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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: yendor
cipher variations:
zfoeps agpfqt bhqgru cirhsv djsitw
ektjux flukvy gmvlwz hnwmxa ioxnyb
jpyozc kqzpad lraqbe msbrcf ntcsdg
oudteh pveufi qwfvgj rxgwhk syhxil
tziyjm uajzkn vbkalo wclbmp xdmcnq

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: yendor
Cipher: bvmwli

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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: yendor

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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: yendor
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: yendor
Cipher: lraqbe

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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: yendor
Cipher: 455133414324

Extended Methods:
Method #1

Plaintext: yendor
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
y e n d o r 
4 5 3 4 4 2 
5 1 3 1 3 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: yendor
Cipher: ysiecs

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Method #3

Plaintext: yendor
method variations:
zlsqht lsqhtz sqhtzl
qhtzls htzlsq tzlsqh

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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: yendor

all 720 cipher variations:
yendor yendro yenodr yenord yenrod yenrdo yednor yednro yedonr yedorn yedron
yedrno yeodnr yeodrn yeondr yeonrd yeornd yeordn yerdon yerdno yerodn yerond
yernod yerndo ynedor ynedro yneodr yneord ynerod ynerdo yndeor yndero yndoer
yndore yndroe yndreo ynoder ynodre ynoedr ynoerd ynored ynorde ynrdoe ynrdeo
ynrode ynroed ynreod ynredo ydneor ydnero ydnoer ydnore ydnroe ydnreo ydenor
ydenro ydeonr ydeorn yderon yderno ydoenr ydoern ydoner ydonre ydorne ydoren
ydreon ydreno ydroen ydrone ydrnoe ydrneo yonder yondre yonedr yonerd yonred
yonrde yodner yodnre yodenr yodern yodren yodrne yoednr yoedrn yoendr yoenrd
yoernd yoerdn yorden yordne yoredn yorend yorned yornde yrndoe yrndeo yrnode
yrnoed yrneod yrnedo yrdnoe yrdneo yrdone yrdoen yrdeon yrdeno yrodne yroden
yronde yroned yroend yroedn yredon yredno yreodn yreond yrenod yrendo eyndor
eyndro eynodr eynord eynrod eynrdo eydnor eydnro eydonr eydorn eydron eydrno
eyodnr eyodrn eyondr eyonrd eyornd eyordn eyrdon eyrdno eyrodn eyrond eyrnod
eyrndo enydor enydro enyodr enyord enyrod enyrdo endyor endyro endoyr endory
endroy endryo enodyr enodry enoydr enoyrd enoryd enordy enrdoy enrdyo enrody
enroyd enryod enrydo ednyor ednyro ednoyr ednory ednroy ednryo edynor edynro
edyonr edyorn edyron edyrno edoynr edoyrn edonyr edonry edorny edoryn edryon
edryno edroyn edrony edrnoy edrnyo eondyr eondry eonydr eonyrd eonryd eonrdy
eodnyr eodnry eodynr eodyrn eodryn eodrny eoydnr eoydrn eoyndr eoynrd eoyrnd
eoyrdn eordyn eordny eorydn eorynd eornyd eorndy erndoy erndyo ernody ernoyd
ernyod ernydo erdnoy erdnyo erdony erdoyn erdyon erdyno erodny erodyn erondy
eronyd eroynd eroydn erydon erydno eryodn eryond erynod eryndo neydor neydro
neyodr neyord neyrod neyrdo nedyor nedyro nedoyr nedory nedroy nedryo neodyr
neodry neoydr neoyrd neoryd neordy nerdoy nerdyo nerody neroyd neryod nerydo
nyedor nyedro nyeodr nyeord nyerod nyerdo nydeor nydero nydoer nydore nydroe
nydreo nyoder nyodre nyoedr nyoerd nyored nyorde nyrdoe nyrdeo nyrode nyroed
nyreod nyredo ndyeor ndyero ndyoer ndyore ndyroe ndyreo ndeyor ndeyro ndeoyr
ndeory nderoy nderyo ndoeyr ndoery ndoyer ndoyre ndorye ndorey ndreoy ndreyo
ndroey ndroye ndryoe ndryeo noyder noydre noyedr noyerd noyred noyrde nodyer
nodyre nodeyr nodery nodrey nodrye noedyr noedry noeydr noeyrd noeryd noerdy
nordey nordye noredy noreyd noryed noryde nrydoe nrydeo nryode nryoed nryeod
nryedo nrdyoe nrdyeo nrdoye nrdoey nrdeoy nrdeyo nrodye nrodey nroyde nroyed
nroeyd nroedy nredoy nredyo nreody nreoyd nreyod nreydo denyor denyro denoyr
denory denroy denryo deynor deynro deyonr deyorn deyron deyrno deoynr deoyrn
deonyr deonry deorny deoryn deryon deryno deroyn derony dernoy dernyo dneyor
dneyro dneoyr dneory dneroy dneryo dnyeor dnyero dnyoer dnyore dnyroe dnyreo
dnoyer dnoyre dnoeyr dnoery dnorey dnorye dnryoe dnryeo dnroye dnroey dnreoy
dnreyo dyneor dynero dynoer dynore dynroe dynreo dyenor dyenro dyeonr dyeorn
dyeron dyerno dyoenr dyoern dyoner dyonre dyorne dyoren dyreon dyreno dyroen
dyrone dyrnoe dyrneo donyer donyre doneyr donery donrey donrye doyner doynre
doyenr doyern doyren doyrne doeynr doeyrn doenyr doenry doerny doeryn doryen
doryne doreyn doreny dorney dornye drnyoe drnyeo drnoye drnoey drneoy drneyo
drynoe dryneo dryone dryoen dryeon dryeno droyne droyen dronye droney droeny
droeyn dreyon dreyno dreoyn dreony drenoy drenyo oendyr oendry oenydr oenyrd
oenryd oenrdy oednyr oednry oedynr oedyrn oedryn oedrny oeydnr oeydrn oeyndr
oeynrd oeyrnd oeyrdn oerdyn oerdny oerydn oerynd oernyd oerndy onedyr onedry
oneydr oneyrd oneryd onerdy ondeyr ondery ondyer ondyre ondrye ondrey onyder
onydre onyedr onyerd onyred onyrde onrdye onrdey onryde onryed onreyd onredy
odneyr odnery odnyer odnyre odnrye odnrey odenyr odenry odeynr odeyrn oderyn
oderny odyenr odyern odyner odynre odyrne odyren odreyn odreny odryen odryne
odrnye odrney oynder oyndre oynedr oynerd oynred oynrde oydner oydnre oydenr
oydern oydren oydrne oyednr oyedrn oyendr oyenrd oyernd oyerdn oyrden oyrdne
oyredn oyrend oyrned oyrnde orndye orndey ornyde ornyed orneyd ornedy ordnye
ordney ordyne ordyen ordeyn ordeny orydne oryden orynde oryned oryend oryedn
oredyn oredny oreydn oreynd orenyd orendy rendoy rendyo renody renoyd renyod
renydo rednoy rednyo redony redoyn redyon redyno reodny reodyn reondy reonyd
reoynd reoydn reydon reydno reyodn reyond reynod reyndo rnedoy rnedyo rneody
rneoyd rneyod rneydo rndeoy rndeyo rndoey rndoye rndyoe rndyeo rnodey rnodye
rnoedy rnoeyd rnoyed rnoyde rnydoe rnydeo rnyode rnyoed rnyeod rnyedo rdneoy
rdneyo rdnoey rdnoye rdnyoe rdnyeo rdenoy rdenyo rdeony rdeoyn rdeyon rdeyno
rdoeny rdoeyn rdoney rdonye rdoyne rdoyen rdyeon rdyeno rdyoen rdyone rdynoe
rdyneo rondey rondye ronedy roneyd ronyed ronyde rodney rodnye rodeny rodeyn
rodyen rodyne roedny roedyn roendy roenyd roeynd roeydn royden roydne royedn
royend royned roynde ryndoe ryndeo rynode rynoed ryneod rynedo rydnoe rydneo
rydone rydoen rydeon rydeno ryodne ryoden ryonde ryoned ryoend ryoedn ryedon
ryedno ryeodn ryeond ryenod ryendo

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History of cryptography
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