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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: kopsha
cipher variations:
lpqtib mqrujc nrsvkd ostwle ptuxmf
quvyng rvwzoh swxapi txybqj uyzcrk
vzadsl wabetm xbcfun ycdgvo zdehwp
aefixq bfgjyr cghkzs dhilat eijmbu
fjkncv gklodw hlmpex imnqfy jnorgz

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: kopsha
Cipher: plkhsz

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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: kopsha

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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: kopsha
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: kopsha
Cipher: xbcfun

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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: kopsha
Cipher: 524353343211

Extended Methods:
Method #1

Plaintext: kopsha
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
k o p s h a 
5 4 5 3 3 1 
2 3 3 4 2 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: kopsha
Cipher: upcmsb

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Method #3

Plaintext: kopsha
method variations:
rxnobv xnobvr nobvrx
obvrxn bvrxno vrxnob

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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: kopsha

all 720 cipher variations:
kopsha kopsah kophsa kophas kopahs kopash kospha kospah koshpa koshap kosahp
kosaph kohspa kohsap kohpsa kohpas kohaps kohasp koashp koasph koahsp koahps
koaphs koapsh kposha kposah kpohsa kpohas kpoahs kpoash kpsoha kpsoah kpshoa
kpshao kpsaho kpsaoh kphsoa kphsao kphosa kphoas kphaos kphaso kpasho kpasoh
kpahso kpahos kpaohs kpaosh kspoha kspoah ksphoa ksphao kspaho kspaoh ksopha
ksopah ksohpa ksohap ksoahp ksoaph kshopa kshoap kshpoa kshpao kshapo kshaop
ksaohp ksaoph ksahop ksahpo ksapho ksapoh khpsoa khpsao khposa khpoas khpaos
khpaso khspoa khspao khsopa khsoap khsaop khsapo khospa khosap khopsa khopas
khoaps khoasp khasop khaspo khaosp khaops khapos khapso kapsho kapsoh kaphso
kaphos kapohs kaposh kaspho kaspoh kashpo kashop kasohp kasoph kahspo kahsop
kahpso kahpos kahops kahosp kaoshp kaosph kaohsp kaohps kaophs kaopsh okpsha
okpsah okphsa okphas okpahs okpash okspha okspah okshpa okshap oksahp oksaph
okhspa okhsap okhpsa okhpas okhaps okhasp okashp okasph okahsp okahps okaphs
okapsh opksha opksah opkhsa opkhas opkahs opkash opskha opskah opshka opshak
opsahk opsakh ophska ophsak ophksa ophkas ophaks ophask opashk opaskh opahsk
opahks opakhs opaksh ospkha ospkah osphka osphak ospahk ospakh oskpha oskpah
oskhpa oskhap oskahp oskaph oshkpa oshkap oshpka oshpak oshapk oshakp osakhp
osakph osahkp osahpk osaphk osapkh ohpska ohpsak ohpksa ohpkas ohpaks ohpask
ohspka ohspak ohskpa ohskap ohsakp ohsapk ohkspa ohksap ohkpsa ohkpas ohkaps
ohkasp ohaskp ohaspk ohaksp ohakps ohapks ohapsk oapshk oapskh oaphsk oaphks
oapkhs oapksh oasphk oaspkh oashpk oashkp oaskhp oaskph oahspk oahskp oahpsk
oahpks oahkps oahksp oakshp oaksph oakhsp oakhps oakphs oakpsh poksha poksah
pokhsa pokhas pokahs pokash poskha poskah poshka poshak posahk posakh pohska
pohsak pohksa pohkas pohaks pohask poashk poaskh poahsk poahks poakhs poaksh
pkosha pkosah pkohsa pkohas pkoahs pkoash pksoha pksoah pkshoa pkshao pksaho
pksaoh pkhsoa pkhsao pkhosa pkhoas pkhaos pkhaso pkasho pkasoh pkahso pkahos
pkaohs pkaosh pskoha pskoah pskhoa pskhao pskaho pskaoh psokha psokah psohka
psohak psoahk psoakh pshoka pshoak pshkoa pshkao pshako pshaok psaohk psaokh
psahok psahko psakho psakoh phksoa phksao phkosa phkoas phkaos phkaso phskoa
phskao phsoka phsoak phsaok phsako phoska phosak phoksa phokas phoaks phoask
phasok phasko phaosk phaoks phakos phakso paksho paksoh pakhso pakhos pakohs
pakosh paskho paskoh pashko pashok pasohk pasokh pahsko pahsok pahkso pahkos
pahoks pahosk paoshk paoskh paohsk paohks paokhs paoksh sopkha sopkah sophka
sophak sopahk sopakh sokpha sokpah sokhpa sokhap sokahp sokaph sohkpa sohkap
sohpka sohpak sohapk sohakp soakhp soakph soahkp soahpk soaphk soapkh spokha
spokah spohka spohak spoahk spoakh spkoha spkoah spkhoa spkhao spkaho spkaoh
sphkoa sphkao sphoka sphoak sphaok sphako spakho spakoh spahko spahok spaohk
spaokh skpoha skpoah skphoa skphao skpaho skpaoh skopha skopah skohpa skohap
skoahp skoaph skhopa skhoap skhpoa skhpao skhapo skhaop skaohp skaoph skahop
skahpo skapho skapoh shpkoa shpkao shpoka shpoak shpaok shpako shkpoa shkpao
shkopa shkoap shkaop shkapo shokpa shokap shopka shopak shoapk shoakp shakop
shakpo shaokp shaopk shapok shapko sapkho sapkoh saphko saphok sapohk sapokh
sakpho sakpoh sakhpo sakhop sakohp sakoph sahkpo sahkop sahpko sahpok sahopk
sahokp saokhp saokph saohkp saohpk saophk saopkh hopska hopsak hopksa hopkas
hopaks hopask hospka hospak hoskpa hoskap hosakp hosapk hokspa hoksap hokpsa
hokpas hokaps hokasp hoaskp hoaspk hoaksp hoakps hoapks hoapsk hposka hposak
hpoksa hpokas hpoaks hpoask hpsoka hpsoak hpskoa hpskao hpsako hpsaok hpksoa
hpksao hpkosa hpkoas hpkaos hpkaso hpasko hpasok hpakso hpakos hpaoks hpaosk
hspoka hspoak hspkoa hspkao hspako hspaok hsopka hsopak hsokpa hsokap hsoakp
hsoapk hskopa hskoap hskpoa hskpao hskapo hskaop hsaokp hsaopk hsakop hsakpo
hsapko hsapok hkpsoa hkpsao hkposa hkpoas hkpaos hkpaso hkspoa hkspao hksopa
hksoap hksaop hksapo hkospa hkosap hkopsa hkopas hkoaps hkoasp hkasop hkaspo
hkaosp hkaops hkapos hkapso hapsko hapsok hapkso hapkos hapoks haposk haspko
haspok haskpo haskop hasokp hasopk hakspo haksop hakpso hakpos hakops hakosp
haoskp haospk haoksp haokps haopks haopsk aopshk aopskh aophsk aophks aopkhs
aopksh aosphk aospkh aoshpk aoshkp aoskhp aoskph aohspk aohskp aohpsk aohpks
aohkps aohksp aokshp aoksph aokhsp aokhps aokphs aokpsh aposhk aposkh apohsk
apohks apokhs apoksh apsohk apsokh apshok apshko apskho apskoh aphsok aphsko
aphosk aphoks aphkos aphkso apksho apksoh apkhso apkhos apkohs apkosh aspohk
aspokh asphok asphko aspkho aspkoh asophk asopkh asohpk asohkp asokhp asokph
ashopk ashokp ashpok ashpko ashkpo ashkop askohp askoph askhop askhpo askpho
askpoh ahpsok ahpsko ahposk ahpoks ahpkos ahpkso ahspok ahspko ahsopk ahsokp
ahskop ahskpo ahospk ahoskp ahopsk ahopks ahokps ahoksp ahksop ahkspo ahkosp
ahkops ahkpos ahkpso akpsho akpsoh akphso akphos akpohs akposh akspho akspoh
akshpo akshop aksohp aksoph akhspo akhsop akhpso akhpos akhops akhosp akoshp
akosph akohsp akohps akophs akopsh

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History of cryptography
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