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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: voicer
cipher variations:
wpjdfs xqkegt yrlfhu zsmgiv atnhjw
buoikx cvpjly dwqkmz exrlna fysmob
gztnpc hauoqd ibvpre jcwqsf kdxrtg
leysuh mfztvi ngauwj ohbvxk picwyl
qjdxzm rkeyan slfzbo tmgacp unhbdq

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: voicer
Cipher: elrxvi

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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: voicer

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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: voicer
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: voicer
Cipher: ibvpre

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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: voicer
Cipher: 154342315124

Extended Methods:
Method #1

Plaintext: voicer
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
v o i c e r 
1 4 4 3 5 2 
5 3 2 1 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: voicer
Cipher: qokpbq

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Method #3

Plaintext: voicer
method variations:
usmvfd smvfdu mvfdus
vfdusm fdusmv dusmvf

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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: voicer

all 720 cipher variations:
voicer voicre voiecr voierc voirec voirce vocier vocire voceir voceri vocrei
vocrie voecir voecri voeicr voeirc voeric voerci vorcei vorcie voreci voreic
voriec vorice viocer viocre vioecr vioerc viorec viorce vicoer vicore viceor
vicero vicreo vicroe viecor viecro vieocr vieorc vieroc vierco virceo vircoe
vireco vireoc viroec viroce vcioer vciore vcieor vciero vcireo vciroe vcoier
vcoire vcoeir vcoeri vcorei vcorie vceoir vceori vceior vceiro vcerio vceroi
vcroei vcroie vcreoi vcreio vcrieo vcrioe veicor veicro veiocr veiorc veiroc
veirco vecior veciro vecoir vecori vecroi vecrio veocir veocri veoicr veoirc
veoric veorci vercoi vercio veroci veroic verioc verico vriceo vricoe vrieco
vrieoc vrioec vrioce vrcieo vrcioe vrceio vrceoi vrcoei vrcoie vrecio vrecoi
vreico vreioc vreoic vreoci vrocei vrocie vroeci vroeic vroiec vroice ovicer
ovicre oviecr ovierc ovirec ovirce ovcier ovcire ovceir ovceri ovcrei ovcrie
ovecir ovecri oveicr oveirc overic overci ovrcei ovrcie ovreci ovreic ovriec
ovrice oivcer oivcre oivecr oiverc oivrec oivrce oicver oicvre oicevr oicerv
oicrev oicrve oiecvr oiecrv oievcr oievrc oiervc oiercv oircev oircve oirecv
oirevc oirvec oirvce ociver ocivre ocievr ocierv ocirev ocirve ocvier ocvire
ocveir ocveri ocvrei ocvrie ocevir ocevri oceivr oceirv oceriv ocervi ocrvei
ocrvie ocrevi ocreiv ocriev ocrive oeicvr oeicrv oeivcr oeivrc oeirvc oeircv
oecivr oecirv oecvir oecvri oecrvi oecriv oevcir oevcri oevicr oevirc oevric
oevrci oercvi oerciv oervci oervic oerivc oericv oricev oricve oriecv orievc
orivec orivce orciev orcive orceiv orcevi orcvei orcvie oreciv orecvi oreicv
oreivc orevic orevci orvcei orvcie orveci orveic orviec orvice iovcer iovcre
iovecr ioverc iovrec iovrce iocver iocvre iocevr iocerv iocrev iocrve ioecvr
ioecrv ioevcr ioevrc ioervc ioercv iorcev iorcve iorecv iorevc iorvec iorvce
ivocer ivocre ivoecr ivoerc ivorec ivorce ivcoer ivcore ivceor ivcero ivcreo
ivcroe ivecor ivecro iveocr iveorc iveroc iverco ivrceo ivrcoe ivreco ivreoc
ivroec ivroce icvoer icvore icveor icvero icvreo icvroe icover icovre icoevr
icoerv icorev icorve iceovr iceorv icevor icevro icervo icerov icroev icrove
icreov icrevo icrveo icrvoe ievcor ievcro ievocr ievorc ievroc ievrco iecvor
iecvro iecovr iecorv iecrov iecrvo ieocvr ieocrv ieovcr ieovrc ieorvc ieorcv
iercov iercvo ierocv ierovc iervoc iervco irvceo irvcoe irveco irveoc irvoec
irvoce ircveo ircvoe ircevo irceov ircoev ircove irecvo irecov irevco irevoc
ireovc ireocv irocev irocve iroecv iroevc irovec irovce coiver coivre coievr
coierv coirev coirve covier covire coveir coveri covrei covrie coevir coevri
coeivr coeirv coeriv coervi corvei corvie corevi coreiv coriev corive ciover
ciovre cioevr cioerv ciorev ciorve civoer civore civeor civero civreo civroe
cievor cievro cieovr cieorv cierov ciervo cirveo cirvoe cirevo cireov ciroev
cirove cvioer cviore cvieor cviero cvireo cviroe cvoier cvoire cvoeir cvoeri
cvorei cvorie cveoir cveori cveior cveiro cverio cveroi cvroei cvroie cvreoi
cvreio cvrieo cvrioe ceivor ceivro ceiovr ceiorv ceirov ceirvo cevior ceviro
cevoir cevori cevroi cevrio ceovir ceovri ceoivr ceoirv ceoriv ceorvi cervoi
cervio cerovi ceroiv ceriov cerivo criveo crivoe crievo crieov crioev criove
crvieo crvioe crveio crveoi crvoei crvoie crevio crevoi creivo creiov creoiv
creovi crovei crovie croevi croeiv croiev croive eoicvr eoicrv eoivcr eoivrc
eoirvc eoircv eocivr eocirv eocvir eocvri eocrvi eocriv eovcir eovcri eovicr
eovirc eovric eovrci eorcvi eorciv eorvci eorvic eorivc eoricv eiocvr eiocrv
eiovcr eiovrc eiorvc eiorcv eicovr eicorv eicvor eicvro eicrvo eicrov eivcor
eivcro eivocr eivorc eivroc eivrco eircvo eircov eirvco eirvoc eirovc eirocv
eciovr eciorv ecivor ecivro ecirvo ecirov ecoivr ecoirv ecovir ecovri ecorvi
ecoriv ecvoir ecvori ecvior ecviro ecvrio ecvroi ecrovi ecroiv ecrvoi ecrvio
ecrivo ecriov evicor evicro eviocr eviorc eviroc evirco evcior evciro evcoir
evcori evcroi evcrio evocir evocri evoicr evoirc evoric evorci evrcoi evrcio
evroci evroic evrioc evrico ericvo ericov erivco erivoc eriovc eriocv ercivo
erciov ercvio ercvoi ercovi ercoiv ervcio ervcoi ervico ervioc ervoic ervoci
erocvi erociv erovci erovic eroivc eroicv roicev roicve roiecv roievc roivec
roivce rociev rocive roceiv rocevi rocvei rocvie roeciv roecvi roeicv roeivc
roevic roevci rovcei rovcie roveci roveic roviec rovice riocev riocve rioecv
rioevc riovec riovce ricoev ricove riceov ricevo ricveo ricvoe riecov riecvo
rieocv rieovc rievoc rievco rivceo rivcoe riveco riveoc rivoec rivoce rcioev
rciove rcieov rcievo rciveo rcivoe rcoiev rcoive rcoeiv rcoevi rcovei rcovie
rceoiv rceovi rceiov rceivo rcevio rcevoi rcvoei rcvoie rcveoi rcveio rcvieo
rcvioe reicov reicvo reiocv reiovc reivoc reivco reciov recivo recoiv recovi
recvoi recvio reociv reocvi reoicv reoivc reovic reovci revcoi revcio revoci
revoic revioc revico rviceo rvicoe rvieco rvieoc rvioec rvioce rvcieo rvcioe
rvceio rvceoi rvcoei rvcoie rvecio rvecoi rveico rveioc rveoic rveoci rvocei
rvocie rvoeci rvoeic rvoiec rvoice

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History of cryptography
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