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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: strunk
cipher variations:
tusvol uvtwpm vwuxqn wxvyro xywzsp
yzxatq zaybur abzcvs bcadwt cdbexu
decfyv efdgzw fgehax ghfiby higjcz
ijhkda jkileb kljmfc lmkngd mnlohe
nompif opnqjg pqorkh qrpsli rsqtmj

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: strunk
Cipher: hgifmp

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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: strunk

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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: strunk
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: strunk
Cipher: fgehax

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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: strunk
Cipher: 344424543352

Extended Methods:
Method #1

Plaintext: strunk
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
s t r u n k 
3 4 2 5 3 5 
4 4 4 4 3 2 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: strunk
Cipher: swxtth

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Method #3

Plaintext: strunk
method variations:
tiyoxm iyoxmt yoxmti
oxmtiy xmtiyo mtiyox

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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: strunk

all 720 cipher variations:
strunk strukn strnuk strnku strknu strkun sturnk sturkn stunrk stunkr stuknr
stukrn stnurk stnukr stnruk stnrku stnkru stnkur stkunr stkurn stknur stknru
stkrnu stkrun srtunk srtukn srtnuk srtnku srtknu srtkun srutnk srutkn sruntk
srunkt sruknt sruktn srnutk srnukt srntuk srntku srnktu srnkut srkunt srkutn
srknut srkntu srktnu srktun surtnk surtkn surntk surnkt surknt surktn sutrnk
sutrkn sutnrk sutnkr sutknr sutkrn suntrk suntkr sunrtk sunrkt sunkrt sunktr
suktnr suktrn sukntr suknrt sukrnt sukrtn snrutk snrukt snrtuk snrtku snrktu
snrkut snurtk snurkt snutrk snutkr snuktr snukrt snturk sntukr sntruk sntrku
sntkru sntkur snkutr snkurt snktur snktru snkrtu snkrut skrunt skrutn skrnut
skrntu skrtnu skrtun skurnt skurtn skunrt skuntr skutnr skutrn sknurt sknutr
sknrut sknrtu skntru skntur sktunr skturn sktnur sktnru sktrnu sktrun tsrunk
tsrukn tsrnuk tsrnku tsrknu tsrkun tsurnk tsurkn tsunrk tsunkr tsuknr tsukrn
tsnurk tsnukr tsnruk tsnrku tsnkru tsnkur tskunr tskurn tsknur tsknru tskrnu
tskrun trsunk trsukn trsnuk trsnku trsknu trskun trusnk truskn trunsk trunks
trukns truksn trnusk trnuks trnsuk trnsku trnksu trnkus trkuns trkusn trknus
trknsu trksnu trksun tursnk turskn turnsk turnks turkns turksn tusrnk tusrkn
tusnrk tusnkr tusknr tuskrn tunsrk tunskr tunrsk tunrks tunkrs tunksr tuksnr
tuksrn tuknsr tuknrs tukrns tukrsn tnrusk tnruks tnrsuk tnrsku tnrksu tnrkus
tnursk tnurks tnusrk tnuskr tnuksr tnukrs tnsurk tnsukr tnsruk tnsrku tnskru
tnskur tnkusr tnkurs tnksur tnksru tnkrsu tnkrus tkruns tkrusn tkrnus tkrnsu
tkrsnu tkrsun tkurns tkursn tkunrs tkunsr tkusnr tkusrn tknurs tknusr tknrus
tknrsu tknsru tknsur tksunr tksurn tksnur tksnru tksrnu tksrun rtsunk rtsukn
rtsnuk rtsnku rtsknu rtskun rtusnk rtuskn rtunsk rtunks rtukns rtuksn rtnusk
rtnuks rtnsuk rtnsku rtnksu rtnkus rtkuns rtkusn rtknus rtknsu rtksnu rtksun
rstunk rstukn rstnuk rstnku rstknu rstkun rsutnk rsutkn rsuntk rsunkt rsuknt
rsuktn rsnutk rsnukt rsntuk rsntku rsnktu rsnkut rskunt rskutn rsknut rskntu
rsktnu rsktun rustnk rustkn rusntk rusnkt rusknt rusktn rutsnk rutskn rutnsk
rutnks rutkns rutksn runtsk runtks runstk runskt runkst runkts ruktns ruktsn
ruknts ruknst ruksnt rukstn rnsutk rnsukt rnstuk rnstku rnsktu rnskut rnustk
rnuskt rnutsk rnutks rnukts rnukst rntusk rntuks rntsuk rntsku rntksu rntkus
rnkuts rnkust rnktus rnktsu rnkstu rnksut rksunt rksutn rksnut rksntu rkstnu
rkstun rkusnt rkustn rkunst rkunts rkutns rkutsn rknust rknuts rknsut rknstu
rkntsu rkntus rktuns rktusn rktnus rktnsu rktsnu rktsun utrsnk utrskn utrnsk
utrnks utrkns utrksn utsrnk utsrkn utsnrk utsnkr utsknr utskrn utnsrk utnskr
utnrsk utnrks utnkrs utnksr utksnr utksrn utknsr utknrs utkrns utkrsn urtsnk
urtskn urtnsk urtnks urtkns urtksn urstnk urstkn ursntk ursnkt ursknt ursktn
urnstk urnskt urntsk urntks urnkts urnkst urksnt urkstn urknst urknts urktns
urktsn usrtnk usrtkn usrntk usrnkt usrknt usrktn ustrnk ustrkn ustnrk ustnkr
ustknr ustkrn usntrk usntkr usnrtk usnrkt usnkrt usnktr usktnr usktrn uskntr
usknrt uskrnt uskrtn unrstk unrskt unrtsk unrtks unrkts unrkst unsrtk unsrkt
unstrk unstkr unsktr unskrt untsrk untskr untrsk untrks untkrs untksr unkstr
unksrt unktsr unktrs unkrts unkrst ukrsnt ukrstn ukrnst ukrnts ukrtns ukrtsn
uksrnt uksrtn uksnrt uksntr ukstnr ukstrn uknsrt uknstr uknrst uknrts ukntrs
ukntsr uktsnr uktsrn uktnsr uktnrs uktrns uktrsn ntrusk ntruks ntrsuk ntrsku
ntrksu ntrkus ntursk nturks ntusrk ntuskr ntuksr ntukrs ntsurk ntsukr ntsruk
ntsrku ntskru ntskur ntkusr ntkurs ntksur ntksru ntkrsu ntkrus nrtusk nrtuks
nrtsuk nrtsku nrtksu nrtkus nrutsk nrutks nrustk nruskt nrukst nrukts nrsutk
nrsukt nrstuk nrstku nrsktu nrskut nrkust nrkuts nrksut nrkstu nrktsu nrktus
nurtsk nurtks nurstk nurskt nurkst nurkts nutrsk nutrks nutsrk nutskr nutksr
nutkrs nustrk nustkr nusrtk nusrkt nuskrt nusktr nuktsr nuktrs nukstr nuksrt
nukrst nukrts nsrutk nsrukt nsrtuk nsrtku nsrktu nsrkut nsurtk nsurkt nsutrk
nsutkr nsuktr nsukrt nsturk nstukr nstruk nstrku nstkru nstkur nskutr nskurt
nsktur nsktru nskrtu nskrut nkrust nkruts nkrsut nkrstu nkrtsu nkrtus nkurst
nkurts nkusrt nkustr nkutsr nkutrs nksurt nksutr nksrut nksrtu nkstru nkstur
nktusr nkturs nktsur nktsru nktrsu nktrus ktruns ktrusn ktrnus ktrnsu ktrsnu
ktrsun kturns ktursn ktunrs ktunsr ktusnr ktusrn ktnurs ktnusr ktnrus ktnrsu
ktnsru ktnsur ktsunr ktsurn ktsnur ktsnru ktsrnu ktsrun krtuns krtusn krtnus
krtnsu krtsnu krtsun krutns krutsn krunts krunst krusnt krustn krnuts krnust
krntus krntsu krnstu krnsut krsunt krsutn krsnut krsntu krstnu krstun kurtns
kurtsn kurnts kurnst kursnt kurstn kutrns kutrsn kutnrs kutnsr kutsnr kutsrn
kuntrs kuntsr kunrts kunrst kunsrt kunstr kustnr kustrn kusntr kusnrt kusrnt
kusrtn knruts knrust knrtus knrtsu knrstu knrsut knurts knurst knutrs knutsr
knustr knusrt knturs kntusr kntrus kntrsu kntsru kntsur knsutr knsurt knstur
knstru knsrtu knsrut ksrunt ksrutn ksrnut ksrntu ksrtnu ksrtun ksurnt ksurtn
ksunrt ksuntr ksutnr ksutrn ksnurt ksnutr ksnrut ksnrtu ksntru ksntur kstunr
ksturn kstnur kstnru kstrnu kstrun

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History of cryptography
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