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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: staver
cipher variations:
tubwfs uvcxgt vwdyhu wxeziv xyfajw
yzgbkx zahcly abidmz bcjena cdkfob
delgpc efmhqd fgnire ghojsf hipktg
ijqluh jkrmvi klsnwj lmtoxk mnupyl
novqzm opwran pqxsbo qrytcp rszudq

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: staver
Cipher: hgzevi

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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: staver

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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: staver
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: staver
Cipher: fgnire

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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: staver
Cipher: 344411155124

Extended Methods:
Method #1

Plaintext: staver
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 a v e r 
3 4 1 1 5 2 
4 4 1 5 1 4 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: staver
Cipher: saktvq

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Method #3

Plaintext: staver
method variations:
tdazfo dazfot azfotd
zfotda fotdaz otdazf

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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: staver

all 720 cipher variations:
staver stavre staevr staerv starev starve stvaer stvare stvear stvera stvrea
stvrae stevar stevra steavr stearv sterav sterva strvea strvae streva streav
straev strave satver satvre satevr saterv satrev satrve savter savtre savetr
savert savret savrte saevtr saevrt saetvr saetrv saertv saervt sarvet sarvte
sarevt saretv sartev sartve svater svatre svaetr svaert svaret svarte svtaer
svtare svtear svtera svtrea svtrae svetar svetra sveatr sveart sverat sverta
svrtea svrtae svreta svreat svraet svrate seavtr seavrt seatvr seatrv seartv
searvt sevatr sevart sevtar sevtra sevrta sevrat setvar setvra setavr setarv
setrav setrva servta servat sertva sertav seratv seravt sravet sravte sraevt
sraetv sratev sratve srvaet srvate srveat srveta srvtea srvtae srevat srevta
sreavt sreatv sretav sretva srtvea srtvae srteva srteav srtaev srtave tsaver
tsavre tsaevr tsaerv tsarev tsarve tsvaer tsvare tsvear tsvera tsvrea tsvrae
tsevar tsevra tseavr tsearv tserav tserva tsrvea tsrvae tsreva tsreav tsraev
tsrave tasver tasvre tasevr taserv tasrev tasrve tavser tavsre tavesr tavers
tavres tavrse taevsr taevrs taesvr taesrv taersv taervs tarves tarvse tarevs
taresv tarsev tarsve tvaser tvasre tvaesr tvaers tvares tvarse tvsaer tvsare
tvsear tvsera tvsrea tvsrae tvesar tvesra tveasr tvears tveras tversa tvrsea
tvrsae tvresa tvreas tvraes tvrase teavsr teavrs teasvr teasrv tearsv tearvs
tevasr tevars tevsar tevsra tevrsa tevras tesvar tesvra tesavr tesarv tesrav
tesrva tervsa tervas tersva tersav terasv teravs traves travse traevs traesv
trasev trasve trvaes trvase trveas trvesa trvsea trvsae trevas trevsa treavs
treasv tresav tresva trsvea trsvae trseva trseav trsaev trsave atsver atsvre
atsevr atserv atsrev atsrve atvser atvsre atvesr atvers atvres atvrse atevsr
atevrs atesvr atesrv atersv atervs atrves atrvse atrevs atresv atrsev atrsve
astver astvre astevr asterv astrev astrve asvter asvtre asvetr asvert asvret
asvrte asevtr asevrt asetvr asetrv asertv aservt asrvet asrvte asrevt asretv
asrtev asrtve avster avstre avsetr avsert avsret avsrte avtser avtsre avtesr
avters avtres avtrse avetsr avetrs avestr avesrt averst averts avrtes avrtse
avrets avrest avrset avrste aesvtr aesvrt aestvr aestrv aesrtv aesrvt aevstr
aevsrt aevtsr aevtrs aevrts aevrst aetvsr aetvrs aetsvr aetsrv aetrsv aetrvs
aervts aervst aertvs aertsv aerstv aersvt arsvet arsvte arsevt arsetv arstev
arstve arvset arvste arvest arvets arvtes arvtse arevst arevts aresvt arestv
aretsv aretvs artves artvse artevs artesv artsev artsve vtaser vtasre vtaesr
vtaers vtares vtarse vtsaer vtsare vtsear vtsera vtsrea vtsrae vtesar vtesra
vteasr vtears vteras vtersa vtrsea vtrsae vtresa vtreas vtraes vtrase vatser
vatsre vatesr vaters vatres vatrse vaster vastre vasetr vasert vasret vasrte
vaestr vaesrt vaetsr vaetrs vaerts vaerst varset varste varest varets vartes
vartse vsater vsatre vsaetr vsaert vsaret vsarte vstaer vstare vstear vstera
vstrea vstrae vsetar vsetra vseatr vseart vserat vserta vsrtea vsrtae vsreta
vsreat vsraet vsrate veastr veasrt veatsr veatrs vearts vearst vesatr vesart
vestar vestra vesrta vesrat vetsar vetsra vetasr vetars vetras vetrsa versta
versat vertsa vertas verats verast vraset vraste vraest vraets vrates vratse
vrsaet vrsate vrseat vrseta vrstea vrstae vresat vresta vreast vreats vretas
vretsa vrtsea vrtsae vrtesa vrteas vrtaes vrtase etavsr etavrs etasvr etasrv
etarsv etarvs etvasr etvars etvsar etvsra etvrsa etvras etsvar etsvra etsavr
etsarv etsrav etsrva etrvsa etrvas etrsva etrsav etrasv etravs eatvsr eatvrs
eatsvr eatsrv eatrsv eatrvs eavtsr eavtrs eavstr eavsrt eavrst eavrts easvtr
easvrt eastvr eastrv easrtv easrvt earvst earvts earsvt earstv eartsv eartvs
evatsr evatrs evastr evasrt evarst evarts evtasr evtars evtsar evtsra evtrsa
evtras evstar evstra evsatr evsart evsrat evsrta evrtsa evrtas evrsta evrsat
evrast evrats esavtr esavrt esatvr esatrv esartv esarvt esvatr esvart esvtar
esvtra esvrta esvrat estvar estvra estavr estarv estrav estrva esrvta esrvat
esrtva esrtav esratv esravt eravst eravts erasvt erastv eratsv eratvs ervast
ervats ervsat ervsta ervtsa ervtas ersvat ersvta ersavt ersatv erstav erstva
ertvsa ertvas ertsva ertsav ertasv ertavs rtaves rtavse rtaevs rtaesv rtasev
rtasve rtvaes rtvase rtveas rtvesa rtvsea rtvsae rtevas rtevsa rteavs rteasv
rtesav rtesva rtsvea rtsvae rtseva rtseav rtsaev rtsave ratves ratvse ratevs
ratesv ratsev ratsve ravtes ravtse ravets ravest ravset ravste raevts raevst
raetvs raetsv raestv raesvt rasvet rasvte rasevt rasetv rastev rastve rvates
rvatse rvaets rvaest rvaset rvaste rvtaes rvtase rvteas rvtesa rvtsea rvtsae
rvetas rvetsa rveats rveast rvesat rvesta rvstea rvstae rvseta rvseat rvsaet
rvsate reavts reavst reatvs reatsv reastv reasvt revats revast revtas revtsa
revsta revsat retvas retvsa retavs retasv retsav retsva resvta resvat restva
restav resatv resavt rsavet rsavte rsaevt rsaetv rsatev rsatve rsvaet rsvate
rsveat rsveta rsvtea rsvtae rsevat rsevta rseavt rseatv rsetav rsetva rstvea
rstvae rsteva rsteav rstaev rstave

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History of cryptography
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