
	Where results make sense

Topic: Polyalphabetic substitution

Related Topics

Monoalphabetic substitution cipher

Playfair cipher

Frequency analysis

Cryptographer

List of famous ciphertexts

Blowfish (cipher)

Topics in cryptography

Witham

1523

In the News (Mon 7 Dec 09)

Northern Trust

Marvin Harrison

Peter Chernin

Gary Locke

Match Play

Penelope Cruz

Mickey Rourke

AR Rahman

Danny Boyle

Hugh Jackman

	Polyalphabetic cipher - Wikipedia, the free encyclopedia
		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.
		Polyalphabetic substitution cipher designers seem to have concentrated on obscuring the choice of a few such alphabets (repeating as needed), not on the increased security possible by using many and never repeating any.
	en.wikipedia.org /wiki/Polyalphabetic_cipher (507 words)

	Substitution cipher - Wikipedia, the free encyclopedia
		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.
		Polyalphabetic substitution ciphers were first described in 1467 by Leone Battista Alberti in the form of disks.
		A digraphic substitution is then simulated by taking pairs of letters as two corners of a rectangle, and using the other two corners as the ciphertext (see the Playfair cipher main article for a diagram).
	en.wikipedia.org /wiki/Substitution_cipher (2600 words)

	NaTa2.info .:[/misc/phrack/phrack62/p62-0x0e_A_Polyalphabetic_Substitution_Cipher.txt]:. NaTa2.info (Site not responding. Last check: 2007-10-31)
		Polyalphabetic substitution is an hybrid between transposition and substitution.
		While this sounds stronger than transposition and substitution, it is still very weak and unless a RNG is used to generate a key that is as long as the data to encrypt (one-time pad), it is possible to recover the key size, the key itself and/or the message with enough data to analyze.
		Polyalphabetic substitution as described above is vulnerable to chosen texts attack, known texts attack, key correlation attack and eventually statistical attacks.
	www.nata2.info /?path=misc/phrack/phrack62&text=p62-0x0e_A_Polyalphabetic_Substitution_Cipher.txt (4103 words)

	Background
		Substitution ciphers are characterized by a substitution of a character in the original plain text messageby the corresponding character in the cipher alphabet, often according to some protocol derived from a predetermined key.
		In a monoalphabetic substitution cipher a single character in the plaintext alphabet is replaced by a single character in the cipher alphabet.
		A polyalphabetic substitution cipher is fairly similar to a monalphabetic one, the difference being that instead of using a single cipher alphabet, multiple cipher alphabets are used.The simplest type of polyalphabetic cipher, the Vigenere cipher, can use as many as twenty-six distinct cipher alphabets, each a simple rotation of the normally ordered alphabet.
	www.cs.unc.edu /~stotts/COMP145/homes/crypt/userManual/user_back.html (1392 words)

	Cryptography/Polyalphabetic substitution - Wikibooks, collection of open-content textbooks
		A Polyalphabetic substitution cipher is simply a substitution cipher with an alphabet that changes.
		Polyalphabetic substitution ciphers are useful because the are less easily broken by frequency analysis, however if an attacker knows for instance that the message has a period n, then he simply can individually frequency analyze each cipher alphabet.
		The number of letters encrypted before a polyalphabetic substitution cipher returns to its first cipher alphabet is called its period.
	en.wikibooks.org /wiki/Cryptography:Polyalphabetic_substitution (209 words)

	Vigenère cipher - Wikipedia, the free encyclopedia
		It is a simple form of polyalphabetic substitution.
		The first polyalphabetic cipher, created by Leone Battista Alberti around 1467, used a metal cipher disc to switch between cipher alphabets.
		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.
	en.wikipedia.org /wiki/Vigen%c3%a8re_Cipher (2103 words)

	NSNL 10 - Polyalphabetic substitution ciphers
		In polyalphabetic substitution the cleartext letters are enciphered differently depending upon their placement in the text.
		As the name polyalphabetic suggests this is achieved by using several cryptoalphabets instead of just one, as is the case in most of the simpler crypto systems.
		The most common polyalphabetic substitution cipher is the Vigenère or, as it is sometimes referred to, Tritheim's system.
	www.cvni.net /radio/nsnl/nsnl010/nsnl10poly.html (1044 words)

	[2.0] Refining The Art
		For example, two substitution cipher alphabets could be defined and used on alternating letters of a plaintext, with all the even-numbered letters enciphered by one cipher alphabet and all the odd-numbered letters enciphered by the other.
		The idea of such a "polyalphabetic substitution cipher" was refined for over a century, until a French diplomat named Blaise de Vigenere turned it into the simple and elegant cipher scheme that bears his name.
		The basic concept is to use multiple substitution symbols for each letter, with the number of substitutions proportional to the frequency of the letter.
	www.vectorsite.net /ttcode_02.html (3082 words)

	CRYPTOGRAPHY IN ANTIQUITY TO WW-I (Site not responding. Last check: 2007-10-31)
		In most cases in this era the substitution process was fixed per letter; that is if the letter g was substituted by k in one appearance, it was substituted by k for all other appearances.
		The fact is that even today when monoalphabetic substitution is obsolete for any serious business, it is live and well in the world of entertainment, and a large variety thereof is found in form of puzzles, riddles in most respected dailies and magazines.
		The polyalphabetic variety, was a one-to-many option in terms of replacing the same plaintext letter with a different (or same) letter each time.
	www.tryagain.com /infocomm/cryptold.htm (2016 words)

	Cryptography Tutorial - Substitution Ciphers
		Example 1: (Caesar Cipher) The simplest of all substitution ciphers is the one in which the cipher letters results from shifting plain letters by the same distance.
		In Substitution Ciphers, single letters or pairs of letters are replaced with symbols or groups of symbols, which need not be the same as those used in the plaintext.
		When this "polyalphabetic substitution" is carried to its limit, it results in socalled "onetime pads", which are the only cryptosystems that can be proved to be secure.
	www.antilles.k12.vi.us /math/cryptotut/substitution.htm (1335 words)

	Photo Album
		One of the main problems with simple substitution ciphers is that they are so vulnerable to frequency analysis.
		A polyalphabetic substitution cipher involves the use of two or more cipher alphabets.
		Instead of there being a one-to-one relationship between each letter and its substitute, there is a one-to-many relationship between each letter and its substitutes.
	www.angelfire.com /droid/cryptography/experiment.htm (551 words)

	COMS 4180 Project \| Michael E. Locasto
		Polyalphabetic substitution ciphers seek to frustrate the type of statistical analysis of ciphertext that can easily be performed on monoalphabetic substitution ciphers.
		Polyalphabetic substitution ciphers will flatten the frequency distribution of the ciphertext, making it more difficult to match letters.
		The main idea in decoding polyalphabetic substitution ciphers is to determine the number of alphabets used in the ciphertext and then split the ciphertext into pieces corresponding to those alphabets.
	www1.cs.columbia.edu /~locasto/CompSci/COMS4180/paper.html (2415 words)

	Codes and Ciphers
		The Caesar Substitution cipher, and all like it were called "simple substitution" (to the cryptologist, "monalphabetic substitution") because throughout the message, each character was always replaced by the identical cipher character (e.g., in the Caesar Substitution, "F" would always represent "c" throughout the message).
		An invention by Leon Battista Alberti, an Italian, in the 15th Century, both refined simple substitution ciphers and started a more complex form, known as "polyalphabetic substitution," which is the key to modern methods.
		This polyalphabetic substitution scheme, and other, more complex forms than Alberti developed, form the basis of modern high-security cryptological messaging.
	www.otr.com /ciphers.shtml (2124 words)

	Polyalphabetic cipher
		The Vigenère's cipher is probably the best-known example of a polyalphabetic cipher, though it is only a special case.
		The disk started with A underneath B, and the user rotated the disk by one letter after encrypting each letter.
		Trithemius' cypher was trivial to break, and Alberti's not much more difficult (the capitalized letter is a major clue to the cryptanalyst), but they laid the groundwork for future ciphers using the powerful ideas of polyalphabeticity and key progression.
	www.ebroadcast.com.au /lookup/encyclopedia/po/Polyalphabetic_substitution.html (347 words)

	Leone Battista Alberti - tScholars.com (Site not responding. Last check: 2007-10-31)
		Alberti was an accomplished cryptographer by the standard of his day, and invented both polyalphabetic ciphers and machine-assisted encryption using his Cipher Disk.
		The polyalphabetic cipher was, at least in principle, for it was not properly used for several hundred years, the most significant advance in cryptography since before Julius Caesar's time.
		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" (The Codebreakers, 1967).
	www.tscholars.com /encyclopedia/Leone_Battista_Alberti (826 words)

	Polyalphabetic Substitution (Site not responding. Last check: 2007-10-31)
		The idea of using substitution ciphers that change during the course of a message was a very important step forwards in cryptography.
		Incidentally, for the polyalphabetic encryption of a stream of message digits by a stream of key digits, it is not strictly necessary to use only addition without carries.
		Since it is only required that the operation table for polyalphabetic combining of a keystream with text be a Latin square for it to function in an ideal fashion, it is not necessary that the table be patterned after that for a group; but groups certainly are a common source of tables.
	www.quadibloc.com /crypto/pp010303.htm (6453 words)

	Polyalphabetic Substitution Ciphers
		To find the substitution letter, trace the column of the key letter down to the row of the plain text letter and use the letter found in this cell.
		The substitution letter is found in the first row of this column.
		As for the other polyalphabetic substitution ciphers you may choose one of the operation modes.
	members.aon.at /cipherclerk/Doc/Vigenere.html (839 words)

	Entry King:1994:ACA from cryptologia.bib
		Probabilistic relaxation is then extended to solve polyalphabetic ciphers without word divisions and of unknown key periods in a ciphertext-only attack.
		polyalphabetic, 11(4)193, 14(2)128, 14(3)199, 18(4)356, 19(3)265, 20(3)247, 21(2)129
		substitution, 4(2)109, 7(2)z-2, 7(z)170, 8(4)z-4, 9(2)z-1, 10(1)z-4, 10(4)193, 13(1)61, 14(4)289, 14(4)355, 15(3)258, 16(3)215, 16(3)282, 17(1)31, 17(2)148, 17(2)172, 17(2)202, 17(3)225, 17(4)407, 19(3)265, 20(3)247, 21(2)129
	www.math.utah.edu /ftp/pub/tex/bib/idx/cryptologia/18/4/332-355.html (527 words)

	[No title] (Site not responding. Last check: 2007-10-31)
		Polyalphabetic substitution systems consists of two general types; periodic and non-periodic.
		He is credited with a revolutionary insight regarding polyalphabetic repeating key systems - that the conjuction of a repeated portion of the key with the repetition in the plaintext produces a repetition in the ciphertext.
		The interval between plaintext or ciphertext repetitions is noted throughout the cryptogram, factored and the commonality of the factor is a good indication of the key and number of alphabets used to encipher the original methods.
	www.math.utoledo.edu /~codentha/Cryptanalysis/lanaki/lanaki10.txt (10921 words)

	Cryptography Workshop Outline
		A simple shift uses a one-element key, and the cipher is broken by fixing just one letter; an affine code uses a two-element key and may be broken by fixing as few as two letters; a word-key substitution cipher has a variable-length key, and requires more work to break.
		An astonishingly simple machine implements a substitution cipher in which the alphabets move irregularly, and the cycle of alphabets is the GCD of the sizes of two wheels.
		Gaines describes many of the classic transposition and substitution ciphers, and provides detailed instructions for their cryptanalysis.
	www.mtholyoke.edu /courses/quenell/s2002/crypto/outline.html (1561 words)

	Cryptography -- Vigenere Cipher
		Thus, any message encrypted by a Vigenere cipher is a collection of as many simple substitution ciphers as there are letters in the keyword.
		Vigenere-like substitution ciphers were regarded by many as practically unbreakable for 300 years.
		Given the structure of the Vigenere tableau, this is equivalent to using 9 distinct simple substitution ciphers, each of which was derived from 1 of the 26 possible Caesar shifts given in the tableau.
	www.trincoll.edu /depts/cpsc/cryptography/vigenere.html (1337 words)

	Improving Substitution (Site not responding. Last check: 2007-10-31)
		Instead of using the same set of substitutes all the time, change from one secret alphabet to another as you encipher a message (polyalphabetic substitution).
		Before that, other representations of text were used to substitute for the printed word, such as Morse code.
		This is called fractionation, and is closely related to polygraphic substitution for two reasons; one is that both deal with different sized units - parts of letters and letters, or letters and pairs of letters - and the other is that fractionation is sometimes used as a method of polygraphic substitution.
	www.quadibloc.com /crypto/pp0103.htm (366 words)

	CS 513 System Security -- Introduction to Cryptography
		Another--somewhat stronger, cryptographically--example of a monoalphabetic substitution cipher is to use an arbitrary permutation of the alphabet, rather than shifting by a certain number.
		The problem with monoalphabetic substitution ciphers is that the preservation of alphabet distributions makes them vulnerable to frequency-based attacks.
		In a polyalphabetic substitution, it is likely that 'th' will be permuted using permutations 1 and 2 at multiple points.
	www.cs.cornell.edu /Courses/cs513/2000SP/L23.html (1254 words)

	frequency analysis
		In the field of cryptanalysis, frequency analysis is a method for "breaking" simple substitution ciphers, like the Caesar cipher.
		These cyphers replace one letter of the plaintext with another to produce the cyphertext, and any particular letter in the plaintext will always, in the simplest and most easily breakable of these cyphers, turn into the same letter in the cypher.
		Poe was overconfident in his proclamation, however, for polyalphabetic substitution ciphers (invented by Alberti around 1467) are immune to simple frequency analysis attacks.
	www.textalyser.net /frequency_analysis.html (716 words)

	Lesson 0.5: Polyalphabetic Ciphers
		The idea behind the polyalphabetic cipher is that a single letter can be encrypted to several different letters instead of just one.
		We will study the Vigenere Cipher, which is a polyalphabetic substitution cipher.
		There are two ways to use this square to form a polyalphabetic cipher.
	math.usask.ca /encryption/lessons/lesson00/page5.html (493 words)

	CS 180 (Spring 2003) Project #4 (Site not responding. Last check: 2007-10-31)
		Since the letter from the plaintext is letter 5 of the alphabet, the encrypted version of this letter is the letter found in the fifth element of the substitution map.
		With this map, if the plaintext letter was C (letter 3 in the alphabet), the encrypted version would be found in the third element in the substitution map (since Java uses zero-indexed arrays, the third element is array index 2) which is X.
		Repeat this procedure until all letters of the plaintext message have been encrypted OR you run out of substitution maps (keep in mind that the message may be longer than the number of substitution maps you are given).
	web.ics.purdue.edu /~cs180/Spring2003Web/projects/proj4/project4.html (934 words)

	CPT 123 - Fall 1998 - Assignment Five (Site not responding. Last check: 2007-10-31)
		Julius Caesar is given credit for developing one of the oldest polyalphabetic substitution cipher encryption schemes.
		Caesar used a simple substitution algorithm in which each letter in the original text was replaced by the letter three positions further in the alphabet.
		The original word "cat" would be encrypted as "fdw." It was simple, but it worked as long as the sender and the recipient knew the key [the number of letters to shift forward in the alphabet].
	www.engr.iupui.edu /~williams/cpt123/1999sp/123asign05.html (194 words)

Try your search on: Qwika (all wikis)