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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: zunder
cipher variations:
avoefs bwpfgt cxqghu dyrhiv ezsijw
fatjkx gbukly hcvlmz idwmna jexnob
kfyopc lgzpqd mhaqre nibrsf ojcstg
pkdtuh qleuvi rmfvwj sngwxk tohxyl
upiyzm vqjzan wrkabo xslbcp ytmcdq

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: zunder
Cipher: afmwvi

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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: zunder

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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: zunder
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: zunder
Cipher: mhaqre

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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: zunder
Cipher: 555433415124

Extended Methods:
Method #1

Plaintext: zunder
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
z u n d e r 
5 5 3 4 5 2 
5 4 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: zunder
Cipher: zskucq

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Method #3

Plaintext: zunder
method variations:
zosvfy osvfyz svfyzo
vfyzos fyzosv yzosvf

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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: zunder

all 720 cipher variations:
zunder zundre zunedr zunerd zunred zunrde zudner zudnre zudenr zudern zudren
zudrne zuednr zuedrn zuendr zuenrd zuernd zuerdn zurden zurdne zuredn zurend
zurned zurnde znuder znudre znuedr znuerd znured znurde znduer zndure zndeur
znderu zndreu zndrue znedur znedru zneudr zneurd znerud znerdu znrdeu znrdue
znredu znreud znrued znrude zdnuer zdnure zdneur zdneru zdnreu zdnrue zduner
zdunre zduenr zduern zduren zdurne zdeunr zdeurn zdenur zdenru zdernu zderun
zdruen zdrune zdreun zdrenu zdrneu zdrnue zendur zendru zenudr zenurd zenrud
zenrdu zednur zednru zedunr zedurn zedrun zedrnu zeudnr zeudrn zeundr zeunrd
zeurnd zeurdn zerdun zerdnu zerudn zerund zernud zerndu zrndeu zrndue zrnedu
zrneud zrnued zrnude zrdneu zrdnue zrdenu zrdeun zrduen zrdune zrednu zredun
zrendu zrenud zreund zreudn zruden zrudne zruedn zruend zruned zrunde uznder
uzndre uznedr uznerd uznred uznrde uzdner uzdnre uzdenr uzdern uzdren uzdrne
uzednr uzedrn uzendr uzenrd uzernd uzerdn uzrden uzrdne uzredn uzrend uzrned
uzrnde unzder unzdre unzedr unzerd unzred unzrde undzer undzre undezr underz
undrez undrze unedzr unedrz unezdr unezrd unerzd unerdz unrdez unrdze unredz
unrezd unrzed unrzde udnzer udnzre udnezr udnerz udnrez udnrze udzner udznre
udzenr udzern udzren udzrne udeznr udezrn udenzr udenrz udernz uderzn udrzen
udrzne udrezn udrenz udrnez udrnze uendzr uendrz uenzdr uenzrd uenrzd uenrdz
uednzr uednrz uedznr uedzrn uedrzn uedrnz uezdnr uezdrn uezndr ueznrd uezrnd
uezrdn uerdzn uerdnz uerzdn uerznd uernzd uerndz urndez urndze urnedz urnezd
urnzed urnzde urdnez urdnze urdenz urdezn urdzen urdzne urednz uredzn urendz
urenzd ureznd urezdn urzden urzdne urzedn urzend urzned urznde nuzder nuzdre
nuzedr nuzerd nuzred nuzrde nudzer nudzre nudezr nuderz nudrez nudrze nuedzr
nuedrz nuezdr nuezrd nuerzd nuerdz nurdez nurdze nuredz nurezd nurzed nurzde
nzuder nzudre nzuedr nzuerd nzured nzurde nzduer nzdure nzdeur nzderu nzdreu
nzdrue nzedur nzedru nzeudr nzeurd nzerud nzerdu nzrdeu nzrdue nzredu nzreud
nzrued nzrude ndzuer ndzure ndzeur ndzeru ndzreu ndzrue nduzer nduzre nduezr
nduerz ndurez ndurze ndeuzr ndeurz ndezur ndezru nderzu nderuz ndruez ndruze
ndreuz ndrezu ndrzeu ndrzue nezdur nezdru nezudr nezurd nezrud nezrdu nedzur
nedzru neduzr nedurz nedruz nedrzu neudzr neudrz neuzdr neuzrd neurzd neurdz
nerduz nerdzu nerudz neruzd nerzud nerzdu nrzdeu nrzdue nrzedu nrzeud nrzued
nrzude nrdzeu nrdzue nrdezu nrdeuz nrduez nrduze nredzu nreduz nrezdu nrezud
nreuzd nreudz nrudez nrudze nruedz nruezd nruzed nruzde dunzer dunzre dunezr
dunerz dunrez dunrze duzner duznre duzenr duzern duzren duzrne dueznr duezrn
duenzr duenrz duernz duerzn durzen durzne durezn durenz durnez durnze dnuzer
dnuzre dnuezr dnuerz dnurez dnurze dnzuer dnzure dnzeur dnzeru dnzreu dnzrue
dnezur dnezru dneuzr dneurz dneruz dnerzu dnrzeu dnrzue dnrezu dnreuz dnruez
dnruze dznuer dznure dzneur dzneru dznreu dznrue dzuner dzunre dzuenr dzuern
dzuren dzurne dzeunr dzeurn dzenur dzenru dzernu dzerun dzruen dzrune dzreun
dzrenu dzrneu dzrnue denzur denzru denuzr denurz denruz denrzu deznur deznru
dezunr dezurn dezrun dezrnu deuznr deuzrn deunzr deunrz deurnz deurzn derzun
derznu deruzn derunz dernuz dernzu drnzeu drnzue drnezu drneuz drnuez drnuze
drzneu drznue drzenu drzeun drzuen drzune dreznu drezun drenzu drenuz dreunz
dreuzn druzen druzne druezn druenz drunez drunze eundzr eundrz eunzdr eunzrd
eunrzd eunrdz eudnzr eudnrz eudznr eudzrn eudrzn eudrnz euzdnr euzdrn euzndr
euznrd euzrnd euzrdn eurdzn eurdnz eurzdn eurznd eurnzd eurndz enudzr enudrz
enuzdr enuzrd enurzd enurdz enduzr endurz endzur endzru endrzu endruz enzdur
enzdru enzudr enzurd enzrud enzrdu enrdzu enrduz enrzdu enrzud enruzd enrudz
ednuzr ednurz ednzur ednzru ednrzu ednruz edunzr edunrz eduznr eduzrn edurzn
edurnz edzunr edzurn edznur edznru edzrnu edzrun edruzn edrunz edrzun edrznu
edrnzu edrnuz ezndur ezndru eznudr eznurd eznrud eznrdu ezdnur ezdnru ezdunr
ezdurn ezdrun ezdrnu ezudnr ezudrn ezundr ezunrd ezurnd ezurdn ezrdun ezrdnu
ezrudn ezrund ezrnud ezrndu erndzu ernduz ernzdu ernzud ernuzd ernudz erdnzu
erdnuz erdznu erdzun erduzn erdunz erzdnu erzdun erzndu erznud erzund erzudn
erudzn erudnz eruzdn eruznd erunzd erundz rundez rundze runedz runezd runzed
runzde rudnez rudnze rudenz rudezn rudzen rudzne ruednz ruedzn ruendz ruenzd
rueznd ruezdn ruzden ruzdne ruzedn ruzend ruzned ruznde rnudez rnudze rnuedz
rnuezd rnuzed rnuzde rnduez rnduze rndeuz rndezu rndzeu rndzue rneduz rnedzu
rneudz rneuzd rnezud rnezdu rnzdeu rnzdue rnzedu rnzeud rnzued rnzude rdnuez
rdnuze rdneuz rdnezu rdnzeu rdnzue rdunez rdunze rduenz rduezn rduzen rduzne
rdeunz rdeuzn rdenuz rdenzu rdeznu rdezun rdzuen rdzune rdzeun rdzenu rdzneu
rdznue renduz rendzu renudz renuzd renzud renzdu rednuz rednzu redunz reduzn
redzun redznu reudnz reudzn reundz reunzd reuznd reuzdn rezdun rezdnu rezudn
rezund reznud rezndu rzndeu rzndue rznedu rzneud rznued rznude rzdneu rzdnue
rzdenu rzdeun rzduen rzdune rzednu rzedun rzendu rzenud rzeund rzeudn rzuden
rzudne rzuedn rzuend rzuned rzunde

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History of cryptography
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