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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: ilonka
cipher variations:
jmpolb knqpmc lorqnd mpsroe nqtspf
orutqg psvurh qtwvsi ruxwtj svyxuk
twzyvl uxazwm vybaxn wzcbyo xadczp
ybedaq zcfebr adgfcs behgdt cfiheu
dgjifv ehkjgw filkhx gjmliy hknmjz

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: ilonka
Cipher: rolmpz

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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: ilonka

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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: ilonka
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: ilonka
Cipher: vybaxn

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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: ilonka
Cipher: 421343335211

Extended Methods:
Method #1

Plaintext: ilonka
method variations:

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

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Method #3

Plaintext: ilonka
method variations:
bsnxbq snxbqb nxbqbs
xbqbsn bqbsnx qbsnxb

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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: ilonka

all 720 cipher variations:
ilonka ilonak ilokna ilokan iloakn iloank ilnoka ilnoak ilnkoa ilnkao ilnako
ilnaok ilknoa ilknao ilkona ilkoan ilkaon ilkano ilanko ilanok ilakno ilakon
ilaokn ilaonk iolnka iolnak iolkna iolkan iolakn iolank ionlka ionlak ionkla
ionkal ionakl ionalk ioknla ioknal ioklna ioklan iokaln iokanl ioankl ioanlk
ioaknl ioakln ioalkn ioalnk inolka inolak inokla inokal inoakl inoalk inloka
inloak inlkoa inlkao inlako inlaok inkloa inklao inkola inkoal inkaol inkalo
inalko inalok inaklo inakol inaokl inaolk ikonla ikonal ikolna ikolan ikoaln
ikoanl iknola iknoal iknloa iknlao iknalo iknaol iklnoa iklnao iklona ikloan
iklaon iklano ikanlo ikanol ikalno ikalon ikaoln ikaonl iaonkl iaonlk iaoknl
iaokln iaolkn iaolnk ianokl ianolk iankol ianklo ianlko ianlok iaknol iaknlo
iakonl iakoln iaklon iaklno ialnko ialnok ialkno ialkon ialokn ialonk lionka
lionak liokna liokan lioakn lioank linoka linoak linkoa linkao linako linaok
liknoa liknao likona likoan likaon likano lianko lianok liakno liakon liaokn
liaonk loinka loinak loikna loikan loiakn loiank lonika loniak lonkia lonkai
lonaki lonaik loknia loknai lokina lokian lokain lokani loanki loanik loakni
loakin loaikn loaink lnoika lnoiak lnokia lnokai lnoaki lnoaik lnioka lnioak
lnikoa lnikao lniako lniaok lnkioa lnkiao lnkoia lnkoai lnkaoi lnkaio lnaiko
lnaiok lnakio lnakoi lnaoki lnaoik lkonia lkonai lkoina lkoian lkoain lkoani
lknoia lknoai lknioa lkniao lknaio lknaoi lkinoa lkinao lkiona lkioan lkiaon
lkiano lkanio lkanoi lkaino lkaion lkaoin lkaoni laonki laonik laokni laokin
laoikn laoink lanoki lanoik lankoi lankio laniko laniok laknoi laknio lakoni
lakoin lakion lakino lainko lainok laikno laikon laiokn laionk olinka olinak
olikna olikan oliakn oliank olnika olniak olnkia olnkai olnaki olnaik olknia
olknai olkina olkian olkain olkani olanki olanik olakni olakin olaikn olaink
oilnka oilnak oilkna oilkan oilakn oilank oinlka oinlak oinkla oinkal oinakl
oinalk oiknla oiknal oiklna oiklan oikaln oikanl oiankl oianlk oiaknl oiakln
oialkn oialnk onilka onilak onikla onikal oniakl onialk onlika onliak onlkia
onlkai onlaki onlaik onklia onklai onkila onkial onkail onkali onalki onalik
onakli onakil onaikl onailk okinla okinal okilna okilan okialn okianl oknila
oknial oknlia oknlai oknali oknail oklnia oklnai oklina oklian oklain oklani
okanli okanil okalni okalin okailn okainl oainkl oainlk oaiknl oaikln oailkn
oailnk oanikl oanilk oankil oankli oanlki oanlik oaknil oaknli oakinl oakiln
oaklin oaklni oalnki oalnik oalkni oalkin oalikn oalink nloika nloiak nlokia
nlokai nloaki nloaik nlioka nlioak nlikoa nlikao nliako nliaok nlkioa nlkiao
nlkoia nlkoai nlkaoi nlkaio nlaiko nlaiok nlakio nlakoi nlaoki nlaoik nolika
noliak nolkia nolkai nolaki nolaik noilka noilak noikla noikal noiakl noialk
nokila nokial noklia noklai nokali nokail noaikl noailk noakil noakli noalki
noalik niolka niolak niokla niokal nioakl nioalk niloka niloak nilkoa nilkao
nilako nilaok nikloa niklao nikola nikoal nikaol nikalo nialko nialok niaklo
niakol niaokl niaolk nkoila nkoial nkolia nkolai nkoali nkoail nkiola nkioal
nkiloa nkilao nkialo nkiaol nklioa nkliao nkloia nkloai nklaoi nklaio nkailo
nkaiol nkalio nkaloi nkaoli nkaoil naoikl naoilk naokil naokli naolki naolik
naiokl naiolk naikol naiklo nailko nailok nakiol nakilo nakoil nakoli nakloi
naklio naliko naliok nalkio nalkoi naloki naloik klonia klonai kloina kloian
kloain kloani klnoia klnoai klnioa klniao klnaio klnaoi klinoa klinao kliona
klioan kliaon kliano klanio klanoi klaino klaion klaoin klaoni kolnia kolnai
kolina kolian kolain kolani konlia konlai konila konial konail konali koinla
koinal koilna koilan koialn koianl koanil koanli koainl koailn koalin koalni
knolia knolai knoila knoial knoail knoali knloia knloai knlioa knliao knlaio
knlaoi kniloa knilao kniola knioal kniaol knialo knalio knaloi knailo knaiol
knaoil knaoli kionla kional kiolna kiolan kioaln kioanl kinola kinoal kinloa
kinlao kinalo kinaol kilnoa kilnao kilona kiloan kilaon kilano kianlo kianol
kialno kialon kiaoln kiaonl kaonil kaonli kaoinl kaoiln kaolin kaolni kanoil
kanoli kaniol kanilo kanlio kanloi kainol kainlo kaionl kaioln kailon kailno
kalnio kalnoi kalino kalion kaloin kaloni alonki alonik alokni alokin aloikn
aloink alnoki alnoik alnkoi alnkio alniko alniok alknoi alknio alkoni alkoin
alkion alkino alinko alinok alikno alikon aliokn alionk aolnki aolnik aolkni
aolkin aolikn aolink aonlki aonlik aonkli aonkil aonikl aonilk aoknli aoknil
aoklni aoklin aokiln aokinl aoinkl aoinlk aoiknl aoikln aoilkn aoilnk anolki
anolik anokli anokil anoikl anoilk anloki anloik anlkoi anlkio anliko anliok
ankloi anklio ankoli ankoil ankiol ankilo anilko anilok aniklo anikol aniokl
aniolk akonli akonil akolni akolin akoiln akoinl aknoli aknoil aknloi aknlio
aknilo akniol aklnoi aklnio akloni akloin aklion aklino akinlo akinol akilno
akilon akioln akionl aionkl aionlk aioknl aiokln aiolkn aiolnk ainokl ainolk
ainkol ainklo ainlko ainlok aiknol aiknlo aikonl aikoln aiklon aiklno ailnko
ailnok ailkno ailkon ailokn ailonk

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History of cryptography
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