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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: nomeus
cipher variations:
opnfvt pqogwu qrphxv rsqiyw strjzx
tuskay uvtlbz vwumca wxvndb xywoec
yzxpfd zayqge abzrhf bcasig cdbtjh
decuki efdvlj fgewmk ghfxnl higyom
ijhzpn jkiaqo kljbrp lmkcsq mnldtr

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: nomeus
Cipher: mlnvfh

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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: nomeus

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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: nomeus
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: nomeus
Cipher: abzrhf

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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: nomeus
Cipher: 334323515434

Extended Methods:
Method #1

Plaintext: nomeus
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
n o m e u s 
3 4 2 5 5 3 
3 3 3 1 4 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: nomeus
Cipher: swpnct

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Method #3

Plaintext: nomeus
method variations:
shxvoo hxvoos xvoosh
vooshx ooshxv oshxvo

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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: nomeus

all 720 cipher variations:
nomeus nomesu nomues nomuse nomsue nomseu noemus noemsu noeums noeusm noesum
noesmu nouems nouesm noumes noumse nousme nousem noseum nosemu nosuem nosume
nosmue nosmeu nmoeus nmoesu nmoues nmouse nmosue nmoseu nmeous nmeosu nmeuos
nmeuso nmesuo nmesou nmueos nmueso nmuoes nmuose nmusoe nmuseo nmseuo nmseou
nmsueo nmsuoe nmsoue nmsoeu nemous nemosu nemuos nemuso nemsuo nemsou neomus
neomsu neoums neousm neosum neosmu neuoms neuosm neumos neumso neusmo neusom
nesoum nesomu nesuom nesumo nesmuo nesmou numeos numeso numoes numose numsoe
numseo nuemos nuemso nueoms nueosm nuesom nuesmo nuoems nuoesm nuomes nuomse
nuosme nuosem nuseom nusemo nusoem nusome nusmoe nusmeo nsmeuo nsmeou nsmueo
nsmuoe nsmoue nsmoeu nsemuo nsemou nseumo nseuom nseoum nseomu nsuemo nsueom
nsumeo nsumoe nsuome nsuoem nsoeum nsoemu nsouem nsoume nsomue nsomeu onmeus
onmesu onmues onmuse onmsue onmseu onemus onemsu oneums oneusm onesum onesmu
onuems onuesm onumes onumse onusme onusem onseum onsemu onsuem onsume onsmue
onsmeu omneus omnesu omnues omnuse omnsue omnseu omenus omensu omeuns omeusn
omesun omesnu omuens omuesn omunes omunse omusne omusen omseun omsenu omsuen
omsune omsnue omsneu oemnus oemnsu oemuns oemusn oemsun oemsnu oenmus oenmsu
oenums oenusm oensum oensmu oeunms oeunsm oeumns oeumsn oeusmn oeusnm oesnum
oesnmu oesunm oesumn oesmun oesmnu oumens oumesn oumnes oumnse oumsne oumsen
ouemns ouemsn ouenms ouensm ouesnm ouesmn ounems ounesm ounmes ounmse ounsme
ounsem ousenm ousemn ousnem ousnme ousmne ousmen osmeun osmenu osmuen osmune
osmnue osmneu osemun osemnu oseumn oseunm osenum osenmu osuemn osuenm osumen
osumne osunme osunem osneum osnemu osnuem osnume osnmue osnmeu moneus monesu
monues monuse monsue monseu moenus moensu moeuns moeusn moesun moesnu mouens
mouesn mounes mounse mousne mousen moseun mosenu mosuen mosune mosnue mosneu
mnoeus mnoesu mnoues mnouse mnosue mnoseu mneous mneosu mneuos mneuso mnesuo
mnesou mnueos mnueso mnuoes mnuose mnusoe mnuseo mnseuo mnseou mnsueo mnsuoe
mnsoue mnsoeu menous menosu menuos menuso mensuo mensou meonus meonsu meouns
meousn meosun meosnu meuons meuosn meunos meunso meusno meuson mesoun mesonu
mesuon mesuno mesnuo mesnou muneos muneso munoes munose munsoe munseo muenos
muenso mueons mueosn mueson muesno muoens muoesn muones muonse muosne muosen
museon museno musoen musone musnoe musneo msneuo msneou msnueo msnuoe msnoue
msnoeu msenuo msenou mseuno mseuon mseoun mseonu msueno msueon msuneo msunoe
msuone msuoen msoeun msoenu msouen msoune msonue msoneu eomnus eomnsu eomuns
eomusn eomsun eomsnu eonmus eonmsu eonums eonusm eonsum eonsmu eounms eounsm
eoumns eoumsn eousmn eousnm eosnum eosnmu eosunm eosumn eosmun eosmnu emonus
emonsu emouns emousn emosun emosnu emnous emnosu emnuos emnuso emnsuo emnsou
emunos emunso emuons emuosn emuson emusno emsnuo emsnou emsuno emsuon emsoun
emsonu enmous enmosu enmuos enmuso enmsuo enmsou enomus enomsu enoums enousm
enosum enosmu enuoms enuosm enumos enumso enusmo enusom ensoum ensomu ensuom
ensumo ensmuo ensmou eumnos eumnso eumons eumosn eumson eumsno eunmos eunmso
eunoms eunosm eunsom eunsmo euonms euonsm euomns euomsn euosmn euosnm eusnom
eusnmo eusonm eusomn eusmon eusmno esmnuo esmnou esmuno esmuon esmoun esmonu
esnmuo esnmou esnumo esnuom esnoum esnomu esunmo esunom esumno esumon esuomn
esuonm esonum esonmu esounm esoumn esomun esomnu uomens uomesn uomnes uomnse
uomsne uomsen uoemns uoemsn uoenms uoensm uoesnm uoesmn uonems uonesm uonmes
uonmse uonsme uonsem uosenm uosemn uosnem uosnme uosmne uosmen umoens umoesn
umones umonse umosne umosen umeons umeosn umenos umenso umesno umeson umneos
umneso umnoes umnose umnsoe umnseo umseno umseon umsneo umsnoe umsone umsoen
uemons uemosn uemnos uemnso uemsno uemson ueomns ueomsn ueonms ueonsm ueosnm
ueosmn uenoms uenosm uenmos uenmso uensmo uensom uesonm uesomn uesnom uesnmo
uesmno uesmon unmeos unmeso unmoes unmose unmsoe unmseo unemos unemso uneoms
uneosm unesom unesmo unoems unoesm unomes unomse unosme unosem unseom unsemo
unsoem unsome unsmoe unsmeo usmeno usmeon usmneo usmnoe usmone usmoen usemno
usemon usenmo usenom useonm useomn usnemo usneom usnmeo usnmoe usnome usnoem
usoenm usoemn usonem usonme usomne usomen someun somenu somuen somune somnue
somneu soemun soemnu soeumn soeunm soenum soenmu souemn souenm soumen soumne
sounme sounem soneum sonemu sonuem sonume sonmue sonmeu smoeun smoenu smouen
smoune smonue smoneu smeoun smeonu smeuon smeuno smenuo smenou smueon smueno
smuoen smuone smunoe smuneo smneuo smneou smnueo smnuoe smnoue smnoeu semoun
semonu semuon semuno semnuo semnou seomun seomnu seoumn seounm seonum seonmu
seuomn seuonm seumon seumno seunmo seunom senoum senomu senuom senumo senmuo
senmou sumeon sumeno sumoen sumone sumnoe sumneo suemon suemno sueomn sueonm
suenom suenmo suoemn suoenm suomen suomne suonme suonem suneom sunemo sunoem
sunome sunmoe sunmeo snmeuo snmeou snmueo snmuoe snmoue snmoeu snemuo snemou
sneumo sneuom sneoum sneomu snuemo snueom snumeo snumoe snuome snuoem snoeum
snoemu snouem snoume snomue snomeu

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History of cryptography
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