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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: voters
cipher variations:
wpufst xqvgtu yrwhuv zsxivw atyjwx
buzkxy cvalyz dwbmza excnab fydobc
gzepcd hafqde ibgref jchsfg kditgh
lejuhi mfkvij nglwjk ohmxkl pinylm
qjozmn rkpano slqbop tmrcpq unsdqr

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: voters
Cipher: elgvih

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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: voters

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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: voters
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: voters
Cipher: ibgref

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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: voters
Cipher: 154344512434

Extended Methods:
Method #1

Plaintext: voters
method variations:

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

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Method #3

Plaintext: voters
method variations:
usyfod syfodu yfodus
fodusy odusyf dusyfo

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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: voters

all 720 cipher variations:
voters votesr votres votrse votsre votser voetrs voetsr voerts voerst voesrt
voestr vorets vorest vortes vortse vorste vorset vosert vosetr vosret vosrte
vostre voster vtoers vtoesr vtores vtorse vtosre vtoser vteors vteosr vteros
vterso vtesro vtesor vtreos vtreso vtroes vtrose vtrsoe vtrseo vtsero vtseor
vtsreo vtsroe vtsore vtsoer vetors vetosr vetros vetrso vetsro vetsor veotrs
veotsr veorts veorst veosrt veostr verots verost vertos vertso versto versot
vesort vesotr vesrot vesrto vestro vestor vrteos vrteso vrtoes vrtose vrtsoe
vrtseo vretos vretso vreots vreost vresot vresto vroets vroest vrotes vrotse
vroste vroset vrseot vrseto vrsoet vrsote vrstoe vrsteo vstero vsteor vstreo
vstroe vstore vstoer vsetro vsetor vserto vserot vseort vseotr vsreto vsreot
vsrteo vsrtoe vsrote vsroet vsoert vsoetr vsoret vsorte vsotre vsoter ovters
ovtesr ovtres ovtrse ovtsre ovtser ovetrs ovetsr overts overst ovesrt ovestr
ovrets ovrest ovrtes ovrtse ovrste ovrset ovsert ovsetr ovsret ovsrte ovstre
ovster otvers otvesr otvres otvrse otvsre otvser otevrs otevsr otervs otersv
otesrv otesvr otrevs otresv otrves otrvse otrsve otrsev otserv otsevr otsrev
otsrve otsvre otsver oetvrs oetvsr oetrvs oetrsv oetsrv oetsvr oevtrs oevtsr
oevrts oevrst oevsrt oevstr oervts oervst oertvs oertsv oerstv oersvt oesvrt
oesvtr oesrvt oesrtv oestrv oestvr ortevs ortesv ortves ortvse ortsve ortsev
oretvs oretsv orevts orevst oresvt orestv orvets orvest orvtes orvtse orvste
orvset orsevt orsetv orsvet orsvte orstve orstev osterv ostevr ostrev ostrve
ostvre ostver osetrv osetvr osertv oservt osevrt osevtr osretv osrevt osrtev
osrtve osrvte osrvet osvert osvetr osvret osvrte osvtre osvter tovers tovesr
tovres tovrse tovsre tovser toevrs toevsr toervs toersv toesrv toesvr torevs
toresv torves torvse torsve torsev toserv tosevr tosrev tosrve tosvre tosver
tvoers tvoesr tvores tvorse tvosre tvoser tveors tveosr tveros tverso tvesro
tvesor tvreos tvreso tvroes tvrose tvrsoe tvrseo tvsero tvseor tvsreo tvsroe
tvsore tvsoer tevors tevosr tevros tevrso tevsro tevsor teovrs teovsr teorvs
teorsv teosrv teosvr terovs terosv tervos tervso tersvo tersov tesorv tesovr
tesrov tesrvo tesvro tesvor trveos trveso trvoes trvose trvsoe trvseo trevos
trevso treovs treosv tresov tresvo troevs troesv troves trovse trosve trosev
trseov trsevo trsoev trsove trsvoe trsveo tsvero tsveor tsvreo tsvroe tsvore
tsvoer tsevro tsevor tservo tserov tseorv tseovr tsrevo tsreov tsrveo tsrvoe
tsrove tsroev tsoerv tsoevr tsorev tsorve tsovre tsover eotvrs eotvsr eotrvs
eotrsv eotsrv eotsvr eovtrs eovtsr eovrts eovrst eovsrt eovstr eorvts eorvst
eortvs eortsv eorstv eorsvt eosvrt eosvtr eosrvt eosrtv eostrv eostvr etovrs
etovsr etorvs etorsv etosrv etosvr etvors etvosr etvros etvrso etvsro etvsor
etrvos etrvso etrovs etrosv etrsov etrsvo etsvro etsvor etsrvo etsrov etsorv
etsovr evtors evtosr evtros evtrso evtsro evtsor evotrs evotsr evorts evorst
evosrt evostr evrots evrost evrtos evrtso evrsto evrsot evsort evsotr evsrot
evsrto evstro evstor ertvos ertvso ertovs ertosv ertsov ertsvo ervtos ervtso
ervots ervost ervsot ervsto erovts erovst erotvs erotsv erostv erosvt ersvot
ersvto ersovt ersotv erstov erstvo estvro estvor estrvo estrov estorv estovr
esvtro esvtor esvrto esvrot esvort esvotr esrvto esrvot esrtvo esrtov esrotv
esrovt esovrt esovtr esorvt esortv esotrv esotvr rotevs rotesv rotves rotvse
rotsve rotsev roetvs roetsv roevts roevst roesvt roestv rovets rovest rovtes
rovtse rovste rovset rosevt rosetv rosvet rosvte rostve rostev rtoevs rtoesv
rtoves rtovse rtosve rtosev rteovs rteosv rtevos rtevso rtesvo rtesov rtveos
rtveso rtvoes rtvose rtvsoe rtvseo rtsevo rtseov rtsveo rtsvoe rtsove rtsoev
retovs retosv retvos retvso retsvo retsov reotvs reotsv reovts reovst reosvt
reostv revots revost revtos revtso revsto revsot resovt resotv resvot resvto
restvo restov rvteos rvteso rvtoes rvtose rvtsoe rvtseo rvetos rvetso rveots
rveost rvesot rvesto rvoets rvoest rvotes rvotse rvoste rvoset rvseot rvseto
rvsoet rvsote rvstoe rvsteo rstevo rsteov rstveo rstvoe rstove rstoev rsetvo
rsetov rsevto rsevot rseovt rseotv rsveto rsveot rsvteo rsvtoe rsvote rsvoet
rsoevt rsoetv rsovet rsovte rsotve rsotev soterv sotevr sotrev sotrve sotvre
sotver soetrv soetvr soertv soervt soevrt soevtr soretv sorevt sortev sortve
sorvte sorvet sovert sovetr sovret sovrte sovtre sovter stoerv stoevr storev
storve stovre stover steorv steovr sterov stervo stevro stevor streov strevo
stroev strove strvoe strveo stvero stveor stvreo stvroe stvore stvoer setorv
setovr setrov setrvo setvro setvor seotrv seotvr seortv seorvt seovrt seovtr
serotv serovt sertov sertvo servto servot sevort sevotr sevrot sevrto sevtro
sevtor srteov srtevo srtoev srtove srtvoe srtveo sretov sretvo sreotv sreovt
srevot srevto sroetv sroevt srotev srotve srovte srovet srveot srveto srvoet
srvote srvtoe srvteo svtero svteor svtreo svtroe svtore svtoer svetro svetor
sverto sverot sveort sveotr svreto svreot svrteo svrtoe svrote svroet svoert
svoetr svoret svorte svotre svoter

Read more ...[1] , [2] , [3]

History of cryptography
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