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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: zoster
cipher variations:
aptufs bquvgt crvwhu dswxiv etxyjw
fuyzkx gvzaly hwabmz ixbcna jycdob
kzdepc laefqd mbfgre ncghsf odhitg
peijuh qfjkvi rgklwj shlmxk timnyl
ujnozm vkopan wlpqbo xmqrcp ynrsdq

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: zoster
Cipher: alhgvi

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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: zoster

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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: zoster
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: zoster
Cipher: mbfgre

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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: zoster
Cipher: 554334445124

Extended Methods:
Method #1

Plaintext: zoster
method variations:

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

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Method #3

Plaintext: zoster
method variations:
untyfy ntyfyu tyfyun
yfyunt fyunty yuntyf

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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: zoster

all 720 cipher variations:
zoster zostre zosetr zosert zosret zosrte zotser zotsre zotesr zoters zotres
zotrse zoetsr zoetrs zoestr zoesrt zoerst zoerts zortes zortse zorets zorest
zorset zorste zsoter zsotre zsoetr zsoert zsoret zsorte zstoer zstore zsteor
zstero zstreo zstroe zsetor zsetro zseotr zseort zserot zserto zsrteo zsrtoe
zsreto zsreot zsroet zsrote ztsoer ztsore ztseor ztsero ztsreo ztsroe ztoser
ztosre ztoesr ztoers ztores ztorse zteosr zteors ztesor ztesro zterso zteros
ztroes ztrose ztreos ztreso ztrseo ztrsoe zestor zestro zesotr zesort zesrot
zesrto zetsor zetsro zetosr zetors zetros zetrso zeotsr zeotrs zeostr zeosrt
zeorst zeorts zertos zertso zerots zerost zersot zersto zrsteo zrstoe zrseto
zrseot zrsoet zrsote zrtseo zrtsoe zrteso zrteos zrtoes zrtose zretso zretos
zresto zresot zreost zreots zrotes zrotse zroets zroest zroset zroste ozster
ozstre ozsetr ozsert ozsret ozsrte oztser oztsre oztesr ozters oztres oztrse
ozetsr ozetrs ozestr ozesrt ozerst ozerts ozrtes ozrtse ozrets ozrest ozrset
ozrste oszter osztre oszetr oszert oszret oszrte ostzer ostzre ostezr osterz
ostrez ostrze osetzr osetrz oseztr osezrt oserzt osertz osrtez osrtze osretz
osrezt osrzet osrzte otszer otszre otsezr otserz otsrez otsrze otzser otzsre
otzesr otzers otzres otzrse otezsr otezrs oteszr otesrz otersz oterzs otrzes
otrzse otrezs otresz otrsez otrsze oestzr oestrz oesztr oeszrt oesrzt oesrtz
oetszr oetsrz oetzsr oetzrs oetrzs oetrsz oeztsr oeztrs oezstr oezsrt oezrst
oezrts oertzs oertsz oerzts oerzst oerszt oerstz orstez orstze orsetz orsezt
orszet orszte ortsez ortsze ortesz ortezs ortzes ortzse oretsz oretzs orestz
oreszt orezst orezts orztes orztse orzets orzest orzset orzste sozter soztre
sozetr sozert sozret sozrte sotzer sotzre sotezr soterz sotrez sotrze soetzr
soetrz soeztr soezrt soerzt soertz sortez sortze soretz sorezt sorzet sorzte
szoter szotre szoetr szoert szoret szorte sztoer sztore szteor sztero sztreo
sztroe szetor szetro szeotr szeort szerot szerto szrteo szrtoe szreto szreot
szroet szrote stzoer stzore stzeor stzero stzreo stzroe stozer stozre stoezr
stoerz storez storze steozr steorz stezor stezro sterzo steroz stroez stroze
streoz strezo strzeo strzoe seztor seztro sezotr sezort sezrot sezrto setzor
setzro setozr setorz setroz setrzo seotzr seotrz seoztr seozrt seorzt seortz
sertoz sertzo serotz serozt serzot serzto srzteo srztoe srzeto srzeot srzoet
srzote srtzeo srtzoe srtezo srteoz srtoez srtoze sretzo sretoz srezto srezot
sreozt sreotz srotez srotze sroetz sroezt srozet srozte toszer toszre tosezr
toserz tosrez tosrze tozser tozsre tozesr tozers tozres tozrse toezsr toezrs
toeszr toesrz toersz toerzs torzes torzse torezs toresz torsez torsze tsozer
tsozre tsoezr tsoerz tsorez tsorze tszoer tszore tszeor tszero tszreo tszroe
tsezor tsezro tseozr tseorz tseroz tserzo tsrzeo tsrzoe tsrezo tsreoz tsroez
tsroze tzsoer tzsore tzseor tzsero tzsreo tzsroe tzoser tzosre tzoesr tzoers
tzores tzorse tzeosr tzeors tzesor tzesro tzerso tzeros tzroes tzrose tzreos
tzreso tzrseo tzrsoe teszor teszro tesozr tesorz tesroz tesrzo tezsor tezsro
tezosr tezors tezros tezrso teozsr teozrs teoszr teosrz teorsz teorzs terzos
terzso terozs terosz tersoz terszo trszeo trszoe trsezo trseoz trsoez trsoze
trzseo trzsoe trzeso trzeos trzoes trzose trezso trezos treszo tresoz treosz
treozs trozes trozse troezs troesz trosez trosze eostzr eostrz eosztr eoszrt
eosrzt eosrtz eotszr eotsrz eotzsr eotzrs eotrzs eotrsz eoztsr eoztrs eozstr
eozsrt eozrst eozrts eortzs eortsz eorzts eorzst eorszt eorstz esotzr esotrz
esoztr esozrt esorzt esortz estozr estorz estzor estzro estrzo estroz esztor
esztro eszotr eszort eszrot eszrto esrtzo esrtoz esrzto esrzot esrozt esrotz
etsozr etsorz etszor etszro etsrzo etsroz etoszr etosrz etozsr etozrs etorzs
etorsz etzosr etzors etzsor etzsro etzrso etzros etrozs etrosz etrzos etrzso
etrszo etrsoz ezstor ezstro ezsotr ezsort ezsrot ezsrto eztsor eztsro eztosr
eztors eztros eztrso ezotsr ezotrs ezostr ezosrt ezorst ezorts ezrtos ezrtso
ezrots ezrost ezrsot ezrsto erstzo erstoz erszto erszot ersozt ersotz ertszo
ertsoz ertzso ertzos ertozs ertosz erztso erztos erzsto erzsot erzost erzots
erotzs erotsz erozts erozst eroszt erostz rostez rostze rosetz rosezt roszet
roszte rotsez rotsze rotesz rotezs rotzes rotzse roetsz roetzs roestz roeszt
roezst roezts roztes roztse rozets rozest rozset rozste rsotez rsotze rsoetz
rsoezt rsozet rsozte rstoez rstoze rsteoz rstezo rstzeo rstzoe rsetoz rsetzo
rseotz rseozt rsezot rsezto rszteo rsztoe rszeto rszeot rszoet rszote rtsoez
rtsoze rtseoz rtsezo rtszeo rtszoe rtosez rtosze rtoesz rtoezs rtozes rtozse
rteosz rteozs rtesoz rteszo rtezso rtezos rtzoes rtzose rtzeos rtzeso rtzseo
rtzsoe restoz restzo resotz resozt reszot reszto retsoz retszo retosz retozs
retzos retzso reotsz reotzs reostz reoszt reozst reozts reztos reztso rezots
rezost rezsot rezsto rzsteo rzstoe rzseto rzseot rzsoet rzsote rztseo rztsoe
rzteso rzteos rztoes rztose rzetso rzetos rzesto rzesot rzeost rzeots rzotes
rzotse rzoets rzoest rzoset rzoste

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History of cryptography
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