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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: hpcuoa
cipher variations:
iqdvpb jrewqc ksfxrd ltgyse muhztf
nviaug owjbvh pxkcwi qyldxj rzmeyk
sanfzl tbogam ucphbn vdqico werjdp
xfskeq ygtlfr zhumgs aivnht bjwoiu
ckxpjv dlyqkw emzrlx fnasmy gobtnz

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: hpcuoa
Cipher: skxflz

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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: hpcuoa

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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: hpcuoa
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: hpcuoa
Cipher: ucphbn

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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: hpcuoa
Cipher: 325331544311

Extended Methods:
Method #1

Plaintext: hpcuoa
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
h p c u o a 
3 5 3 5 4 1 
2 3 1 4 3 1 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: hpcuoa
Cipher: xxdmqc

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Method #3

Plaintext: hpcuoa
method variations:
wnvtcl nvtclw vtclwn
tclwnv clwnvt lwnvtc

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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: hpcuoa

all 720 cipher variations:
hpcuoa hpcuao hpcoua hpcoau hpcaou hpcauo hpucoa hpucao hpuoca hpuoac hpuaoc
hpuaco hpouca hpouac hpocua hpocau hpoacu hpoauc hpauoc hpauco hpaouc hpaocu
hpacou hpacuo hcpuoa hcpuao hcpoua hcpoau hcpaou hcpauo hcupoa hcupao hcuopa
hcuoap hcuaop hcuapo hcoupa hcouap hcopua hcopau hcoapu hcoaup hcauop hcaupo
hcaoup hcaopu hcapou hcapuo hucpoa hucpao hucopa hucoap hucaop hucapo hupcoa
hupcao hupoca hupoac hupaoc hupaco huopca huopac huocpa huocap huoacp huoapc
huapoc huapco huaopc huaocp huacop huacpo hocupa hocuap hocpua hocpau hocapu
hocaup houcpa houcap houpca houpac houapc houacp hopuca hopuac hopcua hopcau
hopacu hopauc hoaupc hoaucp hoapuc hoapcu hoacpu hoacup hacuop hacupo hacoup
hacopu hacpou hacpuo haucop haucpo hauocp hauopc haupoc haupco haoucp haoupc
haocup haocpu haopcu haopuc hapuoc hapuco hapouc hapocu hapcou hapcuo phcuoa
phcuao phcoua phcoau phcaou phcauo phucoa phucao phuoca phuoac phuaoc phuaco
phouca phouac phocua phocau phoacu phoauc phauoc phauco phaouc phaocu phacou
phacuo pchuoa pchuao pchoua pchoau pchaou pchauo pcuhoa pcuhao pcuoha pcuoah
pcuaoh pcuaho pcouha pcouah pcohua pcohau pcoahu pcoauh pcauoh pcauho pcaouh
pcaohu pcahou pcahuo puchoa puchao pucoha pucoah pucaoh pucaho puhcoa puhcao
puhoca puhoac puhaoc puhaco puohca puohac puocha puocah puoach puoahc puahoc
puahco puaohc puaoch puacoh puacho pocuha pocuah pochua pochau pocahu pocauh
poucha poucah pouhca pouhac pouahc pouach pohuca pohuac pohcua pohcau pohacu
pohauc poauhc poauch poahuc poahcu poachu poacuh pacuoh pacuho pacouh pacohu
pachou pachuo paucoh paucho pauoch pauohc pauhoc pauhco paouch paouhc paocuh
paochu paohcu paohuc pahuoc pahuco pahouc pahocu pahcou pahcuo cphuoa cphuao
cphoua cphoau cphaou cphauo cpuhoa cpuhao cpuoha cpuoah cpuaoh cpuaho cpouha
cpouah cpohua cpohau cpoahu cpoauh cpauoh cpauho cpaouh cpaohu cpahou cpahuo
chpuoa chpuao chpoua chpoau chpaou chpauo chupoa chupao chuopa chuoap chuaop
chuapo choupa chouap chopua chopau choapu choaup chauop chaupo chaoup chaopu
chapou chapuo cuhpoa cuhpao cuhopa cuhoap cuhaop cuhapo cuphoa cuphao cupoha
cupoah cupaoh cupaho cuopha cuopah cuohpa cuohap cuoahp cuoaph cuapoh cuapho
cuaoph cuaohp cuahop cuahpo cohupa cohuap cohpua cohpau cohapu cohaup couhpa
couhap coupha coupah couaph couahp copuha copuah cophua cophau copahu copauh
coauph coauhp coapuh coaphu coahpu coahup cahuop cahupo cahoup cahopu cahpou
cahpuo cauhop cauhpo cauohp cauoph caupoh caupho caouhp caouph caohup caohpu
caophu caopuh capuoh capuho capouh capohu caphou caphuo upchoa upchao upcoha
upcoah upcaoh upcaho uphcoa uphcao uphoca uphoac uphaoc uphaco upohca upohac
upocha upocah upoach upoahc upahoc upahco upaohc upaoch upacoh upacho ucphoa
ucphao ucpoha ucpoah ucpaoh ucpaho uchpoa uchpao uchopa uchoap uchaop uchapo
ucohpa ucohap ucopha ucopah ucoaph ucoahp ucahop ucahpo ucaohp ucaoph ucapoh
ucapho uhcpoa uhcpao uhcopa uhcoap uhcaop uhcapo uhpcoa uhpcao uhpoca uhpoac
uhpaoc uhpaco uhopca uhopac uhocpa uhocap uhoacp uhoapc uhapoc uhapco uhaopc
uhaocp uhacop uhacpo uochpa uochap uocpha uocpah uocaph uocahp uohcpa uohcap
uohpca uohpac uohapc uohacp uophca uophac uopcha uopcah uopach uopahc uoahpc
uoahcp uoaphc uoapch uoacph uoachp uachop uachpo uacohp uacoph uacpoh uacpho
uahcop uahcpo uahocp uahopc uahpoc uahpco uaohcp uaohpc uaochp uaocph uaopch
uaophc uaphoc uaphco uapohc uapoch uapcoh uapcho opcuha opcuah opchua opchau
opcahu opcauh opucha opucah opuhca opuhac opuahc opuach ophuca ophuac ophcua
ophcau ophacu ophauc opauhc opauch opahuc opahcu opachu opacuh ocpuha ocpuah
ocphua ocphau ocpahu ocpauh ocupha ocupah ocuhpa ocuhap ocuahp ocuaph ochupa
ochuap ochpua ochpau ochapu ochaup ocauhp ocauph ocahup ocahpu ocaphu ocapuh
oucpha oucpah ouchpa ouchap oucahp oucaph oupcha oupcah ouphca ouphac oupahc
oupach ouhpca ouhpac ouhcpa ouhcap ouhacp ouhapc ouaphc ouapch ouahpc ouahcp
ouachp ouacph ohcupa ohcuap ohcpua ohcpau ohcapu ohcaup ohucpa ohucap ohupca
ohupac ohuapc ohuacp ohpuca ohpuac ohpcua ohpcau ohpacu ohpauc ohaupc ohaucp
ohapuc ohapcu ohacpu ohacup oacuhp oacuph oachup oachpu oacphu oacpuh oauchp
oaucph oauhcp oauhpc oauphc oaupch oahucp oahupc oahcup oahcpu oahpcu oahpuc
oapuhc oapuch oaphuc oaphcu oapchu oapcuh apcuoh apcuho apcouh apcohu apchou
apchuo apucoh apucho apuoch apuohc apuhoc apuhco apouch apouhc apocuh apochu
apohcu apohuc aphuoc aphuco aphouc aphocu aphcou aphcuo acpuoh acpuho acpouh
acpohu acphou acphuo acupoh acupho acuoph acuohp acuhop acuhpo acouph acouhp
acopuh acophu acohpu acohup achuop achupo achoup achopu achpou achpuo aucpoh
aucpho aucoph aucohp auchop auchpo aupcoh aupcho aupoch aupohc auphoc auphco
auopch auophc auocph auochp auohcp auohpc auhpoc auhpco auhopc auhocp auhcop
auhcpo aocuph aocuhp aocpuh aocphu aochpu aochup aoucph aouchp aoupch aouphc
aouhpc aouhcp aopuch aopuhc aopcuh aopchu aophcu aophuc aohupc aohucp aohpuc
aohpcu aohcpu aohcup ahcuop ahcupo ahcoup ahcopu ahcpou ahcpuo ahucop ahucpo
ahuocp ahuopc ahupoc ahupco ahoucp ahoupc ahocup ahocpu ahopcu ahopuc ahpuoc
ahpuco ahpouc ahpocu ahpcou ahpcuo

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History of cryptography
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