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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: wuster
cipher variations:
xvtufs ywuvgt zxvwhu aywxiv bzxyjw
cayzkx dbzaly ecabmz fdbcna gecdob
hfdepc igefqd jhfgre kighsf ljhitg
mkijuh nljkvi omklwj pnlmxk qomnyl
rpnozm sqopan trpqbo usqrcp vtrsdq

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: wuster
Cipher: dfhgvi

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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: wuster

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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: wuster
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: wuster
Cipher: jhfgre

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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: wuster
Cipher: 255434445124

Extended Methods:
Method #1

Plaintext: wuster
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
w u s t e r 
2 5 3 4 5 2 
5 4 4 4 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: wuster
Cipher: wskutq

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Method #3

Plaintext: wuster
method variations:
zotyfi otyfiz tyfizo
yfizot fizoty izotyf

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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: wuster

all 720 cipher variations:
wuster wustre wusetr wusert wusret wusrte wutser wutsre wutesr wuters wutres
wutrse wuetsr wuetrs wuestr wuesrt wuerst wuerts wurtes wurtse wurets wurest
wurset wurste wsuter wsutre wsuetr wsuert wsuret wsurte wstuer wsture wsteur
wsteru wstreu wstrue wsetur wsetru wseutr wseurt wserut wsertu wsrteu wsrtue
wsretu wsreut wsruet wsrute wtsuer wtsure wtseur wtseru wtsreu wtsrue wtuser
wtusre wtuesr wtuers wtures wturse wteusr wteurs wtesur wtesru wtersu wterus
wtrues wtruse wtreus wtresu wtrseu wtrsue westur westru wesutr wesurt wesrut
wesrtu wetsur wetsru wetusr weturs wetrus wetrsu weutsr weutrs weustr weusrt
weurst weurts wertus wertsu weruts werust wersut werstu wrsteu wrstue wrsetu
wrseut wrsuet wrsute wrtseu wrtsue wrtesu wrteus wrtues wrtuse wretsu wretus
wrestu wresut wreust wreuts wrutes wrutse wruets wruest wruset wruste uwster
uwstre uwsetr uwsert uwsret uwsrte uwtser uwtsre uwtesr uwters uwtres uwtrse
uwetsr uwetrs uwestr uwesrt uwerst uwerts uwrtes uwrtse uwrets uwrest uwrset
uwrste uswter uswtre uswetr uswert uswret uswrte ustwer ustwre ustewr usterw
ustrew ustrwe usetwr usetrw usewtr usewrt userwt usertw usrtew usrtwe usretw
usrewt usrwet usrwte utswer utswre utsewr utserw utsrew utsrwe utwser utwsre
utwesr utwers utwres utwrse utewsr utewrs uteswr utesrw utersw uterws utrwes
utrwse utrews utresw utrsew utrswe uestwr uestrw ueswtr ueswrt uesrwt uesrtw
uetswr uetsrw uetwsr uetwrs uetrws uetrsw uewtsr uewtrs uewstr uewsrt uewrst
uewrts uertws uertsw uerwts uerwst uerswt uerstw urstew urstwe ursetw ursewt
urswet urswte urtsew urtswe urtesw urtews urtwes urtwse uretsw uretws urestw
ureswt urewst urewts urwtes urwtse urwets urwest urwset urwste suwter suwtre
suwetr suwert suwret suwrte sutwer sutwre sutewr suterw sutrew sutrwe suetwr
suetrw suewtr suewrt suerwt suertw surtew surtwe suretw surewt surwet surwte
swuter swutre swuetr swuert swuret swurte swtuer swture swteur swteru swtreu
swtrue swetur swetru sweutr sweurt swerut swertu swrteu swrtue swretu swreut
swruet swrute stwuer stwure stweur stweru stwreu stwrue stuwer stuwre stuewr
stuerw sturew sturwe steuwr steurw stewur stewru sterwu steruw struew struwe
streuw strewu strweu strwue sewtur sewtru sewutr sewurt sewrut sewrtu setwur
setwru setuwr seturw setruw setrwu seutwr seutrw seuwtr seuwrt seurwt seurtw
sertuw sertwu serutw seruwt serwut serwtu srwteu srwtue srwetu srweut srwuet
srwute srtweu srtwue srtewu srteuw srtuew srtuwe sretwu sretuw srewtu srewut
sreuwt sreutw srutew srutwe sruetw sruewt sruwet sruwte tuswer tuswre tusewr
tuserw tusrew tusrwe tuwser tuwsre tuwesr tuwers tuwres tuwrse tuewsr tuewrs
tueswr tuesrw tuersw tuerws turwes turwse turews turesw tursew turswe tsuwer
tsuwre tsuewr tsuerw tsurew tsurwe tswuer tswure tsweur tsweru tswreu tswrue
tsewur tsewru tseuwr tseurw tseruw tserwu tsrweu tsrwue tsrewu tsreuw tsruew
tsruwe twsuer twsure twseur twseru twsreu twsrue twuser twusre twuesr twuers
twures twurse tweusr tweurs twesur twesru twersu twerus twrues twruse twreus
twresu twrseu twrsue teswur teswru tesuwr tesurw tesruw tesrwu tewsur tewsru
tewusr tewurs tewrus tewrsu teuwsr teuwrs teuswr teusrw teursw teurws terwus
terwsu teruws terusw tersuw terswu trsweu trswue trsewu trseuw trsuew trsuwe
trwseu trwsue trwesu trweus trwues trwuse trewsu trewus treswu tresuw treusw
treuws truwes truwse truews truesw trusew truswe eustwr eustrw euswtr euswrt
eusrwt eusrtw eutswr eutsrw eutwsr eutwrs eutrws eutrsw euwtsr euwtrs euwstr
euwsrt euwrst euwrts eurtws eurtsw eurwts eurwst eurswt eurstw esutwr esutrw
esuwtr esuwrt esurwt esurtw estuwr esturw estwur estwru estrwu estruw eswtur
eswtru eswutr eswurt eswrut eswrtu esrtwu esrtuw esrwtu esrwut esruwt esrutw
etsuwr etsurw etswur etswru etsrwu etsruw etuswr etusrw etuwsr etuwrs eturws
etursw etwusr etwurs etwsur etwsru etwrsu etwrus etruws etrusw etrwus etrwsu
etrswu etrsuw ewstur ewstru ewsutr ewsurt ewsrut ewsrtu ewtsur ewtsru ewtusr
ewturs ewtrus ewtrsu ewutsr ewutrs ewustr ewusrt ewurst ewurts ewrtus ewrtsu
ewruts ewrust ewrsut ewrstu erstwu erstuw erswtu erswut ersuwt ersutw ertswu
ertsuw ertwsu ertwus ertuws ertusw erwtsu erwtus erwstu erwsut erwust erwuts
erutws erutsw eruwts eruwst eruswt erustw rustew rustwe rusetw rusewt ruswet
ruswte rutsew rutswe rutesw rutews rutwes rutwse ruetsw ruetws ruestw rueswt
ruewst ruewts ruwtes ruwtse ruwets ruwest ruwset ruwste rsutew rsutwe rsuetw
rsuewt rsuwet rsuwte rstuew rstuwe rsteuw rstewu rstweu rstwue rsetuw rsetwu
rseutw rseuwt rsewut rsewtu rswteu rswtue rswetu rsweut rswuet rswute rtsuew
rtsuwe rtseuw rtsewu rtsweu rtswue rtusew rtuswe rtuesw rtuews rtuwes rtuwse
rteusw rteuws rtesuw rteswu rtewsu rtewus rtwues rtwuse rtweus rtwesu rtwseu
rtwsue restuw restwu resutw resuwt reswut reswtu retsuw retswu retusw retuws
retwus retwsu reutsw reutws reustw reuswt reuwst reuwts rewtus rewtsu rewuts
rewust rewsut rewstu rwsteu rwstue rwsetu rwseut rwsuet rwsute rwtseu rwtsue
rwtesu rwteus rwtues rwtuse rwetsu rwetus rwestu rwesut rweust rweuts rwutes
rwutse rwuets rwuest rwuset rwuste

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History of cryptography
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