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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: netadm
cipher variations:
ofuben pgvcfo qhwdgp rixehq sjyfir
tkzgjs ulahkt vmbilu wncjmv xodknw
ypelox zqfmpy argnqz bshora ctipsb
dujqtc evkrud fwlsve gxmtwf hynuxg
izovyh japwzi kbqxaj lcrybk mdszcl

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: netadm
Cipher: mvgzwn

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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: netadm

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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: netadm
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: netadm
Cipher: argnqz

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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: netadm
Cipher: 335144114123

Extended Methods:
Method #1

Plaintext: netadm
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
n e t a d m 
3 5 4 1 4 2 
3 1 4 1 1 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: netadm
Cipher: xdicdl

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Method #3

Plaintext: netadm
method variations:
xqdqfn qdqfnx dqfnxq
qfnxqd fnxqdq nxqdqf

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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: netadm

all 720 cipher variations:
netadm netamd netdam netdma netmda netmad neatdm neatmd neadtm neadmt neamdt
neamtd nedatm nedamt nedtam nedtma nedmta nedmat nemadt nematd nemdat nemdta
nemtda nemtad nteadm nteamd ntedam ntedma ntemda ntemad ntaedm ntaemd ntadem
ntadme ntamde ntamed ntdaem ntdame ntdeam ntdema ntdmea ntdmae ntmade ntmaed
ntmdae ntmdea ntmeda ntmead natedm natemd natdem natdme natmde natmed naetdm
naetmd naedtm naedmt naemdt naemtd nadetm nademt nadtem nadtme nadmte nadmet
namedt nametd namdet namdte namtde namted ndtaem ndtame ndteam ndtema ndtmea
ndtmae ndatem ndatme ndaetm ndaemt ndamet ndamte ndeatm ndeamt ndetam ndetma
ndemta ndemat ndmaet ndmate ndmeat ndmeta ndmtea ndmtae nmtade nmtaed nmtdae
nmtdea nmteda nmtead nmatde nmated nmadte nmadet nmaedt nmaetd nmdate nmdaet
nmdtae nmdtea nmdeta nmdeat nmeadt nmeatd nmedat nmedta nmetda nmetad entadm
entamd entdam entdma entmda entmad enatdm enatmd enadtm enadmt enamdt enamtd
endatm endamt endtam endtma endmta endmat enmadt enmatd enmdat enmdta enmtda
enmtad etnadm etnamd etndam etndma etnmda etnmad etandm etanmd etadnm etadmn
etamdn etamnd etdanm etdamn etdnam etdnma etdmna etdman etmadn etmand etmdan
etmdna etmnda etmnad eatndm eatnmd eatdnm eatdmn eatmdn eatmnd eantdm eantmd
eandtm eandmt eanmdt eanmtd eadntm eadnmt eadtnm eadtmn eadmtn eadmnt eamndt
eamntd eamdnt eamdtn eamtdn eamtnd edtanm edtamn edtnam edtnma edtmna edtman
edatnm edatmn edantm edanmt edamnt edamtn ednatm ednamt edntam edntma ednmta
ednmat edmant edmatn edmnat edmnta edmtna edmtan emtadn emtand emtdan emtdna
emtnda emtnad ematdn ematnd emadtn emadnt emandt emantd emdatn emdant emdtan
emdtna emdnta emdnat emnadt emnatd emndat emndta emntda emntad tenadm tenamd
tendam tendma tenmda tenmad teandm teanmd teadnm teadmn teamdn teamnd tedanm
tedamn tednam tednma tedmna tedman temadn temand temdan temdna temnda temnad
tneadm tneamd tnedam tnedma tnemda tnemad tnaedm tnaemd tnadem tnadme tnamde
tnamed tndaem tndame tndeam tndema tndmea tndmae tnmade tnmaed tnmdae tnmdea
tnmeda tnmead tanedm tanemd tandem tandme tanmde tanmed taendm taenmd taednm
taedmn taemdn taemnd tadenm tademn tadnem tadnme tadmne tadmen tamedn tamend
tamden tamdne tamnde tamned tdnaem tdname tdneam tdnema tdnmea tdnmae tdanem
tdanme tdaenm tdaemn tdamen tdamne tdeanm tdeamn tdenam tdenma tdemna tdeman
tdmaen tdmane tdmean tdmena tdmnea tdmnae tmnade tmnaed tmndae tmndea tmneda
tmnead tmande tmaned tmadne tmaden tmaedn tmaend tmdane tmdaen tmdnae tmdnea
tmdena tmdean tmeadn tmeand tmedan tmedna tmenda tmenad aetndm aetnmd aetdnm
aetdmn aetmdn aetmnd aentdm aentmd aendtm aendmt aenmdt aenmtd aedntm aednmt
aedtnm aedtmn aedmtn aedmnt aemndt aemntd aemdnt aemdtn aemtdn aemtnd atendm
atenmd atednm atedmn atemdn atemnd atnedm atnemd atndem atndme atnmde atnmed
atdnem atdnme atdenm atdemn atdmen atdmne atmnde atmned atmdne atmden atmedn
atmend antedm antemd antdem antdme antmde antmed anetdm anetmd anedtm anedmt
anemdt anemtd andetm andemt andtem andtme andmte andmet anmedt anmetd anmdet
anmdte anmtde anmted adtnem adtnme adtenm adtemn adtmen adtmne adntem adntme
adnetm adnemt adnmet adnmte adentm adenmt adetnm adetmn ademtn ademnt admnet
admnte adment admetn admten admtne amtnde amtned amtdne amtden amtedn amtend
amntde amnted amndte amndet amnedt amnetd amdnte amdnet amdtne amdten amdetn
amdent amendt amentd amednt amedtn ametdn ametnd detanm detamn detnam detnma
detmna detman deatnm deatmn deantm deanmt deamnt deamtn denatm denamt dentam
dentma denmta denmat demant dematn demnat demnta demtna demtan dteanm dteamn
dtenam dtenma dtemna dteman dtaenm dtaemn dtanem dtanme dtamne dtamen dtnaem
dtname dtneam dtnema dtnmea dtnmae dtmane dtmaen dtmnae dtmnea dtmena dtmean
datenm datemn datnem datnme datmne datmen daetnm daetmn daentm daenmt daemnt
daemtn danetm danemt dantem dantme danmte danmet dament dametn damnet damnte
damtne damten dntaem dntame dnteam dntema dntmea dntmae dnatem dnatme dnaetm
dnaemt dnamet dnamte dneatm dneamt dnetam dnetma dnemta dnemat dnmaet dnmate
dnmeat dnmeta dnmtea dnmtae dmtane dmtaen dmtnae dmtnea dmtena dmtean dmatne
dmaten dmante dmanet dmaent dmaetn dmnate dmnaet dmntae dmntea dmneta dmneat
dmeant dmeatn dmenat dmenta dmetna dmetan metadn metand metdan metdna metnda
metnad meatdn meatnd meadtn meadnt meandt meantd medatn medant medtan medtna
mednta mednat menadt menatd mendat mendta mentda mentad mteadn mteand mtedan
mtedna mtenda mtenad mtaedn mtaend mtaden mtadne mtande mtaned mtdaen mtdane
mtdean mtdena mtdnea mtdnae mtnade mtnaed mtndae mtndea mtneda mtnead matedn
matend matden matdne matnde matned maetdn maetnd maedtn maednt maendt maentd
madetn madent madten madtne madnte madnet manedt manetd mandet mandte mantde
manted mdtaen mdtane mdtean mdtena mdtnea mdtnae mdaten mdatne mdaetn mdaent
mdanet mdante mdeatn mdeant mdetan mdetna mdenta mdenat mdnaet mdnate mdneat
mdneta mdntea mdntae mntade mntaed mntdae mntdea mnteda mntead mnatde mnated
mnadte mnadet mnaedt mnaetd mndate mndaet mndtae mndtea mndeta mndeat mneadt
mneatd mnedat mnedta mnetda mnetad

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History of cryptography
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