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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: pravus
cipher variations:
qsbwvt rtcxwu sudyxv tvezyw uwfazx
vxgbay wyhcbz xzidca yajedb zbkfec
aclgfd bdmhge cenihf dfojig egpkjh
fhqlki girmlj hjsnmk iktonl jlupom
kmvqpn lnwrqo moxsrp npytsq oqzutr

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: pravus
Cipher: kizefh

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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: pravus

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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: pravus
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: pravus
Cipher: cenihf

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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: pravus
Cipher: 532411155434

Extended Methods:
Method #1

Plaintext: pravus
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
p r a v u s 
5 2 1 1 5 3 
3 4 1 5 4 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: pravus
Cipher: kapsvt

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Method #3

Plaintext: pravus
method variations:
hdazoy dazoyh azoyhd
zoyhda oyhdaz yhdazo

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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: pravus

all 720 cipher variations:
pravus pravsu prauvs prausv prasuv prasvu prvaus prvasu prvuas prvusa prvsua
prvsau pruvas pruvsa pruavs pruasv prusav prusva prsvua prsvau prsuva prsuav
prsauv prsavu parvus parvsu paruvs parusv parsuv parsvu pavrus pavrsu pavurs
pavusr pavsur pavsru pauvrs pauvsr paurvs paursv pausrv pausvr pasvur pasvru
pasuvr pasurv pasruv pasrvu pvarus pvarsu pvaurs pvausr pvasur pvasru pvraus
pvrasu pvruas pvrusa pvrsua pvrsau pvuras pvursa pvuars pvuasr pvusar pvusra
pvsrua pvsrau pvsura pvsuar pvsaur pvsaru puavrs puavsr puarvs puarsv puasrv
puasvr puvars puvasr puvras puvrsa puvsra puvsar purvas purvsa puravs purasv
pursav pursva pusvra pusvar pusrva pusrav pusarv pusavr psavur psavru psauvr
psaurv psaruv psarvu psvaur psvaru psvuar psvura psvrua psvrau psuvar psuvra
psuavr psuarv psurav psurva psrvua psrvau psruva psruav psrauv psravu rpavus
rpavsu rpauvs rpausv rpasuv rpasvu rpvaus rpvasu rpvuas rpvusa rpvsua rpvsau
rpuvas rpuvsa rpuavs rpuasv rpusav rpusva rpsvua rpsvau rpsuva rpsuav rpsauv
rpsavu rapvus rapvsu rapuvs rapusv rapsuv rapsvu ravpus ravpsu ravups ravusp
ravsup ravspu rauvps rauvsp raupvs raupsv rauspv rausvp rasvup rasvpu rasuvp
rasupv raspuv raspvu rvapus rvapsu rvaups rvausp rvasup rvaspu rvpaus rvpasu
rvpuas rvpusa rvpsua rvpsau rvupas rvupsa rvuaps rvuasp rvusap rvuspa rvspua
rvspau rvsupa rvsuap rvsaup rvsapu ruavps ruavsp ruapvs ruapsv ruaspv ruasvp
ruvaps ruvasp ruvpas ruvpsa ruvspa ruvsap rupvas rupvsa rupavs rupasv rupsav
rupsva rusvpa rusvap ruspva ruspav rusapv rusavp rsavup rsavpu rsauvp rsaupv
rsapuv rsapvu rsvaup rsvapu rsvuap rsvupa rsvpua rsvpau rsuvap rsuvpa rsuavp
rsuapv rsupav rsupva rspvua rspvau rspuva rspuav rspauv rspavu arpvus arpvsu
arpuvs arpusv arpsuv arpsvu arvpus arvpsu arvups arvusp arvsup arvspu aruvps
aruvsp arupvs arupsv aruspv arusvp arsvup arsvpu arsuvp arsupv arspuv arspvu
aprvus aprvsu apruvs aprusv aprsuv aprsvu apvrus apvrsu apvurs apvusr apvsur
apvsru apuvrs apuvsr apurvs apursv apusrv apusvr apsvur apsvru apsuvr apsurv
apsruv apsrvu avprus avprsu avpurs avpusr avpsur avpsru avrpus avrpsu avrups
avrusp avrsup avrspu avurps avursp avuprs avupsr avuspr avusrp avsrup avsrpu
avsurp avsupr avspur avspru aupvrs aupvsr auprvs auprsv aupsrv aupsvr auvprs
auvpsr auvrps auvrsp auvsrp auvspr aurvps aurvsp aurpvs aurpsv aurspv aursvp
ausvrp ausvpr ausrvp ausrpv ausprv auspvr aspvur aspvru aspuvr aspurv aspruv
asprvu asvpur asvpru asvupr asvurp asvrup asvrpu asuvpr asuvrp asupvr asuprv
asurpv asurvp asrvup asrvpu asruvp asrupv asrpuv asrpvu vrapus vrapsu vraups
vrausp vrasup vraspu vrpaus vrpasu vrpuas vrpusa vrpsua vrpsau vrupas vrupsa
vruaps vruasp vrusap vruspa vrspua vrspau vrsupa vrsuap vrsaup vrsapu varpus
varpsu varups varusp varsup varspu vaprus vaprsu vapurs vapusr vapsur vapsru
vauprs vaupsr vaurps vaursp vausrp vauspr vaspur vaspru vasupr vasurp vasrup
vasrpu vparus vparsu vpaurs vpausr vpasur vpasru vpraus vprasu vpruas vprusa
vprsua vprsau vpuras vpursa vpuars vpuasr vpusar vpusra vpsrua vpsrau vpsura
vpsuar vpsaur vpsaru vuaprs vuapsr vuarps vuarsp vuasrp vuaspr vupars vupasr
vupras vuprsa vupsra vupsar vurpas vurpsa vuraps vurasp vursap vurspa vuspra
vuspar vusrpa vusrap vusarp vusapr vsapur vsapru vsaupr vsaurp vsarup vsarpu
vspaur vsparu vspuar vspura vsprua vsprau vsupar vsupra vsuapr vsuarp vsurap
vsurpa vsrpua vsrpau vsrupa vsruap vsraup vsrapu uravps uravsp urapvs urapsv
uraspv urasvp urvaps urvasp urvpas urvpsa urvspa urvsap urpvas urpvsa urpavs
urpasv urpsav urpsva ursvpa ursvap urspva urspav ursapv ursavp uarvps uarvsp
uarpvs uarpsv uarspv uarsvp uavrps uavrsp uavprs uavpsr uavspr uavsrp uapvrs
uapvsr uaprvs uaprsv uapsrv uapsvr uasvpr uasvrp uaspvr uasprv uasrpv uasrvp
uvarps uvarsp uvaprs uvapsr uvaspr uvasrp uvraps uvrasp uvrpas uvrpsa uvrspa
uvrsap uvpras uvprsa uvpars uvpasr uvpsar uvpsra uvsrpa uvsrap uvspra uvspar
uvsapr uvsarp upavrs upavsr uparvs uparsv upasrv upasvr upvars upvasr upvras
upvrsa upvsra upvsar uprvas uprvsa upravs uprasv uprsav uprsva upsvra upsvar
upsrva upsrav upsarv upsavr usavpr usavrp usapvr usaprv usarpv usarvp usvapr
usvarp usvpar usvpra usvrpa usvrap uspvar uspvra uspavr usparv usprav usprva
usrvpa usrvap usrpva usrpav usrapv usravp sravup sravpu srauvp sraupv srapuv
srapvu srvaup srvapu srvuap srvupa srvpua srvpau sruvap sruvpa sruavp sruapv
srupav srupva srpvua srpvau srpuva srpuav srpauv srpavu sarvup sarvpu saruvp
sarupv sarpuv sarpvu savrup savrpu savurp savupr savpur savpru sauvrp sauvpr
saurvp saurpv sauprv saupvr sapvur sapvru sapuvr sapurv sapruv saprvu svarup
svarpu svaurp svaupr svapur svapru svraup svrapu svruap svrupa svrpua svrpau
svurap svurpa svuarp svuapr svupar svupra svprua svprau svpura svpuar svpaur
svparu suavrp suavpr suarvp suarpv suaprv suapvr suvarp suvapr suvrap suvrpa
suvpra suvpar survap survpa suravp surapv surpav surpva supvra supvar suprva
suprav suparv supavr spavur spavru spauvr spaurv sparuv sparvu spvaur spvaru
spvuar spvura spvrua spvrau spuvar spuvra spuavr spuarv spurav spurva sprvua
sprvau spruva spruav sprauv spravu

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History of cryptography
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