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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: hances
cipher variations:
ibodft jcpegu kdqfhv lergiw mfshjx
ngtiky ohujlz pivkma qjwlnb rkxmoc
slynpd tmzoqe unaprf vobqsg wpcrth
xqdsui yretvj zsfuwk atgvxl buhwym
cvixzn dwjyao exkzbp fylacq gzmbdr

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: hances
Cipher: szmxvh

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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: hances

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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: hances
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: hances
Cipher: unaprf

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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: hances
Cipher: 321133315134

Extended Methods:
Method #1

Plaintext: hances
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
h a n c e s 
3 1 3 3 5 3 
2 1 3 1 1 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: hances
Cipher: cnpbcq

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Method #3

Plaintext: hances
method variations:
blnvlo lnvlob nvlobl
vlobln loblnv oblnvl

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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: hances

all 720 cipher variations:
hances hancse hanecs hanesc hansec hansce hacnes hacnse hacens hacesn hacsen
hacsne haecns haecsn haencs haensc haesnc haescn hascen hascne hasecn hasenc
hasnec hasnce hnaces hnacse hnaecs hnaesc hnasec hnasce hncaes hncase hnceas
hncesa hncsea hncsae hnecas hnecsa hneacs hneasc hnesac hnesca hnscea hnscae
hnseca hnseac hnsaec hnsace hcnaes hcnase hcneas hcnesa hcnsea hcnsae hcanes
hcanse hcaens hcaesn hcasen hcasne hceans hceasn hcenas hcensa hcesna hcesan
hcsaen hcsane hcsean hcsena hcsnea hcsnae hencas hencsa henacs henasc hensac
hensca hecnas hecnsa hecans hecasn hecsan hecsna heacns heacsn heancs heansc
heasnc heascn hescan hescna hesacn hesanc hesnac hesnca hsncea hsncae hsneca
hsneac hsnaec hsnace hscnea hscnae hscena hscean hscaen hscane hsecna hsecan
hsenca hsenac hseanc hseacn hsacen hsacne hsaecn hsaenc hsanec hsance ahnces
ahncse ahnecs ahnesc ahnsec ahnsce ahcnes ahcnse ahcens ahcesn ahcsen ahcsne
ahecns ahecsn ahencs ahensc ahesnc ahescn ahscen ahscne ahsecn ahsenc ahsnec
ahsnce anhces anhcse anhecs anhesc anhsec anhsce anches anchse ancehs ancesh
ancseh ancshe anechs anecsh anehcs anehsc aneshc anesch ansceh ansche ansech
ansehc anshec anshce acnhes acnhse acnehs acnesh acnseh acnshe achnes achnse
achens achesn achsen achsne acehns acehsn acenhs acensh acesnh aceshn acshen
acshne acsehn acsenh acsneh acsnhe aenchs aencsh aenhcs aenhsc aenshc aensch
aecnhs aecnsh aechns aechsn aecshn aecsnh aehcns aehcsn aehncs aehnsc aehsnc
aehscn aeschn aescnh aeshcn aeshnc aesnhc aesnch asnceh asnche asnech asnehc
asnhec asnhce ascneh ascnhe ascenh ascehn aschen aschne asecnh asechn asench
asenhc asehnc asehcn ashcen ashcne ashecn ashenc ashnec ashnce nahces nahcse
nahecs nahesc nahsec nahsce naches nachse nacehs nacesh nacseh nacshe naechs
naecsh naehcs naehsc naeshc naesch nasceh nasche nasech nasehc nashec nashce
nhaces nhacse nhaecs nhaesc nhasec nhasce nhcaes nhcase nhceas nhcesa nhcsea
nhcsae nhecas nhecsa nheacs nheasc nhesac nhesca nhscea nhscae nhseca nhseac
nhsaec nhsace nchaes nchase ncheas nchesa nchsea nchsae ncahes ncahse ncaehs
ncaesh ncaseh ncashe nceahs nceash ncehas ncehsa ncesha ncesah ncsaeh ncsahe
ncseah ncseha ncshea ncshae nehcas nehcsa nehacs nehasc nehsac nehsca nechas
nechsa necahs necash necsah necsha neachs neacsh neahcs neahsc neashc neasch
nescah nescha nesach nesahc neshac neshca nshcea nshcae nsheca nsheac nshaec
nshace nschea nschae nsceha nsceah nscaeh nscahe nsecha nsecah nsehca nsehac
nseahc nseach nsaceh nsache nsaech nsaehc nsahec nsahce canhes canhse canehs
canesh canseh canshe cahnes cahnse cahens cahesn cahsen cahsne caehns caehsn
caenhs caensh caesnh caeshn cashen cashne casehn casenh casneh casnhe cnahes
cnahse cnaehs cnaesh cnaseh cnashe cnhaes cnhase cnheas cnhesa cnhsea cnhsae
cnehas cnehsa cneahs cneash cnesah cnesha cnshea cnshae cnseha cnseah cnsaeh
cnsahe chnaes chnase chneas chnesa chnsea chnsae chanes chanse chaens chaesn
chasen chasne cheans cheasn chenas chensa chesna chesan chsaen chsane chsean
chsena chsnea chsnae cenhas cenhsa cenahs cenash censah censha cehnas cehnsa
cehans cehasn cehsan cehsna ceahns ceahsn ceanhs ceansh ceasnh ceashn ceshan
ceshna cesahn cesanh cesnah cesnha csnhea csnhae csneha csneah csnaeh csnahe
cshnea cshnae cshena cshean cshaen cshane csehna csehan csenha csenah cseanh
cseahn csahen csahne csaehn csaenh csaneh csanhe eanchs eancsh eanhcs eanhsc
eanshc eansch eacnhs eacnsh eachns eachsn eacshn eacsnh eahcns eahcsn eahncs
eahnsc eahsnc eahscn easchn eascnh eashcn eashnc easnhc easnch enachs enacsh
enahcs enahsc enashc enasch encahs encash enchas enchsa encsha encsah enhcas
enhcsa enhacs enhasc enhsac enhsca enscha enscah enshca enshac ensahc ensach
ecnahs ecnash ecnhas ecnhsa ecnsha ecnsah ecanhs ecansh ecahns ecahsn ecashn
ecasnh echans echasn echnas echnsa echsna echsan ecsahn ecsanh ecshan ecshna
ecsnha ecsnah ehncas ehncsa ehnacs ehnasc ehnsac ehnsca ehcnas ehcnsa ehcans
ehcasn ehcsan ehcsna ehacns ehacsn ehancs ehansc ehasnc ehascn ehscan ehscna
ehsacn ehsanc ehsnac ehsnca esncha esncah esnhca esnhac esnahc esnach escnha
escnah eschna eschan escahn escanh eshcna eshcan eshnca eshnac eshanc eshacn
esachn esacnh esahcn esahnc esanhc esanch sanceh sanche sanech sanehc sanhec
sanhce sacneh sacnhe sacenh sacehn sachen sachne saecnh saechn saench saenhc
saehnc saehcn sahcen sahcne sahecn sahenc sahnec sahnce snaceh snache snaech
snaehc snahec snahce sncaeh sncahe snceah snceha snchea snchae snecah snecha
sneach sneahc snehac snehca snhcea snhcae snheca snheac snhaec snhace scnaeh
scnahe scneah scneha scnhea scnhae scaneh scanhe scaenh scaehn scahen scahne
sceanh sceahn scenah scenha scehna scehan schaen schane schean schena schnea
schnae sencah sencha senach senahc senhac senhca secnah secnha secanh secahn
sechan sechna seacnh seachn seanch seanhc seahnc seahcn sehcan sehcna sehacn
sehanc sehnac sehnca shncea shncae shneca shneac shnaec shnace shcnea shcnae
shcena shcean shcaen shcane shecna shecan shenca shenac sheanc sheacn shacen
shacne shaecn shaenc shanec shance

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History of cryptography
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