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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: redtop
cipher variations:
sfeupq tgfvqr uhgwrs vihxst wjiytu
xkjzuv ylkavw zmlbwx anmcxy bondyz
cpoeza dqpfab erqgbc fsrhcd gtside
hutjef ivukfg jwvlgh kxwmhi lyxnij
mzyojk nazpkl obaqlm pcbrmn qdcsno

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: redtop
Cipher: ivwglk

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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: redtop

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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: redtop
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: redtop
Cipher: erqgbc

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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: redtop
Cipher: 245141444353

Extended Methods:
Method #1

Plaintext: redtop
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
r e d t o p 
2 5 4 4 4 5 
4 1 1 4 3 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: redtop
Cipher: wtydqn

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Method #3

Plaintext: redtop
method variations:
yqqtxh qqtxhy qtxhyq
txhyqq xhyqqt hyqqtx

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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: redtop

all 720 cipher variations:
redtop redtpo redotp redopt redpot redpto retdop retdpo retodp retopd retpod
retpdo reotdp reotpd reodtp reodpt reopdt reoptd reptod reptdo repotd repodt
repdot repdto rdetop rdetpo rdeotp rdeopt rdepot rdepto rdteop rdtepo rdtoep
rdtope rdtpoe rdtpeo rdotep rdotpe rdoetp rdoept rdopet rdopte rdptoe rdpteo
rdpote rdpoet rdpeot rdpeto rtdeop rtdepo rtdoep rtdope rtdpoe rtdpeo rtedop
rtedpo rteodp rteopd rtepod rtepdo rtoedp rtoepd rtodep rtodpe rtopde rtoped
rtpeod rtpedo rtpoed rtpode rtpdoe rtpdeo rodtep rodtpe rodetp rodept rodpet
rodpte rotdep rotdpe rotedp rotepd rotped rotpde roetdp roetpd roedtp roedpt
roepdt roeptd ropted roptde ropetd ropedt ropdet ropdte rpdtoe rpdteo rpdote
rpdoet rpdeot rpdeto rptdoe rptdeo rptode rptoed rpteod rptedo rpotde rpoted
rpodte rpodet rpoedt rpoetd rpetod rpetdo rpeotd rpeodt rpedot rpedto erdtop
erdtpo erdotp erdopt erdpot erdpto ertdop ertdpo ertodp ertopd ertpod ertpdo
erotdp erotpd erodtp erodpt eropdt eroptd erptod erptdo erpotd erpodt erpdot
erpdto edrtop edrtpo edrotp edropt edrpot edrpto edtrop edtrpo edtorp edtopr
edtpor edtpro edotrp edotpr edortp edorpt edoprt edoptr edptor edptro edpotr
edport edprot edprto etdrop etdrpo etdorp etdopr etdpor etdpro etrdop etrdpo
etrodp etropd etrpod etrpdo etordp etorpd etodrp etodpr etopdr etoprd etprod
etprdo etpord etpodr etpdor etpdro eodtrp eodtpr eodrtp eodrpt eodprt eodptr
eotdrp eotdpr eotrdp eotrpd eotprd eotpdr eortdp eortpd eordtp eordpt eorpdt
eorptd eoptrd eoptdr eoprtd eoprdt eopdrt eopdtr epdtor epdtro epdotr epdort
epdrot epdrto eptdor eptdro eptodr eptord eptrod eptrdo epotdr epotrd epodtr
epodrt epordt eportd eprtod eprtdo eprotd eprodt eprdot eprdto dertop dertpo
derotp deropt derpot derpto detrop detrpo detorp detopr detpor detpro deotrp
deotpr deortp deorpt deoprt deoptr deptor deptro depotr deport deprot deprto
dretop dretpo dreotp dreopt drepot drepto drteop drtepo drtoep drtope drtpoe
drtpeo drotep drotpe droetp droept dropet dropte drptoe drpteo drpote drpoet
drpeot drpeto dtreop dtrepo dtroep dtrope dtrpoe dtrpeo dterop dterpo dteorp
dteopr dtepor dtepro dtoerp dtoepr dtorep dtorpe dtopre dtoper dtpeor dtpero
dtpoer dtpore dtproe dtpreo dortep dortpe doretp dorept dorpet dorpte dotrep
dotrpe doterp dotepr dotper dotpre doetrp doetpr doertp doerpt doeprt doeptr
dopter doptre dopetr dopert dopret doprte dprtoe dprteo dprote dproet dpreot
dpreto dptroe dptreo dptore dptoer dpteor dptero dpotre dpoter dporte dporet
dpoert dpoetr dpetor dpetro dpeotr dpeort dperot dperto tedrop tedrpo tedorp
tedopr tedpor tedpro terdop terdpo terodp teropd terpod terpdo teordp teorpd
teodrp teodpr teopdr teoprd teprod teprdo tepord tepodr tepdor tepdro tderop
tderpo tdeorp tdeopr tdepor tdepro tdreop tdrepo tdroep tdrope tdrpoe tdrpeo
tdorep tdorpe tdoerp tdoepr tdoper tdopre tdproe tdpreo tdpore tdpoer tdpeor
tdpero trdeop trdepo trdoep trdope trdpoe trdpeo tredop tredpo treodp treopd
trepod trepdo troedp troepd trodep trodpe tropde troped trpeod trpedo trpoed
trpode trpdoe trpdeo todrep todrpe toderp todepr todper todpre tordep tordpe
toredp torepd torped torpde toerdp toerpd toedrp toedpr toepdr toeprd topred
toprde toperd topedr topder topdre tpdroe tpdreo tpdore tpdoer tpdeor tpdero
tprdoe tprdeo tprode tproed tpreod tpredo tporde tpored tpodre tpoder tpoedr
tpoerd tperod tperdo tpeord tpeodr tpedor tpedro oedtrp oedtpr oedrtp oedrpt
oedprt oedptr oetdrp oetdpr oetrdp oetrpd oetprd oetpdr oertdp oertpd oerdtp
oerdpt oerpdt oerptd oeptrd oeptdr oeprtd oeprdt oepdrt oepdtr odetrp odetpr
odertp oderpt odeprt odeptr odterp odtepr odtrep odtrpe odtpre odtper odrtep
odrtpe odretp odrept odrpet odrpte odptre odpter odprte odpret odpert odpetr
otderp otdepr otdrep otdrpe otdpre otdper otedrp otedpr oterdp oterpd oteprd
otepdr otredp otrepd otrdep otrdpe otrpde otrped otperd otpedr otpred otprde
otpdre otpder ordtep ordtpe ordetp ordept ordpet ordpte ortdep ortdpe ortedp
ortepd ortped ortpde oretdp oretpd oredtp oredpt orepdt oreptd orpted orptde
orpetd orpedt orpdet orpdte opdtre opdter opdrte opdret opdert opdetr optdre
optder optrde optred opterd optedr oprtde oprted oprdte oprdet opredt opretd
opetrd opetdr opertd operdt opedrt opedtr pedtor pedtro pedotr pedort pedrot
pedrto petdor petdro petodr petord petrod petrdo peotdr peotrd peodtr peodrt
peordt peortd pertod pertdo perotd perodt perdot perdto pdetor pdetro pdeotr
pdeort pderot pderto pdteor pdtero pdtoer pdtore pdtroe pdtreo pdoter pdotre
pdoetr pdoert pdoret pdorte pdrtoe pdrteo pdrote pdroet pdreot pdreto ptdeor
ptdero ptdoer ptdore ptdroe ptdreo ptedor ptedro pteodr pteord pterod pterdo
ptoedr ptoerd ptoder ptodre ptorde ptored ptreod ptredo ptroed ptrode ptrdoe
ptrdeo podter podtre podetr podert podret podrte potder potdre potedr poterd
potred potrde poetdr poetrd poedtr poedrt poerdt poertd ported portde poretd
poredt pordet pordte prdtoe prdteo prdote prdoet prdeot prdeto prtdoe prtdeo
prtode prtoed prteod prtedo protde proted prodte prodet proedt proetd pretod
pretdo preotd preodt predot predto

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History of cryptography
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