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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: whatso
cipher variations:
xibutp yjcvuq zkdwvr alexws bmfyxt
cngzyu dohazv epibaw fqjcbx grkdcy
hsledz itmfea jungfb kvohgc lwpihd
mxqjie nyrkjf ozslkg patmlh qbunmi
rcvonj sdwpok texqpl ufyrqm vgzsrn

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: whatso
Cipher: dszghl

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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: whatso

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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: whatso
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: whatso
Cipher: jungfb

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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: whatso
Cipher: 253211443443

Extended Methods:
Method #1

Plaintext: whatso
method variations:

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

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Method #3

Plaintext: whatso
method variations:
pbqoth bqothp qothpb
othpbq thpbqo hpbqot

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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: whatso

all 720 cipher variations:
whatso whatos whasto whasot whaost whaots whtaso whtaos whtsao whtsoa whtosa
whtoas whstao whstoa whsato whsaot whsoat whsota whotsa whotas whosta whosat
whoast whoats wahtso wahtos wahsto wahsot wahost wahots wathso wathos watsho
watsoh watosh watohs wastho wastoh washto washot wasoht wasoth waotsh waoths
waosth waosht waohst waohts wtahso wtahos wtasho wtasoh wtaosh wtaohs wthaso
wthaos wthsao wthsoa wthosa wthoas wtshao wtshoa wtsaho wtsaoh wtsoah wtsoha
wtohsa wtohas wtosha wtosah wtoash wtoahs wsatho wsatoh wsahto wsahot wsaoht
wsaoth wstaho wstaoh wsthao wsthoa wstoha wstoah wshtao wshtoa wshato wshaot
wshoat wshota wsotha wsotah wsohta wsohat wsoaht wsoath woatsh woaths woasth
woasht woahst woahts wotash wotahs wotsah wotsha wothsa wothas wostah wostha
wosath wosaht woshat woshta wohtsa wohtas wohsta wohsat wohast wohats hwatso
hwatos hwasto hwasot hwaost hwaots hwtaso hwtaos hwtsao hwtsoa hwtosa hwtoas
hwstao hwstoa hwsato hwsaot hwsoat hwsota hwotsa hwotas hwosta hwosat hwoast
hwoats hawtso hawtos hawsto hawsot hawost hawots hatwso hatwos hatswo hatsow
hatosw hatows hastwo hastow haswto haswot hasowt hasotw haotsw haotws haostw
haoswt haowst haowts htawso htawos htaswo htasow htaosw htaows htwaso htwaos
htwsao htwsoa htwosa htwoas htswao htswoa htsawo htsaow htsoaw htsowa htowsa
htowas htoswa htosaw htoasw htoaws hsatwo hsatow hsawto hsawot hsaowt hsaotw
hstawo hstaow hstwao hstwoa hstowa hstoaw hswtao hswtoa hswato hswaot hswoat
hswota hsotwa hsotaw hsowta hsowat hsoawt hsoatw hoatsw hoatws hoastw hoaswt
hoawst hoawts hotasw hotaws hotsaw hotswa hotwsa hotwas hostaw hostwa hosatw
hosawt hoswat hoswta howtsa howtas howsta howsat howast howats ahwtso ahwtos
ahwsto ahwsot ahwost ahwots ahtwso ahtwos ahtswo ahtsow ahtosw ahtows ahstwo
ahstow ahswto ahswot ahsowt ahsotw ahotsw ahotws ahostw ahoswt ahowst ahowts
awhtso awhtos awhsto awhsot awhost awhots awthso awthos awtsho awtsoh awtosh
awtohs awstho awstoh awshto awshot awsoht awsoth awotsh awoths awosth awosht
awohst awohts atwhso atwhos atwsho atwsoh atwosh atwohs athwso athwos athswo
athsow athosw athows atshwo atshow atswho atswoh atsowh atsohw atohsw atohws
atoshw atoswh atowsh atowhs aswtho aswtoh aswhto aswhot aswoht aswoth astwho
astwoh asthwo asthow astohw astowh ashtwo ashtow ashwto ashwot ashowt ashotw
asothw asotwh asohtw asohwt asowht asowth aowtsh aowths aowsth aowsht aowhst
aowhts aotwsh aotwhs aotswh aotshw aothsw aothws aostwh aosthw aoswth aoswht
aoshwt aoshtw aohtsw aohtws aohstw aohswt aohwst aohwts thawso thawos thaswo
thasow thaosw thaows thwaso thwaos thwsao thwsoa thwosa thwoas thswao thswoa
thsawo thsaow thsoaw thsowa thowsa thowas thoswa thosaw thoasw thoaws tahwso
tahwos tahswo tahsow tahosw tahows tawhso tawhos tawsho tawsoh tawosh tawohs
taswho taswoh tashwo tashow tasohw tasowh taowsh taowhs taoswh taoshw taohsw
taohws twahso twahos twasho twasoh twaosh twaohs twhaso twhaos twhsao twhsoa
twhosa twhoas twshao twshoa twsaho twsaoh twsoah twsoha twohsa twohas twosha
twosah twoash twoahs tsawho tsawoh tsahwo tsahow tsaohw tsaowh tswaho tswaoh
tswhao tswhoa tswoha tswoah tshwao tshwoa tshawo tshaow tshoaw tshowa tsowha
tsowah tsohwa tsohaw tsoahw tsoawh toawsh toawhs toaswh toashw toahsw toahws
towash towahs towsah towsha towhsa towhas toswah toswha tosawh tosahw toshaw
toshwa tohwsa tohwas tohswa tohsaw tohasw tohaws shatwo shatow shawto shawot
shaowt shaotw shtawo shtaow shtwao shtwoa shtowa shtoaw shwtao shwtoa shwato
shwaot shwoat shwota shotwa shotaw showta showat shoawt shoatw sahtwo sahtow
sahwto sahwot sahowt sahotw sathwo sathow satwho satwoh satowh satohw sawtho
sawtoh sawhto sawhot sawoht sawoth saotwh saothw saowth saowht saohwt saohtw
stahwo stahow stawho stawoh staowh staohw sthawo sthaow sthwao sthwoa sthowa
sthoaw stwhao stwhoa stwaho stwaoh stwoah stwoha stohwa stohaw stowha stowah
stoawh stoahw swatho swatoh swahto swahot swaoht swaoth swtaho swtaoh swthao
swthoa swtoha swtoah swhtao swhtoa swhato swhaot swhoat swhota swotha swotah
swohta swohat swoaht swoath soatwh soathw soawth soawht soahwt soahtw sotawh
sotahw sotwah sotwha sothwa sothaw sowtah sowtha sowath sowaht sowhat sowhta
sohtwa sohtaw sohwta sohwat sohawt sohatw ohatsw ohatws ohastw ohaswt ohawst
ohawts ohtasw ohtaws ohtsaw ohtswa ohtwsa ohtwas ohstaw ohstwa ohsatw ohsawt
ohswat ohswta ohwtsa ohwtas ohwsta ohwsat ohwast ohwats oahtsw oahtws oahstw
oahswt oahwst oahwts oathsw oathws oatshw oatswh oatwsh oatwhs oasthw oastwh
oashtw oashwt oaswht oaswth oawtsh oawths oawsth oawsht oawhst oawhts otahsw
otahws otashw otaswh otawsh otawhs othasw othaws othsaw othswa othwsa othwas
otshaw otshwa otsahw otsawh otswah otswha otwhsa otwhas otwsha otwsah otwash
otwahs osathw osatwh osahtw osahwt osawht osawth ostahw ostawh osthaw osthwa
ostwha ostwah oshtaw oshtwa oshatw oshawt oshwat oshwta oswtha oswtah oswhta
oswhat oswaht oswath owatsh owaths owasth owasht owahst owahts owtash owtahs
owtsah owtsha owthsa owthas owstah owstha owsath owsaht owshat owshta owhtsa
owhtas owhsta owhsat owhast owhats

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History of cryptography
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