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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: moesch
cipher variations:
npftdi oqguej prhvfk qsiwgl rtjxhm
sukyin tvlzjo uwmakp vxnblq wyocmr
xzpdns yaqeot zbrfpu acsgqv bdthrw
ceuisx dfvjty egwkuz fhxlva giymwb
hjznxc ikaoyd jlbpze kmcqaf lndrbg

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: moesch
Cipher: nlvhxs

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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: moesch

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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: moesch
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: moesch
Cipher: zbrfpu

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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: moesch
Cipher: 234351343132

Extended Methods:
Method #1

Plaintext: moesch
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
m o e s c h 
2 4 5 3 3 3 
3 3 1 4 1 2 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: moesch
Cipher: rpnnqf

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Method #3

Plaintext: moesch
method variations:
sxlolg xlolgs lolgsx
olgsxl lgsxlo gsxlol

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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: moesch

all 720 cipher variations:
moesch moeshc moecsh moechs moehcs moehsc mosech mosehc mosceh mosche moshce
moshec mocseh mocshe mocesh mocehs moches mochse mohsce mohsec mohcse mohces
mohecs mohesc meosch meoshc meocsh meochs meohcs meohsc mesoch mesohc mescoh
mescho meshco meshoc mecsoh mecsho mecosh mecohs mechos mechso mehsco mehsoc
mehcso mehcos mehocs mehosc mseoch mseohc msecoh msecho msehco msehoc msoech
msoehc msoceh msoche msohce msohec mscoeh mscohe msceoh msceho mscheo mschoe
mshoce mshoec mshcoe mshceo msheco msheoc mcesoh mcesho mceosh mceohs mcehos
mcehso mcseoh mcseho mcsoeh mcsohe mcshoe mcsheo mcoseh mcoshe mcoesh mcoehs
mcohes mcohse mchsoe mchseo mchose mchoes mcheos mcheso mhesco mhesoc mhecso
mhecos mheocs mheosc mhseco mhseoc mhsceo mhscoe mhsoce mhsoec mhcseo mhcsoe
mhceso mhceos mhcoes mhcose mhosce mhosec mhocse mhoces mhoecs mhoesc omesch
omeshc omecsh omechs omehcs omehsc omsech omsehc omsceh omsche omshce omshec
omcseh omcshe omcesh omcehs omches omchse omhsce omhsec omhcse omhces omhecs
omhesc oemsch oemshc oemcsh oemchs oemhcs oemhsc oesmch oesmhc oescmh oeschm
oeshcm oeshmc oecsmh oecshm oecmsh oecmhs oechms oechsm oehscm oehsmc oehcsm
oehcms oehmcs oehmsc osemch osemhc osecmh osechm osehcm osehmc osmech osmehc
osmceh osmche osmhce osmhec oscmeh oscmhe oscemh oscehm oschem oschme oshmce
oshmec oshcme oshcem oshecm oshemc ocesmh oceshm ocemsh ocemhs ocehms ocehsm
ocsemh ocsehm ocsmeh ocsmhe ocshme ocshem ocmseh ocmshe ocmesh ocmehs ocmhes
ocmhse ochsme ochsem ochmse ochmes ochems ochesm ohescm ohesmc ohecsm ohecms
ohemcs ohemsc ohsecm ohsemc ohscem ohscme ohsmce ohsmec ohcsem ohcsme ohcesm
ohcems ohcmes ohcmse ohmsce ohmsec ohmcse ohmces ohmecs ohmesc eomsch eomshc
eomcsh eomchs eomhcs eomhsc eosmch eosmhc eoscmh eoschm eoshcm eoshmc eocsmh
eocshm eocmsh eocmhs eochms eochsm eohscm eohsmc eohcsm eohcms eohmcs eohmsc
emosch emoshc emocsh emochs emohcs emohsc emsoch emsohc emscoh emscho emshco
emshoc emcsoh emcsho emcosh emcohs emchos emchso emhsco emhsoc emhcso emhcos
emhocs emhosc esmoch esmohc esmcoh esmcho esmhco esmhoc esomch esomhc esocmh
esochm esohcm esohmc escomh escohm escmoh escmho eschmo eschom eshocm eshomc
eshcom eshcmo eshmco eshmoc ecmsoh ecmsho ecmosh ecmohs ecmhos ecmhso ecsmoh
ecsmho ecsomh ecsohm ecshom ecshmo ecosmh ecoshm ecomsh ecomhs ecohms ecohsm
echsom echsmo echosm echoms echmos echmso ehmsco ehmsoc ehmcso ehmcos ehmocs
ehmosc ehsmco ehsmoc ehscmo ehscom ehsocm ehsomc ehcsmo ehcsom ehcmso ehcmos
ehcoms ehcosm ehoscm ehosmc ehocsm ehocms ehomcs ehomsc soemch soemhc soecmh
soechm soehcm soehmc somech somehc somceh somche somhce somhec socmeh socmhe
socemh socehm sochem sochme sohmce sohmec sohcme sohcem sohecm sohemc seomch
seomhc seocmh seochm seohcm seohmc semoch semohc semcoh semcho semhco semhoc
secmoh secmho secomh secohm sechom sechmo sehmco sehmoc sehcmo sehcom sehocm
sehomc smeoch smeohc smecoh smecho smehco smehoc smoech smoehc smoceh smoche
smohce smohec smcoeh smcohe smceoh smceho smcheo smchoe smhoce smhoec smhcoe
smhceo smheco smheoc scemoh scemho sceomh sceohm scehom scehmo scmeoh scmeho
scmoeh scmohe scmhoe scmheo scomeh scomhe scoemh scoehm scohem scohme schmoe
schmeo schome schoem scheom schemo shemco shemoc shecmo shecom sheocm sheomc
shmeco shmeoc shmceo shmcoe shmoce shmoec shcmeo shcmoe shcemo shceom shcoem
shcome shomce shomec shocme shocem shoecm shoemc coesmh coeshm coemsh coemhs
coehms coehsm cosemh cosehm cosmeh cosmhe coshme coshem comseh comshe comesh
comehs comhes comhse cohsme cohsem cohmse cohmes cohems cohesm ceosmh ceoshm
ceomsh ceomhs ceohms ceohsm cesomh cesohm cesmoh cesmho ceshmo ceshom cemsoh
cemsho cemosh cemohs cemhos cemhso cehsmo cehsom cehmso cehmos cehoms cehosm
cseomh cseohm csemoh csemho csehmo csehom csoemh csoehm csomeh csomhe csohme
csohem csmoeh csmohe csmeoh csmeho csmheo csmhoe cshome cshoem cshmoe cshmeo
cshemo csheom cmesoh cmesho cmeosh cmeohs cmehos cmehso cmseoh cmseho cmsoeh
cmsohe cmshoe cmsheo cmoseh cmoshe cmoesh cmoehs cmohes cmohse cmhsoe cmhseo
cmhose cmhoes cmheos cmheso chesmo chesom chemso chemos cheoms cheosm chsemo
chseom chsmeo chsmoe chsome chsoem chmseo chmsoe chmeso chmeos chmoes chmose
chosme chosem chomse chomes choems choesm hoescm hoesmc hoecsm hoecms hoemcs
hoemsc hosecm hosemc hoscem hoscme hosmce hosmec hocsem hocsme hocesm hocems
hocmes hocmse homsce homsec homcse homces homecs homesc heoscm heosmc heocsm
heocms heomcs heomsc hesocm hesomc hescom hescmo hesmco hesmoc hecsom hecsmo
hecosm hecoms hecmos hecmso hemsco hemsoc hemcso hemcos hemocs hemosc hseocm
hseomc hsecom hsecmo hsemco hsemoc hsoecm hsoemc hsocem hsocme hsomce hsomec
hscoem hscome hsceom hscemo hscmeo hscmoe hsmoce hsmoec hsmcoe hsmceo hsmeco
hsmeoc hcesom hcesmo hceosm hceoms hcemos hcemso hcseom hcsemo hcsoem hcsome
hcsmoe hcsmeo hcosem hcosme hcoesm hcoems hcomes hcomse hcmsoe hcmseo hcmose
hcmoes hcmeos hcmeso hmesco hmesoc hmecso hmecos hmeocs hmeosc hmseco hmseoc
hmsceo hmscoe hmsoce hmsoec hmcseo hmcsoe hmceso hmceos hmcoes hmcose hmosce
hmosec hmocse hmoces hmoecs hmoesc

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History of cryptography
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