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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: liketh
cipher variations:
mjlfui nkmgvj olnhwk pmoixl qnpjym
roqkzn sprlao tqsmbp urtncq vsuodr
wtvpes xuwqft yvxrgu zwyshv axztiw
byaujx czbvky dacwlz ebdxma fceynb
gdfzoc hegapd ifhbqe jgicrf khjdsg

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: liketh
Cipher: orpvgs

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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: liketh

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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: liketh
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: liketh
Cipher: yvxrgu

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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: liketh
Cipher: 134252514432

Extended Methods:
Method #1

Plaintext: liketh
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
l i k e t h 
1 4 5 5 4 3 
3 2 2 1 4 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: liketh
Cipher: qzohbi

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Method #3

Plaintext: liketh
method variations:
swwqob wwqobs wqobsw
qobsww obswwq bswwqo

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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: liketh

all 720 cipher variations:
liketh likeht likteh likthe likhte likhet liekth liekht lietkh liethk liehtk
liehkt litekh litehk litkeh litkhe lithke lithek lihetk lihekt lihtek lihtke
lihkte lihket lkieth lkieht lkiteh lkithe lkihte lkihet lkeith lkeiht lketih
lkethi lkehti lkehit lkteih lktehi lktieh lktihe lkthie lkthei lkheti lkheit
lkhtei lkhtie lkhite lkhiet lekith lekiht lektih lekthi lekhti lekhit leikth
leikht leitkh leithk leihtk leihkt letikh letihk letkih letkhi lethki lethik
lehitk lehikt lehtik lehtki lehkti lehkit ltkeih ltkehi ltkieh ltkihe ltkhie
ltkhei ltekih ltekhi lteikh lteihk ltehik ltehki ltiekh ltiehk ltikeh ltikhe
ltihke ltihek ltheik ltheki lthiek lthike lthkie lthkei lhketi lhkeit lhktei
lhktie lhkite lhkiet lhekti lhekit lhetki lhetik lheitk lheikt lhteki lhteik
lhtkei lhtkie lhtike lhtiek lhietk lhiekt lhitek lhitke lhikte lhiket ilketh
ilkeht ilkteh ilkthe ilkhte ilkhet ilekth ilekht iletkh ilethk ilehtk ilehkt
iltekh iltehk iltkeh iltkhe ilthke ilthek ilhetk ilhekt ilhtek ilhtke ilhkte
ilhket ikleth ikleht iklteh iklthe iklhte iklhet ikelth ikelht iketlh ikethl
ikehtl ikehlt iktelh iktehl iktleh iktlhe ikthle ikthel ikhetl ikhelt ikhtel
ikhtle ikhlte ikhlet ieklth ieklht iektlh iekthl iekhtl iekhlt ielkth ielkht
ieltkh ielthk ielhtk ielhkt ietlkh ietlhk ietklh ietkhl iethkl iethlk iehltk
iehlkt iehtlk iehtkl iehktl iehklt itkelh itkehl itkleh itklhe itkhle itkhel
iteklh itekhl itelkh itelhk itehlk itehkl itlekh itlehk itlkeh itlkhe itlhke
itlhek ithelk ithekl ithlek ithlke ithkle ithkel ihketl ihkelt ihktel ihktle
ihklte ihklet ihektl iheklt ihetkl ihetlk iheltk ihelkt ihtekl ihtelk ihtkel
ihtkle ihtlke ihtlek ihletk ihlekt ihltek ihltke ihlkte ihlket kileth kileht
kilteh kilthe kilhte kilhet kielth kielht kietlh kiethl kiehtl kiehlt kitelh
kitehl kitleh kitlhe kithle kithel kihetl kihelt kihtel kihtle kihlte kihlet
klieth klieht kliteh klithe klihte klihet kleith kleiht kletih klethi klehti
klehit klteih kltehi kltieh kltihe klthie klthei klheti klheit klhtei klhtie
klhite klhiet kelith keliht keltih kelthi kelhti kelhit keilth keilht keitlh
keithl keihtl keihlt ketilh ketihl ketlih ketlhi kethli kethil kehitl kehilt
kehtil kehtli kehlti kehlit ktleih ktlehi ktlieh ktlihe ktlhie ktlhei ktelih
ktelhi kteilh kteihl ktehil ktehli ktielh ktiehl ktileh ktilhe ktihle ktihel
ktheil ktheli kthiel kthile kthlie kthlei khleti khleit khltei khltie khlite
khliet khelti khelit khetli khetil kheitl kheilt khteli khteil khtlei khtlie
khtile khtiel khietl khielt khitel khitle khilte khilet eiklth eiklht eiktlh
eikthl eikhtl eikhlt eilkth eilkht eiltkh eilthk eilhtk eilhkt eitlkh eitlhk
eitklh eitkhl eithkl eithlk eihltk eihlkt eihtlk eihtkl eihktl eihklt ekilth
ekilht ekitlh ekithl ekihtl ekihlt eklith ekliht ekltih eklthi eklhti eklhit
ektlih ektlhi ektilh ektihl ekthil ekthli ekhlti ekhlit ekhtli ekhtil ekhitl
ekhilt elkith elkiht elktih elkthi elkhti elkhit elikth elikht elitkh elithk
elihtk elihkt eltikh eltihk eltkih eltkhi elthki elthik elhitk elhikt elhtik
elhtki elhkti elhkit etklih etklhi etkilh etkihl etkhil etkhli etlkih etlkhi
etlikh etlihk etlhik etlhki etilkh etilhk etiklh etikhl etihkl etihlk ethlik
ethlki ethilk ethikl ethkil ethkli ehklti ehklit ehktli ehktil ehkitl ehkilt
ehlkti ehlkit ehltki ehltik ehlitk ehlikt ehtlki ehtlik ehtkli ehtkil ehtikl
ehtilk ehiltk ehilkt ehitlk ehitkl ehiktl ehiklt tikelh tikehl tikleh tiklhe
tikhle tikhel tieklh tiekhl tielkh tielhk tiehlk tiehkl tilekh tilehk tilkeh
tilkhe tilhke tilhek tihelk tihekl tihlek tihlke tihkle tihkel tkielh tkiehl
tkileh tkilhe tkihle tkihel tkeilh tkeihl tkelih tkelhi tkehli tkehil tkleih
tklehi tklieh tklihe tklhie tklhei tkheli tkheil tkhlei tkhlie tkhile tkhiel
tekilh tekihl teklih teklhi tekhli tekhil teiklh teikhl teilkh teilhk teihlk
teihkl telikh telihk telkih telkhi telhki telhik tehilk tehikl tehlik tehlki
tehkli tehkil tlkeih tlkehi tlkieh tlkihe tlkhie tlkhei tlekih tlekhi tleikh
tleihk tlehik tlehki tliekh tliehk tlikeh tlikhe tlihke tlihek tlheik tlheki
tlhiek tlhike tlhkie tlhkei thkeli thkeil thklei thklie thkile thkiel thekli
thekil thelki thelik theilk theikl thleki thleik thlkei thlkie thlike thliek
thielk thiekl thilek thilke thikle thikel hiketl hikelt hiktel hiktle hiklte
hiklet hiektl hieklt hietkl hietlk hieltk hielkt hitekl hitelk hitkel hitkle
hitlke hitlek hiletk hilekt hiltek hiltke hilkte hilket hkietl hkielt hkitel
hkitle hkilte hkilet hkeitl hkeilt hketil hketli hkelti hkelit hkteil hkteli
hktiel hktile hktlie hktlei hkleti hkleit hkltei hkltie hklite hkliet hekitl
hekilt hektil hektli heklti heklit heiktl heiklt heitkl heitlk heiltk heilkt
hetikl hetilk hetkil hetkli hetlki hetlik helitk helikt heltik heltki helkti
helkit htkeil htkeli htkiel htkile htklie htklei htekil htekli hteikl hteilk
htelik htelki htiekl htielk htikel htikle htilke htilek htleik htleki htliek
htlike htlkie htlkei hlketi hlkeit hlktei hlktie hlkite hlkiet hlekti hlekit
hletki hletik hleitk hleikt hlteki hlteik hltkei hltkie hltike hltiek hlietk
hliekt hlitek hlitke hlikte hliket

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History of cryptography
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