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Information about Classical Cipher

In cryptography, a classical cipher is a type of cipher used historically but which now have fallen, for the most part, into disuse. In general, classical ciphers operate on an alphabet of letters (such as "A-Z"), and are implemented by hand or with simple mechanical devices. By contrast, modern schemes use computers or other digital technology, and operate on bits and bytes. Classical schemes are often susceptible to ciphertext-only attacks, sometimes even without knowledge of the system itself, using tools such as frequency analysis. Sometimes classed with classical ciphers are more advanced mechanical or electro-mechanical cipher machines, such as the Enigma machine.

Classical ciphers are often divided into transposition ciphers and substitution ciphers. In a substitution cipher, letters (or groups of letters) are systematically replaced throughout the message for other letters (or groups of letters). For instance a simple (and therefore easy to crack) encryption would be to substitute each letter for the next letter in the alphabet (a to b, b to c, and so on with z being substituted by a). Using this encryption the sentence "Hello my name is Bob." would be encrypted as "Ifmmp nz obnf jt Cpc."

It is possible to list all substitution ciphers where the order of the alphabet is preserved on a grid such that each column holds every possible substitution for the letter on the first row of that column. This is shown here:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
BCDEFGHIJKLMNOPQRSTUVWXYZA
CDEFGHIJKLMNOPQRSTUVWXYZAB
DEFGHIJKLMNOPQRSTUVWXYZABC
EFGHIJKLMNOPQRSTUVWXYZABCD
FGHIJKLMNOPQRSTUVWXYZABCDE
GHIJKLMNOPQRSTUVWXYZABCDEF
HIJKLMNOPQRSTUVWXYZABCDEFG
IJKLMNOPQRSTUVWXYZABCDEFGH
JKLMNOPQRSTUVWXYZABCDEFGHI
KLMNOPQRSTUVWXYZABCDEFGHIJ
LMNOPQRSTUVWXYZABCDEFGHIJK
MNOPQRSTUVWXYZABCDEFGHIJKL
NOPQRSTUVWXYZABCDEFGHIJKLM
OPQRSTUVWXYZABCDEFGHIJKLMN
PQRSTUVWXYZABCDEFGHIJKLMNO
QRSTUVWXYZABCDEFGHIJKLMNOP
RSTUVWXYZABCDEFGHIJKLMNOPQ
STUVWXYZABCDEFGHIJKLMNOPQR
TUVWXYZABCDEFGHIJKLMNOPQRS
UVWXYZABCDEFGHIJKLMNOPQRST
VWXYZABCDEFGHIJKLMNOPQRSTU
WXYZABCDEFGHIJKLMNOPQRSTUV
XYZABCDEFGHIJKLMNOPQRSTUVW
YZABCDEFGHIJKLMNOPQRSTUVWX | Z | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y


In a transposition cipher, the letters themselves are kept unchanged, but their order within the message is scrambled according to some well-defined scheme. A simple (and once again easy to crack) encryption would be to write every word backwards. For example "Hello my name is Bob." would now be "olleH ym eman si boB."

More complex algorithms can be formed by mixing substitution and transposition in a product cipher; modern block ciphers such as DES iterate through several stages of substitution and transposition.

See also

External links

Classical cryptography
 •  • [ e]
Ciphers: ADFGVX | Affine | Alberti | Atbash | Autokey | Bifid | Book | Caesar | Four-square | Hill | Keyword | Nihilist | Permutation | Pigpen | Playfair | Polyalphabetic | Polybius | Rail Fence | Reihenschieber | Reservehandverfahren | ROT13 | Running key | Scytale | Smithy code | Solitaire | Straddling checkerboard | Substitution | Tap Code | Transposition | Trifid | Two-square | VIC cipher | Vigenre
Cryptanalysis: Frequency analysis | Index of coincidence
Misc: Cryptogram | Bacon | Polybius square | Scytale | Straddling checkerboard | Tabula recta
Cryptography
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History of cryptography | Cryptanalysis | | Topics in cryptography
Symmetric-key algorithm | Block cipher | Stream cipher | Public-key cryptography | Cryptographic hash function | Message authentication code | Random numbers
Cryptography (or cryptology; derived from Greek κρυπτός kryptós "hidden," and the verb γράφω gráfo "write" or λεγειν legein
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computer is a machine which manipulates data according to a list of instructions.

Computers take numerous physical forms. The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1941), although the computer concept and various machines
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BIT is an acronym for:
  • Bannari amman Institute of Technology
  • Bangalore Institute of Technology
  • Beijing Institute of Technology
  • Benzisothiazolinone
  • Bilateral Investment Treaty
  • Bhilai Institute of Technology - Durg

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byte (pronounced /baɪt/) is a unit of measurement of information storage, most often consisting of eight bits. In many computer architectures it is a unit of memory addressing.
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In cryptography, a ciphertext-only attack (COA) is an attack model for cryptanalysis where the attacker is assumed to have access only to a set of ciphertexts.

The attack is completely successful if the corresponding plaintexts can be deduced, or even better, the key.
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frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers.

Frequency analysis is based on the fact that, in any given stretch of written language, certain letters and
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Enigma cipher machine
  • Enigma machine
  • Enigma rotor details
  • Cryptanalysis of the Enigma
  • Cyclometer

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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.
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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
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In cryptography, a product cipher is a popular type of block cipher that works by executing in sequence a number of simple transformations such as substitution, permutation, and modular arithmetic.
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block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. When encrypting, a block cipher might take a (for example) 128-bit block of plaintext as input, and output a corresponding 128-bit block
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Data Encryption Standard
The Feistel function (F function) of DES

General
IBM
1975 (standardized on January 1977)

Lucifer
Triple DES, G-DES, DES-X, LOKI89, ICE

Cipher detail
Key size(s):| 56 bits

Block size(s):| 64 bits
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The history of cryptography begins thousands of years ago. Until recent decades, it has been the story of what might be called classic cryptography — that is, of methods of encryption that use pen and paper, or perhaps simple mechanical aids.
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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
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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 ).

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The Alberti Cipher was the first ever Polyalphabetic Cipher.

Created in the late 15th century, circa.1470, by Leon Battista Alberti, it was the peak of cryptography at that time.
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Atbash is a simple substitution cipher for the Hebrew alphabet. 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.
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autokey cipher (also known as the autoclave cipher)[1] 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.
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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.
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A book cipher is a cipher in which the key is the identity of a book or other piece of text. It is generally essential that both correspondents not only have the same book, but the same edition.
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Caesar cipher, also known as a Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques.
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The Four-square cipher is a manual symmetric encryption technique. It was invented by famous French cryptographer Felix Delastelle.

The technique encrypts pairs of letters (digraphs
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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.
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A keyword is a monoalphabetic substitution. A keyword is thought of and then the letters of the alphabet are assigned a letter after the keyword has been decided. When the number of letters in the keyword has been assigned their encoded version, the rest of the alphabet is added to
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In the history of cryptography, the Nihilist cipher is a manually operated symmetric encryption cipher originally used by Russian Nihilists in the 1880s to organise terrorism against the czarist regime.
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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).
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pigpen cipher (sometimes called the masonic cipher or Freemason's cipher) is a simple substitution cipher exchanging letters for symbols based on a grid. The use of symbols is no impediment to cryptanalysis however, and cryptanalysis is identical to that of other
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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 the use of the cipher.
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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.
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In cryptography, the Polybius square, also known as the Polybius checkerboard, is a device invented by the Ancient Greek historian and scholar Polybius, described in Hist. X.45.6 ff.
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