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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: eklund
cipher variations:
flmvoe gmnwpf hnoxqg iopyrh jpqzsi
kqratj lrsbuk mstcvl ntudwm ouvexn
pvwfyo qwxgzp rxyhaq syzibr tzajcs
uabkdt vbcleu wcdmfv xdengw yefohx
zfgpiy aghqjz bhirka cijslb djktmc

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: eklund
Cipher: vpofmw

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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: eklund

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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: eklund
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: eklund
Cipher: rxyhaq

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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: eklund
Cipher: 515213543341

Extended Methods:
Method #1

Plaintext: eklund
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
e k l u n d 
5 5 1 5 3 4 
1 2 3 4 3 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: eklund
Cipher: zvsfsc

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Method #3

Plaintext: eklund
method variations:
vbxosv bxosvv xosvvb
osvvbx svvbxo vvbxos

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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: eklund

all 720 cipher variations:
eklund ekludn eklnud eklndu ekldnu ekldun ekulnd ekuldn ekunld ekundl ekudnl
ekudln eknuld eknudl eknlud eknldu ekndlu ekndul ekdunl ekduln ekdnul ekdnlu
ekdlnu ekdlun elkund elkudn elknud elkndu elkdnu elkdun eluknd elukdn elunkd
elundk eludnk eludkn elnukd elnudk elnkud elnkdu elndku elnduk eldunk eldukn
eldnuk eldnku eldknu eldkun eulknd eulkdn eulnkd eulndk euldnk euldkn euklnd
eukldn euknld eukndl eukdnl eukdln eunkld eunkdl eunlkd eunldk eundlk eundkl
eudknl eudkln eudnkl eudnlk eudlnk eudlkn enlukd enludk enlkud enlkdu enldku
enlduk enulkd enuldk enukld enukdl enudkl enudlk enkuld enkudl enklud enkldu
enkdlu enkdul endukl endulk endkul endklu endlku endluk edlunk edlukn edlnuk
edlnku edlknu edlkun edulnk edulkn edunlk edunkl eduknl edukln ednulk ednukl
ednluk ednlku ednklu ednkul edkunl edkuln edknul edknlu edklnu edklun kelund
keludn kelnud kelndu keldnu keldun keulnd keuldn keunld keundl keudnl keudln
kenuld kenudl kenlud kenldu kendlu kendul kedunl keduln kednul kednlu kedlnu
kedlun kleund kleudn klenud klendu klednu kledun kluend kluedn kluned klunde
kludne kluden klnued klnude klneud klnedu klndeu klndue kldune klduen kldnue
kldneu kldenu kldeun kulend kuledn kulned kulnde kuldne kulden kuelnd kueldn
kuenld kuendl kuednl kuedln kuneld kunedl kunled kunlde kundle kundel kudenl
kudeln kudnel kudnle kudlne kudlen knlued knlude knleud knledu knldeu knldue
knuled knulde knueld knuedl knudel knudle kneuld kneudl knelud kneldu knedlu
knedul knduel kndule kndeul kndelu kndleu kndlue kdlune kdluen kdlnue kdlneu
kdlenu kdleun kdulne kdulen kdunle kdunel kduenl kdueln kdnule kdnuel kdnlue
kdnleu kdnelu kdneul kdeunl kdeuln kdenul kdenlu kdelnu kdelun lkeund lkeudn
lkenud lkendu lkednu lkedun lkuend lkuedn lkuned lkunde lkudne lkuden lknued
lknude lkneud lknedu lkndeu lkndue lkdune lkduen lkdnue lkdneu lkdenu lkdeun
lekund lekudn leknud lekndu lekdnu lekdun leuknd leukdn leunkd leundk leudnk
leudkn lenukd lenudk lenkud lenkdu lendku lenduk ledunk ledukn lednuk lednku
ledknu ledkun lueknd luekdn luenkd luendk luednk luedkn lukend lukedn lukned
luknde lukdne lukden lunked lunkde lunekd lunedk lundek lundke ludkne ludken
ludnke ludnek ludenk ludekn lneukd lneudk lnekud lnekdu lnedku lneduk lnuekd
lnuedk lnuked lnukde lnudke lnudek lnkued lnkude lnkeud lnkedu lnkdeu lnkdue
lnduke lnduek lndkue lndkeu lndeku lndeuk ldeunk ldeukn ldenuk ldenku ldeknu
ldekun lduenk lduekn ldunek ldunke ldukne lduken ldnuek ldnuke ldneuk ldneku
ldnkeu ldnkue ldkune ldkuen ldknue ldkneu ldkenu ldkeun uklend ukledn uklned
uklnde ukldne uklden ukelnd ukeldn ukenld ukendl ukednl ukedln ukneld uknedl
uknled uknlde ukndle ukndel ukdenl ukdeln ukdnel ukdnle ukdlne ukdlen ulkend
ulkedn ulkned ulknde ulkdne ulkden uleknd ulekdn ulenkd ulendk ulednk uledkn
ulnekd ulnedk ulnked ulnkde ulndke ulndek uldenk uldekn uldnek uldnke uldkne
uldken uelknd uelkdn uelnkd uelndk ueldnk ueldkn ueklnd uekldn ueknld uekndl
uekdnl uekdln uenkld uenkdl uenlkd uenldk uendlk uendkl uedknl uedkln uednkl
uednlk uedlnk uedlkn unlekd unledk unlked unlkde unldke unldek unelkd uneldk
unekld unekdl unedkl unedlk unkeld unkedl unkled unklde unkdle unkdel undekl
undelk undkel undkle undlke undlek udlenk udlekn udlnek udlnke udlkne udlken
udelnk udelkn udenlk udenkl udeknl udekln udnelk udnekl udnlek udnlke udnkle
udnkel udkenl udkeln udknel udknle udklne udklen nklued nklude nkleud nkledu
nkldeu nkldue nkuled nkulde nkueld nkuedl nkudel nkudle nkeuld nkeudl nkelud
nkeldu nkedlu nkedul nkduel nkdule nkdeul nkdelu nkdleu nkdlue nlkued nlkude
nlkeud nlkedu nlkdeu nlkdue nluked nlukde nluekd nluedk nludek nludke nleukd
nleudk nlekud nlekdu nledku nleduk nlduek nlduke nldeuk nldeku nldkeu nldkue
nulked nulkde nulekd nuledk nuldek nuldke nukled nuklde nukeld nukedl nukdel
nukdle nuekld nuekdl nuelkd nueldk nuedlk nuedkl nudkel nudkle nudekl nudelk
nudlek nudlke nelukd neludk nelkud nelkdu neldku nelduk neulkd neuldk neukld
neukdl neudkl neudlk nekuld nekudl neklud nekldu nekdlu nekdul nedukl nedulk
nedkul nedklu nedlku nedluk ndluek ndluke ndleuk ndleku ndlkeu ndlkue ndulek
ndulke nduelk nduekl ndukel ndukle ndeulk ndeukl ndeluk ndelku ndeklu ndekul
ndkuel ndkule ndkeul ndkelu ndkleu ndklue dklune dkluen dklnue dklneu dklenu
dkleun dkulne dkulen dkunle dkunel dkuenl dkueln dknule dknuel dknlue dknleu
dknelu dkneul dkeunl dkeuln dkenul dkenlu dkelnu dkelun dlkune dlkuen dlknue
dlkneu dlkenu dlkeun dlukne dluken dlunke dlunek dluenk dluekn dlnuke dlnuek
dlnkue dlnkeu dlneku dlneuk dleunk dleukn dlenuk dlenku dleknu dlekun dulkne
dulken dulnke dulnek dulenk dulekn duklne duklen duknle duknel dukenl dukeln
dunkle dunkel dunlke dunlek dunelk dunekl dueknl duekln duenkl duenlk duelnk
duelkn dnluke dnluek dnlkue dnlkeu dnleku dnleuk dnulke dnulek dnukle dnukel
dnuekl dnuelk dnkule dnkuel dnklue dnkleu dnkelu dnkeul dneukl dneulk dnekul
dneklu dnelku dneluk delunk delukn delnuk delnku delknu delkun deulnk deulkn
deunlk deunkl deuknl deukln denulk denukl denluk denlku denklu denkul dekunl
dekuln deknul deknlu deklnu deklun

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History of cryptography
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