the unbreakable cipher". For nearly 300 years this cipher was thought to be unbreakable, but Charles Babbage Charles Babbage ( December 26, 1791 – October 18, 1871) was an English mathematician, analytical philosopher and (proto-) computer scientist who was the first person to come up with the idea of a programmable computer. Parts of his uncompleted mechanisms are on display in the London Science Museum. In... Charles Babbage and Major Friedrich Wilhelm Kasiski (29 November 1805 - 22 May 1881) was a Prussian infantry officer, cryptographer and archeologist. Kasiski was born in Schlochau, West Prussia (now Czluchow, Poland). Military service Kasiski enlisted in East Prussias 33rd Infantry Regiment on 20 March 1823 at the age of 17. In May... Friedrich Kasiski independently found a way to break it the middle of the 19th century. Babbage actually broke the much stronger autokey cipher, while Kasiski is generally credited with the first published solution to fixed-key polyalphabetic ciphers.

External links

Classical cryptography edit (http://en.wikipedia.org/w/index.php?title=Template:Classical_cryptography&action=edit)

Ciphers: In cryptography, the ADFGVX cipher was a field cipher used by the German Army during World War I. ADFGVX was in fact an extension of an earlier cipher called ADFGX. Invented by Colonel Fritz Nebel and introduced in March 1918, the cipher was a fractionating transposition cipher which combined a... ADFGVX | The Affine cipher is a special case of the more general substitution cipher. It is monoalphabetic and symmetric. In affine ciphers the encryption function for a letter is where, and are coprime (otherwise would have no multiplicative inverse modulo ). is the size of the alphabet. The decryption function is where... Affine | Atbash is a simple substitution cipher in Hebrew. It consists of substituting aleph (the first letter) for tav (the last), beth (the second) for shin (one before last), and so on, reversing the alphabet. A couple of words in the Book of Jeremiah, Leb Kamai and Sheshakh, are atbash for... Atbash | An autokey cipher, or self-synchronizing stream cipher, is a cipher which incorporates the message (the plaintext) into the key. 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... Autokey | In classical cryptography, the bifid cipher is a cipher which combines the Polybius square with transposition, and uses fractionation to achieve diffusion. It was invented around 1901 by Felix Delastelle. Operation First, a mixed alphabet Polybius square is drawn up: 1 2 3 4 5 1 B G W K... Bifid | A book cipher is a cipher in which the key is the identity of a book. Traditionally book ciphers work by replacing words in the plaintext of a message with the location of words from a book. In this mode, book cyphers are more properly called codes. This can have... Book | The action of a Caesar cipher is to move each letter a number of places down the alphabet. This example is with a shift of three, so that a B in the plaintext becomes E in the ciphertext. In cryptography, a Caesar cipher, also known as a Caesar shift cipher... Caesar | Four-square | Hills 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... Hill | In classical cryptography, a permutation cipher is a transposition cipher in which the key is a permutation. To apply a cipher, a random permutation of size e is generated (the larger the value of e the more secure the cipher). The plaintext is then broken into segments of size e... Permutation | The Pigpen Cipher is a simple substitution cipher exchanging letters for symbols, using a grid. Grid A | B | C J.| K.| L. S / W./ ---+---+--- ---+---+--- / / D | E | F M.| N.| O. T X U X. X Y. ---+---+--- ---+---+--- / / G | H | I P.| Q.| R. / V / Z. Encryption It is then used by... Pigpen | The Playfair system was invented by Charles Wheatstone, first described in 1854. The Playfair cipher or Playfair square is a manual symmetric encryption technique and was the first literal digraph substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair who promoted... Playfair | 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 first published polyalphabetic cipher was invented by Leon Battista Alberti around 1467. Alberti used a... Polyalphabetic | Reihenschieber | In classical cryptography, the runnning key cipher is a type of polyalphabetic substitution cipher in which a text, typically from a book, is used to provide a very long key stream. Usually, the book to be used would be agreed ahead of time, while the passage to use would be... Running key | In cryptography, a substitution cipher is a method of encryption by which units of plaintext are substituted with ciphertext according to a regular system; the units may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the... Substitution | In classical cryptography, a transposition cipher changes one character from the plaintext to another (to decrypt the reverse is done). That is, the order of the characters is changed. Mathematically a bijective function is used on the characters positions to encrypt and an inverse function to decrypt. Following are some... Transposition | In classical cryptography, the trifid cipher is a cipher invented around 1901 by Felix Delastelle, which extends the concept of the bifid cipher to a third dimension, allowing each symbol to be fractionated into 3 elements instead of two. That is, while the bifid uses the Polybius square to turn... Trifid | Two-square | Vigenère

Cryptanalysis: In mathematics, physics and signal processing, frequency analysis is a method to decompose a function, wave, or signal into its frequency components so that it is possible to have the frequency spectrum. A typical distribution of letters in English language text. Weak ciphers do not sufficiently mask the distribution, and... Frequency analysis | 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 a letter appears next to itself in both copies. This count, as a ratio of the total, is known as the index of coincidence... Index of coincidence Misc: A cryptogram is a type of word puzzle popularly printed in some newspapers and magazines. A short piece of text is given, encrypted with a simple substitution cipher in which each letter is replaced by a different letter. To solve the puzzle, one must recover the plaintext; this is usually... Cryptogram | In cryptography, the Polybius square is a device invented by the Ancient Greek historian and scholar Polybius, for fractionating plaintext characters so that they can be represented by a smaller set of symbols. Basic form In typical form, it appears thus: Each letter is then represented by its co-ordinates... Polybius square | This article is about the encryption device; for the Dune character, see Scytale (Dune). In cryptography, a scytale (also transliterated as skytale) is a tool used to perform a transposition cipher, consisting of a cylinder with a strip of paper wound around it on which is written a message. The... Scytale | In cryptography, a straddling checkerboard is a device for converting an alphabetic plaintext into digits whilst simultaneously achieving fractionation (a simple form of information diffusion) and homophony (a simple method for suppressing peaks of the frequency distribution). A straddling checkerboard is set up something like this: The first row is... Straddling checkerboard | Tabula recta Tabula recta is a cryptographic term invented by Johannes Trithemius in 1518. The tabula recta was a square table of alphabets, each one made by shifting the previous one to the left, like this: Trithemius used the tabula recta to define a polyalphabetic cipher which was equivalent to... Tabula recta

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Cryptanalysis

The cipher of Blaise de Vigenère

External links

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