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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: oudart
cipher variations:
pvebsu qwfctv rxgduw syhevx tzifwy
uajgxz vbkhya wclizb xdmjac yenkbd
zfolce agpmdf bhqneg cirofh djspgi
ektqhj flurik gmvsjl hnwtkm ioxuln
jpyvmo kqzwnp lraxoq msbypr ntczqs

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: oudart
Cipher: lfwzig

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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: oudart

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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: oudart
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: oudart
Cipher: bhqneg

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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: oudart
Cipher: 435441112444

Extended Methods:
Method #1

Plaintext: oudart
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
o u d a r t 
4 5 4 1 2 4 
3 4 1 1 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: oudart
Cipher: ydrsat

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Method #3

Plaintext: oudart
method variations:
xtaftt tafttx afttxt
fttxta ttxtaf txtaft

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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: oudart

all 720 cipher variations:
oudart oudatr oudrat oudrta oudtra oudtar ouadrt ouadtr ouardt ouartd ouatrd
ouatdr ouradt ouratd ourdat ourdta ourtda ourtad outard outadr outrad outrda
outdra outdar oduart oduatr odurat odurta odutra odutar odaurt odautr odarut
odartu odatru odatur odraut odratu odruat odruta odrtua odrtau odtaru odtaur
odtrau odtrua odtura odtuar oadurt oadutr oadrut oadrtu oadtru oadtur oaudrt
oaudtr oaurdt oaurtd oautrd oautdr oarudt oarutd oardut oardtu oartdu oartud
oaturd oatudr oatrud oatrdu oatdru oatdur ordaut ordatu orduat orduta ordtua
ordtau oradut oradtu oraudt orautd oratud oratdu oruadt oruatd orudat orudta
orutda orutad ortaud ortadu ortuad ortuda ortdua ortdau otdaru otdaur otdrau
otdrua otdura otduar otadru otadur otardu otarud otaurd otaudr otradu otraud
otrdau otrdua otruda otruad otuard otuadr oturad oturda otudra otudar uodart
uodatr uodrat uodrta uodtra uodtar uoadrt uoadtr uoardt uoartd uoatrd uoatdr
uoradt uoratd uordat uordta uortda uortad uotard uotadr uotrad uotrda uotdra
uotdar udoart udoatr udorat udorta udotra udotar udaort udaotr udarot udarto
udatro udator udraot udrato udroat udrota udrtoa udrtao udtaro udtaor udtrao
udtroa udtora udtoar uadort uadotr uadrot uadrto uadtro uadtor uaodrt uaodtr
uaordt uaortd uaotrd uaotdr uarodt uarotd uardot uardto uartdo uartod uatord
uatodr uatrod uatrdo uatdro uatdor urdaot urdato urdoat urdota urdtoa urdtao
uradot uradto uraodt uraotd uratod uratdo uroadt uroatd urodat urodta urotda
urotad urtaod urtado urtoad urtoda urtdoa urtdao utdaro utdaor utdrao utdroa
utdora utdoar utadro utador utardo utarod utaord utaodr utrado utraod utrdao
utrdoa utroda utroad utoard utoadr utorad utorda utodra utodar duoart duoatr
duorat duorta duotra duotar duaort duaotr duarot duarto duatro duator duraot
durato duroat durota durtoa durtao dutaro dutaor dutrao dutroa dutora dutoar
douart douatr dourat dourta doutra doutar doaurt doautr doarut doartu doatru
doatur doraut doratu doruat doruta dortua dortau dotaru dotaur dotrau dotrua
dotura dotuar daourt daoutr daorut daortu daotru daotur dauort dauotr daurot
daurto dautro dautor daruot daruto darout darotu dartou dartuo daturo datuor
datruo datrou datoru datour droaut droatu drouat drouta drotua drotau draout
draotu drauot drauto dratuo dratou druaot druato druoat druota drutoa drutao
drtauo drtaou drtuao drtuoa drtoua drtoau dtoaru dtoaur dtorau dtorua dtoura
dtouar dtaoru dtaour dtarou dtaruo dtauro dtauor dtraou dtrauo dtroau dtroua
dtruoa dtruao dtuaro dtuaor dturao dturoa dtuora dtuoar audort audotr audrot
audrto audtro audtor auodrt auodtr auordt auortd auotrd auotdr aurodt aurotd
aurdot aurdto aurtdo aurtod autord autodr autrod autrdo autdro autdor aduort
aduotr adurot adurto adutro adutor adourt adoutr adorut adortu adotru adotur
adrout adrotu adruot adruto adrtuo adrtou adtoru adtour adtrou adtruo adturo
adtuor aodurt aodutr aodrut aodrtu aodtru aodtur aoudrt aoudtr aourdt aourtd
aoutrd aoutdr aorudt aorutd aordut aordtu aortdu aortud aoturd aotudr aotrud
aotrdu aotdru aotdur ardout ardotu arduot arduto ardtuo ardtou arodut arodtu
aroudt aroutd arotud arotdu aruodt aruotd arudot arudto arutdo arutod artoud
artodu artuod artudo artduo artdou atdoru atdour atdrou atdruo atduro atduor
atodru atodur atordu atorud atourd atoudr atrodu atroud atrdou atrduo atrudo
atruod atuord atuodr aturod aturdo atudro atudor rudaot rudato rudoat rudota
rudtoa rudtao ruadot ruadto ruaodt ruaotd ruatod ruatdo ruoadt ruoatd ruodat
ruodta ruotda ruotad rutaod rutado rutoad rutoda rutdoa rutdao rduaot rduato
rduoat rduota rdutoa rdutao rdauot rdauto rdaout rdaotu rdatou rdatuo rdoaut
rdoatu rdouat rdouta rdotua rdotau rdtaou rdtauo rdtoau rdtoua rdtuoa rdtuao
raduot raduto radout radotu radtou radtuo raudot raudto rauodt rauotd rautod
rautdo raoudt raoutd raodut raodtu raotdu raotud ratuod ratudo ratoud ratodu
ratdou ratduo rodaut rodatu roduat roduta rodtua rodtau roadut roadtu roaudt
roautd roatud roatdu rouadt rouatd roudat roudta routda routad rotaud rotadu
rotuad rotuda rotdua rotdau rtdaou rtdauo rtdoau rtdoua rtduoa rtduao rtadou
rtaduo rtaodu rtaoud rtauod rtaudo rtoadu rtoaud rtodau rtodua rtouda rtouad
rtuaod rtuado rtuoad rtuoda rtudoa rtudao tudaro tudaor tudrao tudroa tudora
tudoar tuadro tuador tuardo tuarod tuaord tuaodr turado turaod turdao turdoa
turoda turoad tuoard tuoadr tuorad tuorda tuodra tuodar tduaro tduaor tdurao
tduroa tduora tduoar tdauro tdauor tdaruo tdarou tdaoru tdaour tdrauo tdraou
tdruao tdruoa tdroua tdroau tdoaru tdoaur tdorau tdorua tdoura tdouar taduro
taduor tadruo tadrou tadoru tadour taudro taudor taurdo taurod tauord tauodr
tarudo taruod tarduo tardou tarodu taroud taourd taoudr taorud taordu taodru
taodur trdauo trdaou trduao trduoa trdoua trdoau traduo tradou traudo trauod
traoud traodu truado truaod trudao trudoa truoda truoad troaud troadu trouad
trouda trodua trodau todaru todaur todrau todrua todura toduar toadru toadur
toardu toarud toaurd toaudr toradu toraud tordau tordua toruda toruad touard
touadr tourad tourda toudra toudar

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History of cryptography
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