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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: stadel
cipher variations:
tubefm uvcfgn vwdgho wxehip xyfijq
yzgjkr zahkls abilmt bcjmnu cdknov
delopw efmpqx fgnqry ghorsz hipsta
ijqtub jkruvc klsvwd lmtwxe mnuxyf
novyzg opwzah pqxabi qrybcj rszcdk

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: stadel
Cipher: hgzwvo

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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: stadel

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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: stadel
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: stadel
Cipher: fgnqry

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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: stadel
Cipher: 344411415113

Extended Methods:
Method #1

Plaintext: stadel
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 d e l 
3 4 1 4 5 1 
4 4 1 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: stadel
Cipher: sqetal

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Method #3

Plaintext: stadel
method variations:
tdqvan dqvant qvantd
vantdq antdqv ntdqva

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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: stadel

all 720 cipher variations:
stadel stadle staedl staeld staled stalde stdael stdale stdeal stdela stdlea
stdlae stedal stedla steadl steald stelad stelda stldea stldae stleda stlead
stlaed stlade satdel satdle satedl sateld satled satlde sadtel sadtle sadetl
sadelt sadlet sadlte saedtl saedlt saetdl saetld saeltd saeldt saldet saldte
saledt saletd salted saltde sdatel sdatle sdaetl sdaelt sdalet sdalte sdtael
sdtale sdteal sdtela sdtlea sdtlae sdetal sdetla sdeatl sdealt sdelat sdelta
sdltea sdltae sdleta sdleat sdlaet sdlate seadtl seadlt seatdl seatld sealtd
sealdt sedatl sedalt sedtal sedtla sedlta sedlat setdal setdla setadl setald
setlad setlda seldta seldat seltda seltad selatd seladt sladet sladte slaedt
slaetd slated slatde sldaet sldate sldeat sldeta sldtea sldtae sledat sledta
sleadt sleatd sletad sletda sltdea sltdae slteda sltead sltaed sltade tsadel
tsadle tsaedl tsaeld tsaled tsalde tsdael tsdale tsdeal tsdela tsdlea tsdlae
tsedal tsedla tseadl tseald tselad tselda tsldea tsldae tsleda tslead tslaed
tslade tasdel tasdle tasedl taseld tasled taslde tadsel tadsle tadesl tadels
tadles tadlse taedsl taedls taesdl taesld taelsd taelds taldes taldse taleds
talesd talsed talsde tdasel tdasle tdaesl tdaels tdales tdalse tdsael tdsale
tdseal tdsela tdslea tdslae tdesal tdesla tdeasl tdeals tdelas tdelsa tdlsea
tdlsae tdlesa tdleas tdlaes tdlase teadsl teadls teasdl teasld tealsd tealds
tedasl tedals tedsal tedsla tedlsa tedlas tesdal tesdla tesadl tesald teslad
teslda teldsa teldas telsda telsad telasd telads tlades tladse tlaeds tlaesd
tlased tlasde tldaes tldase tldeas tldesa tldsea tldsae tledas tledsa tleads
tleasd tlesad tlesda tlsdea tlsdae tlseda tlsead tlsaed tlsade atsdel atsdle
atsedl atseld atsled atslde atdsel atdsle atdesl atdels atdles atdlse atedsl
atedls atesdl atesld atelsd atelds atldes atldse atleds atlesd atlsed atlsde
astdel astdle astedl asteld astled astlde asdtel asdtle asdetl asdelt asdlet
asdlte asedtl asedlt asetdl asetld aseltd aseldt asldet asldte asledt asletd
aslted asltde adstel adstle adsetl adselt adslet adslte adtsel adtsle adtesl
adtels adtles adtlse adetsl adetls adestl adeslt adelst adelts adltes adltse
adlets adlest adlset adlste aesdtl aesdlt aestdl aestld aesltd aesldt aedstl
aedslt aedtsl aedtls aedlts aedlst aetdsl aetdls aetsdl aetsld aetlsd aetlds
aeldts aeldst aeltds aeltsd aelstd aelsdt alsdet alsdte alsedt alsetd alsted
alstde aldset aldste aldest aldets aldtes aldtse aledst aledts alesdt alestd
aletsd aletds altdes altdse alteds altesd altsed altsde dtasel dtasle dtaesl
dtaels dtales dtalse dtsael dtsale dtseal dtsela dtslea dtslae dtesal dtesla
dteasl dteals dtelas dtelsa dtlsea dtlsae dtlesa dtleas dtlaes dtlase datsel
datsle datesl datels datles datlse dastel dastle dasetl daselt daslet daslte
daestl daeslt daetsl daetls daelts daelst dalset dalste dalest dalets daltes
daltse dsatel dsatle dsaetl dsaelt dsalet dsalte dstael dstale dsteal dstela
dstlea dstlae dsetal dsetla dseatl dsealt dselat dselta dsltea dsltae dsleta
dsleat dslaet dslate deastl deaslt deatsl deatls dealts dealst desatl desalt
destal destla deslta deslat detsal detsla detasl detals detlas detlsa delsta
delsat deltsa deltas delats delast dlaset dlaste dlaest dlaets dlates dlatse
dlsaet dlsate dlseat dlseta dlstea dlstae dlesat dlesta dleast dleats dletas
dletsa dltsea dltsae dltesa dlteas dltaes dltase etadsl etadls etasdl etasld
etalsd etalds etdasl etdals etdsal etdsla etdlsa etdlas etsdal etsdla etsadl
etsald etslad etslda etldsa etldas etlsda etlsad etlasd etlads eatdsl eatdls
eatsdl eatsld eatlsd eatlds eadtsl eadtls eadstl eadslt eadlst eadlts easdtl
easdlt eastdl eastld easltd easldt ealdst ealdts ealsdt ealstd ealtsd ealtds
edatsl edatls edastl edaslt edalst edalts edtasl edtals edtsal edtsla edtlsa
edtlas edstal edstla edsatl edsalt edslat edslta edltsa edltas edlsta edlsat
edlast edlats esadtl esadlt esatdl esatld esaltd esaldt esdatl esdalt esdtal
esdtla esdlta esdlat estdal estdla estadl estald estlad estlda esldta esldat
esltda esltad eslatd esladt eladst eladts elasdt elastd elatsd elatds eldast
eldats eldsat eldsta eldtsa eldtas elsdat elsdta elsadt elsatd elstad elstda
eltdsa eltdas eltsda eltsad eltasd eltads ltades ltadse ltaeds ltaesd ltased
ltasde ltdaes ltdase ltdeas ltdesa ltdsea ltdsae ltedas ltedsa lteads lteasd
ltesad ltesda ltsdea ltsdae ltseda ltsead ltsaed ltsade latdes latdse lateds
latesd latsed latsde ladtes ladtse ladets ladest ladset ladste laedts laedst
laetds laetsd laestd laesdt lasdet lasdte lasedt lasetd lasted lastde ldates
ldatse ldaets ldaest ldaset ldaste ldtaes ldtase ldteas ldtesa ldtsea ldtsae
ldetas ldetsa ldeats ldeast ldesat ldesta ldstea ldstae ldseta ldseat ldsaet
ldsate leadts leadst leatds leatsd leastd leasdt ledats ledast ledtas ledtsa
ledsta ledsat letdas letdsa letads letasd letsad letsda lesdta lesdat lestda
lestad lesatd lesadt lsadet lsadte lsaedt lsaetd lsated lsatde lsdaet lsdate
lsdeat lsdeta lsdtea lsdtae lsedat lsedta lseadt lseatd lsetad lsetda lstdea
lstdae lsteda lstead lstaed lstade

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History of cryptography
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