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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: sliney
cipher variations:
tmjofz unkpga volqhb wpmric xqnsjd
yrotke zspulf atqvmg burwnh cvsxoi
dwtypj exuzqk fyvarl gzwbsm haxctn
ibyduo jczevp kdafwq lebgxr mfchys
ngdizt ohejau pifkbv qjglcw rkhmdx

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: sliney
Cipher: hormvb

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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: sliney

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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: sliney
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: sliney
Cipher: fyvarl

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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: sliney
Cipher: 341342335145

Extended Methods:
Method #1

Plaintext: sliney
method variations:

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

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Method #3

Plaintext: sliney
method variations:
dsmxqp smxqpd mxqpds
xqpdsm qpdsmx pdsmxq

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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: sliney

all 720 cipher variations:
sliney slinye slieny slieyn sliyen sliyne slniey slniye slneiy slneyi slnyei
slnyie sleniy slenyi sleiny sleiyn sleyin sleyni slynei slynie slyeni slyein
slyien slyine silney silnye sileny sileyn silyen silyne sinley sinlye sinely
sineyl sinyel sinyle sienly sienyl sielny sielyn sieyln sieynl siynel siynle
siyenl siyeln siylen siylne sniley snilye sniely snieyl sniyel sniyle snliey
snliye snleiy snleyi snlyei snlyie sneliy snelyi sneily sneiyl sneyil sneyli
snylei snylie snyeli snyeil snyiel snyile seinly seinyl seilny seilyn seiyln
seiynl senily seniyl senliy senlyi senyli senyil selniy selnyi seliny seliyn
selyin selyni seynli seynil seylni seylin seyiln seyinl syinel syinle syienl
syieln syilen syilne syniel synile syneil syneli synlei synlie syenil syenli
syeinl syeiln syelin syelni sylnei sylnie syleni sylein sylien syline lsiney
lsinye lsieny lsieyn lsiyen lsiyne lsniey lsniye lsneiy lsneyi lsnyei lsnyie
lseniy lsenyi lseiny lseiyn lseyin lseyni lsynei lsynie lsyeni lsyein lsyien
lsyine lisney lisnye liseny liseyn lisyen lisyne linsey linsye linesy lineys
linyes linyse liensy lienys liesny liesyn lieysn lieyns liynes liynse liyens
liyesn liysen liysne lnisey lnisye lniesy lnieys lniyes lniyse lnsiey lnsiye
lnseiy lnseyi lnsyei lnsyie lnesiy lnesyi lneisy lneiys lneyis lneysi lnysei
lnysie lnyesi lnyeis lnyies lnyise leinsy leinys leisny leisyn leiysn leiyns
lenisy leniys lensiy lensyi lenysi lenyis lesniy lesnyi lesiny lesiyn lesyin
lesyni leynsi leynis leysni leysin leyisn leyins lyines lyinse lyiens lyiesn
lyisen lyisne lynies lynise lyneis lynesi lynsei lynsie lyenis lyensi lyeins
lyeisn lyesin lyesni lysnei lysnie lyseni lysein lysien lysine ilsney ilsnye
ilseny ilseyn ilsyen ilsyne ilnsey ilnsye ilnesy ilneys ilnyes ilnyse ilensy
ilenys ilesny ilesyn ileysn ileyns ilynes ilynse ilyens ilyesn ilysen ilysne
islney islnye isleny isleyn islyen islyne isnley isnlye isnely isneyl isnyel
isnyle isenly isenyl iselny iselyn iseyln iseynl isynel isynle isyenl isyeln
isylen isylne insley inslye insely inseyl insyel insyle inlsey inlsye inlesy
inleys inlyes inlyse inelsy inelys inesly inesyl ineysl ineyls inyles inylse
inyels inyesl inysel inysle iesnly iesnyl ieslny ieslyn iesyln iesynl iensly
iensyl ienlsy ienlys ienyls ienysl ielnsy ielnys ielsny ielsyn ielysn ielyns
ieynls ieynsl ieylns ieylsn ieysln ieysnl iysnel iysnle iysenl iyseln iyslen
iyslne iynsel iynsle iynesl iynels iynles iynlse iyensl iyenls iyesnl iyesln
iyelsn iyelns iylnes iylnse iylens iylesn iylsen iylsne nlisey nlisye nliesy
nlieys nliyes nliyse nlsiey nlsiye nlseiy nlseyi nlsyei nlsyie nlesiy nlesyi
nleisy nleiys nleyis nleysi nlysei nlysie nlyesi nlyeis nlyies nlyise nilsey
nilsye nilesy nileys nilyes nilyse nisley nislye nisely niseyl nisyel nisyle
niesly niesyl nielsy nielys nieyls nieysl niysel niysle niyesl niyels niyles
niylse nsiley nsilye nsiely nsieyl nsiyel nsiyle nsliey nsliye nsleiy nsleyi
nslyei nslyie nseliy nselyi nseily nseiyl nseyil nseyli nsylei nsylie nsyeli
nsyeil nsyiel nsyile neisly neisyl neilsy neilys neiyls neiysl nesily nesiyl
nesliy neslyi nesyli nesyil nelsiy nelsyi nelisy neliys nelyis nelysi neysli
neysil neylsi neylis neyils neyisl nyisel nyisle nyiesl nyiels nyiles nyilse
nysiel nysile nyseil nyseli nyslei nyslie nyesil nyesli nyeisl nyeils nyelis
nyelsi nylsei nylsie nylesi nyleis nylies nylise elinsy elinys elisny elisyn
eliysn eliyns elnisy elniys elnsiy elnsyi elnysi elnyis elsniy elsnyi elsiny
elsiyn elsyin elsyni elynsi elynis elysni elysin elyisn elyins eilnsy eilnys
eilsny eilsyn eilysn eilyns einlsy einlys einsly einsyl einysl einyls eisnly
eisnyl eislny eislyn eisyln eisynl eiynsl eiynls eiysnl eiysln eiylsn eiylns
enilsy enilys enisly enisyl eniysl eniyls enlisy enliys enlsiy enlsyi enlysi
enlyis ensliy enslyi ensily ensiyl ensyil ensyli enylsi enylis enysli enysil
enyisl enyils esinly esinyl esilny esilyn esiyln esiynl esnily esniyl esnliy
esnlyi esnyli esnyil eslniy eslnyi esliny esliyn eslyin eslyni esynli esynil
esylni esylin esyiln esyinl eyinsl eyinls eyisnl eyisln eyilsn eyilns eynisl
eynils eynsil eynsli eynlsi eynlis eysnil eysnli eysinl eysiln eyslin eyslni
eylnsi eylnis eylsni eylsin eylisn eylins ylines ylinse yliens yliesn ylisen
ylisne ylnies ylnise ylneis ylnesi ylnsei ylnsie ylenis ylensi yleins yleisn
ylesin ylesni ylsnei ylsnie ylseni ylsein ylsien ylsine yilnes yilnse yilens
yilesn yilsen yilsne yinles yinlse yinels yinesl yinsel yinsle yienls yiensl
yielns yielsn yiesln yiesnl yisnel yisnle yisenl yiseln yislen yislne yniles
ynilse yniels yniesl ynisel ynisle ynlies ynlise ynleis ynlesi ynlsei ynlsie
ynelis ynelsi yneils yneisl ynesil ynesli ynslei ynslie ynseli ynseil ynsiel
ynsile yeinls yeinsl yeilns yeilsn yeisln yeisnl yenils yenisl yenlis yenlsi
yensli yensil yelnis yelnsi yelins yelisn yelsin yelsni yesnli yesnil yeslni
yeslin yesiln yesinl ysinel ysinle ysienl ysieln ysilen ysilne ysniel ysnile
ysneil ysneli ysnlei ysnlie ysenil ysenli yseinl yseiln yselin yselni yslnei
yslnie ysleni yslein yslien ysline

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History of cryptography
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