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Caesar cipher

Caesar cipher, is one of the simplest and most widely known encryption techniques. The transformation can be represented by aligning two alphabets, the cipher alphabet is the plain alphabet rotated left or right by some number of positions.

When encrypting, a person looks up each letter of the message in the 'plain' line and writes down the corresponding letter in the 'cipher' line. Deciphering is done in reverse.
The encryption can also be represented using modular arithmetic by first transforming the letters into numbers, according to the scheme, A = 0, B = 1,..., Z = 25. Encryption of a letter x by a shift n can be described mathematically as

Plaintext: chiodo
cipher variations:
dijpep ejkqfq fklrgr glmshs hmntit
inouju jopvkv kpqwlw lqrxmx mrsyny
nstzoz otuapa puvbqb qvwcrc rwxdsd
sxyete tyzfuf uzagvg vabhwh wbcixi
xcdjyj ydekzk zeflal afgmbm bghncn

Decryption is performed similarly,

(There are different definitions for the modulo operation. In the above, the result is in the range 0...25. I.e., if x+n or x-n are not in the range 0...25, we have to subtract or add 26.)
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Atbash Cipher

Atbash is an ancient encryption system created in the Middle East. It was originally used in the Hebrew language.
The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards.
The first letter is replaced with the last letter, the second with the second-last, and so on.
An example plaintext to ciphertext using Atbash:
Plain: chiodo
Cipher: xsrlwl

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Baconian Cipher

To encode a message, each letter of the plaintext is replaced by a group of five of the letters 'A' or 'B'. This replacement is done according to the alphabet of the Baconian cipher, shown below.
a   AAAAA   g    AABBA     m    ABABB   s    BAAAB     y    BABBA
b   AAAAB   h    AABBB     n    ABBAA   t    BAABA     z    BABBB
c   AAABA   i    ABAAA     o    ABBAB   u    BAABB 
d   AAABB   j    BBBAA     p    ABBBA   v    BBBAB
e   AABAA   k    ABAAB     q    ABBBB   w    BABAA
f   AABAB   l    ABABA     r    BAAAA   x    BABAB

Plain: chiodo

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Affine Cipher
In the affine cipher the letters of an alphabet of size m are first mapped to the integers in the range 0..m - 1. It then uses modular arithmetic to transform the integer that each plaintext letter corresponds to into another integer that correspond to a ciphertext letter. The encryption function for a single letter is

where modulus m is the size of the alphabet and a and b are the key of the cipher. The value a must be chosen such that a and m are coprime.
Considering the specific case of encrypting messages in English (i.e. m = 26), there are a total of 286 non-trivial affine ciphers, not counting the 26 trivial Caesar ciphers. This number comes from the fact there are 12 numbers that are coprime with 26 that are less than 26 (these are the possible values of a). Each value of a can have 26 different addition shifts (the b value) ; therefore, there are 12*26 or 312 possible keys.
Plaintext: chiodo
cipher variations:

The decryption function is

where a - 1 is the modular multiplicative inverse of a modulo m. I.e., it satisfies the equation

The multiplicative inverse of a only exists if a and m are coprime. Hence without the restriction on a decryption might not be possible. It can be shown as follows that decryption function is the inverse of the encryption function,

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ROT13 Cipher
Applying ROT13 to a piece of text merely requires examining its alphabetic characters and replacing each one by the letter 13 places further along in the alphabet, wrapping back to the beginning if necessary. A becomes N, B becomes O, and so on up to M, which becomes Z, then the sequence continues at the beginning of the alphabet: N becomes A, O becomes B, and so on to Z, which becomes M. Only those letters which occur in the English alphabet are affected; numbers, symbols, whitespace, and all other characters are left unchanged. Because there are 26 letters in the English alphabet and 26 = 2 * 13, the ROT13 function is its own inverse:

ROT13(ROT13(x)) = x for any basic Latin-alphabet text x

An example plaintext to ciphertext using ROT13:

Plain: chiodo
Cipher: puvbqb

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Polybius Square

A Polybius Square is a table that allows someone to translate letters into numbers. To give a small level of encryption, this table can be randomized and shared with the recipient. In order to fit the 26 letters of the alphabet into the 25 spots created by the table, the letters i and j are usually combined.
1 2 3 4 5
1 A B C D E
2 F G H I/J K
3 L M N O P
4 Q R S T U
5 V W X Y Z

Basic Form:
Plain: chiodo
Cipher: 313242434143

Extended Methods:
Method #1

Plaintext: chiodo
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
c h i o d o 
3 3 4 4 4 4 
1 2 2 3 1 3 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: chiodo
Cipher: nttfml

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Method #3

Plaintext: chiodo
method variations:
lrrsqn rrsqnl rsqnlr
sqnlrr qnlrrs nlrrsq

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Permutation Cipher
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 and the letters within that segment are permuted according to this key.
In theory, any transposition cipher can be viewed as a permutation cipher where E is equal to the length of the plaintext; this is too cumbersome a generalisation to use in actual practice, however.
The idea behind a permutation cipher is to keep the plaintext characters unchanged, butalter their positions by rearrangement using a permutation
This cipher is defined as:
Let m be a positive integer, and K consist of all permutations of {1,...,m}
For a key (permutation) , define:
The encryption function
The decryption function
A small example, assuming m = 6, and the key is the permutation :

The first row is the value of i, and the second row is the corresponding value of (i)
The inverse permutation, is constructed by interchanging the two rows, andrearranging the columns so that the first row is in increasing order, Therefore, is:

Total variation formula:

e = 2,718281828 , n - plaintext length

Plaintext: chiodo

all 720 cipher variations:
chiodo chiood chidoo chidoo chiodo chiood choido choiod chodio chodoi choodi
chooid chdoio chdooi chdioo chdioo chdoio chdooi choodi chooid chodoi chodio
choido choiod cihodo cihood cihdoo cihdoo cihodo cihood ciohdo ciohod ciodho
ciodoh cioodh cioohd cidoho cidooh cidhoo cidhoo cidoho cidooh cioodh cioohd
ciodoh ciodho ciohdo ciohod coihdo coihod coidho coidoh coiodh coiohd cohido
cohiod cohdio cohdoi cohodi cohoid codhio codhoi codiho codioh codoih codohi
coohdi coohid coodhi coodih cooidh cooihd cdioho cdiooh cdihoo cdihoo cdioho
cdiooh cdoiho cdoioh cdohio cdohoi cdoohi cdooih cdhoio cdhooi cdhioo cdhioo
cdhoio cdhooi cdoohi cdooih cdohoi cdohio cdoiho cdoioh coiodh coiohd coidoh
coidho coihdo coihod cooidh cooihd coodih coodhi coohdi coohid codoih codohi
codioh codiho codhio codhoi cohodi cohoid cohdoi cohdio cohido cohiod hciodo
hciood hcidoo hcidoo hciodo hciood hcoido hcoiod hcodio hcodoi hcoodi hcooid
hcdoio hcdooi hcdioo hcdioo hcdoio hcdooi hcoodi hcooid hcodoi hcodio hcoido
hcoiod hicodo hicood hicdoo hicdoo hicodo hicood hiocdo hiocod hiodco hiodoc
hioodc hioocd hidoco hidooc hidcoo hidcoo hidoco hidooc hioodc hioocd hiodoc
hiodco hiocdo hiocod hoicdo hoicod hoidco hoidoc hoiodc hoiocd hocido hociod
hocdio hocdoi hocodi hocoid hodcio hodcoi hodico hodioc hodoic hodoci hoocdi
hoocid hoodci hoodic hooidc hooicd hdioco hdiooc hdicoo hdicoo hdioco hdiooc
hdoico hdoioc hdocio hdocoi hdooci hdooic hdcoio hdcooi hdcioo hdcioo hdcoio
hdcooi hdooci hdooic hdocoi hdocio hdoico hdoioc hoiodc hoiocd hoidoc hoidco
hoicdo hoicod hooidc hooicd hoodic hoodci hoocdi hoocid hodoic hodoci hodioc
hodico hodcio hodcoi hocodi hocoid hocdoi hocdio hocido hociod ihcodo ihcood
ihcdoo ihcdoo ihcodo ihcood ihocdo ihocod ihodco ihodoc ihoodc ihoocd ihdoco
ihdooc ihdcoo ihdcoo ihdoco ihdooc ihoodc ihoocd ihodoc ihodco ihocdo ihocod
ichodo ichood ichdoo ichdoo ichodo ichood icohdo icohod icodho icodoh icoodh
icoohd icdoho icdooh icdhoo icdhoo icdoho icdooh icoodh icoohd icodoh icodho
icohdo icohod iochdo iochod iocdho iocdoh iocodh iocohd iohcdo iohcod iohdco
iohdoc iohodc iohocd iodhco iodhoc iodcho iodcoh iodoch iodohc ioohdc ioohcd
ioodhc ioodch ioocdh ioochd idcoho idcooh idchoo idchoo idcoho idcooh idocho
idocoh idohco idohoc idoohc idooch idhoco idhooc idhcoo idhcoo idhoco idhooc
idoohc idooch idohoc idohco idocho idocoh iocodh iocohd iocdoh iocdho iochdo
iochod ioocdh ioochd ioodch ioodhc ioohdc ioohcd iodoch iodohc iodcoh iodcho
iodhco iodhoc iohodc iohocd iohdoc iohdco iohcdo iohcod ohicdo ohicod ohidco
ohidoc ohiodc ohiocd ohcido ohciod ohcdio ohcdoi ohcodi ohcoid ohdcio ohdcoi
ohdico ohdioc ohdoic ohdoci ohocdi ohocid ohodci ohodic ohoidc ohoicd oihcdo
oihcod oihdco oihdoc oihodc oihocd oichdo oichod oicdho oicdoh oicodh oicohd
oidcho oidcoh oidhco oidhoc oidohc oidoch oiocdh oiochd oiodch oiodhc oiohdc
oiohcd ocihdo ocihod ocidho ocidoh ociodh ociohd ochido ochiod ochdio ochdoi
ochodi ochoid ocdhio ocdhoi ocdiho ocdioh ocdoih ocdohi ocohdi ocohid ocodhi
ocodih ocoidh ocoihd odicho odicoh odihco odihoc odiohc odioch odciho odcioh
odchio odchoi odcohi odcoih odhcio odhcoi odhico odhioc odhoic odhoci odochi
odocih odohci odohic odoihc odoich ooicdh ooichd ooidch ooidhc ooihdc ooihcd
oocidh oocihd oocdih oocdhi oochdi oochid oodcih oodchi oodich oodihc oodhic
oodhci oohcdi oohcid oohdci oohdic oohidc oohicd dhioco dhiooc dhicoo dhicoo
dhioco dhiooc dhoico dhoioc dhocio dhocoi dhooci dhooic dhcoio dhcooi dhcioo
dhcioo dhcoio dhcooi dhooci dhooic dhocoi dhocio dhoico dhoioc dihoco dihooc
dihcoo dihcoo dihoco dihooc diohco diohoc diocho diocoh diooch dioohc dicoho
dicooh dichoo dichoo dicoho dicooh diooch dioohc diocoh diocho diohco diohoc
doihco doihoc doicho doicoh doioch doiohc dohico dohioc dohcio dohcoi dohoci
dohoic dochio dochoi dociho docioh docoih docohi doohci doohic doochi doocih
dooich dooihc dcioho dciooh dcihoo dcihoo dcioho dciooh dcoiho dcoioh dcohio
dcohoi dcoohi dcooih dchoio dchooi dchioo dchioo dchoio dchooi dcoohi dcooih
dcohoi dcohio dcoiho dcoioh doioch doiohc doicoh doicho doihco doihoc dooich
dooihc doocih doochi doohci doohic docoih docohi docioh dociho dochio dochoi
dohoci dohoic dohcoi dohcio dohico dohioc ohiodc ohiocd ohidoc ohidco ohicdo
ohicod ohoidc ohoicd ohodic ohodci ohocdi ohocid ohdoic ohdoci ohdioc ohdico
ohdcio ohdcoi ohcodi ohcoid ohcdoi ohcdio ohcido ohciod oihodc oihocd oihdoc
oihdco oihcdo oihcod oiohdc oiohcd oiodhc oiodch oiocdh oiochd oidohc oidoch
oidhoc oidhco oidcho oidcoh oicodh oicohd oicdoh oicdho oichdo oichod ooihdc
ooihcd ooidhc ooidch ooicdh ooichd oohidc oohicd oohdic oohdci oohcdi oohcid
oodhic oodhci oodihc oodich oodcih oodchi oochdi oochid oocdhi oocdih oocidh
oocihd odiohc odioch odihoc odihco odicho odicoh odoihc odoich odohic odohci
odochi odocih odhoic odhoci odhioc odhico odhcio odhcoi odcohi odcoih odchoi
odchio odciho odcioh ociodh ociohd ocidoh ocidho ocihdo ocihod ocoidh ocoihd
ocodih ocodhi ocohdi ocohid ocdoih ocdohi ocdioh ocdiho ocdhio ocdhoi ochodi
ochoid ochdoi ochdio ochido ochiod

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History of cryptography
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