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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: dirosa
cipher variations:
ejsptb fktquc glurvd hmvswe inwtxf
joxuyg kpyvzh lqzwai mraxbj nsbyck
otczdl pudaem qvebfn rwfcgo sxgdhp
tyheiq uzifjr vajgks wbkhlt xclimu
ydmjnv zenkow afolpx bgpmqy chqnrz

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: dirosa
Cipher: wrilhz

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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: dirosa

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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: dirosa
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: dirosa
Cipher: qvebfn

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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: dirosa
Cipher: 414224433411

Extended Methods:
Method #1

Plaintext: dirosa
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
d i r o s a 
4 4 2 4 3 1 
1 2 4 3 4 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: dirosa
Cipher: trcfod

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Method #3

Plaintext: dirosa
method variations:
qgtndq gtndqq tndqqg
ndqqgt dqqgtn qqgtnd

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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: dirosa

all 720 cipher variations:
dirosa diroas dirsoa dirsao diraso diraos diorsa dioras diosra diosar dioasr
dioars disora disoar disroa disrao disaro disaor diaosr diaors diasor diasro
diarso diaros driosa drioas drisoa drisao driaso driaos droisa droias drosia
drosai droasi droais drsoia drsoai drsioa drsiao drsaio drsaoi draosi draois
drasoi drasio draiso draios dorisa dorias dorsia dorsai dorasi dorais doirsa
doiras doisra doisar doiasr doiars dosira dosiar dosria dosrai dosari dosair
doaisr doairs doasir doasri doarsi doaris dsroia dsroai dsrioa dsriao dsraio
dsraoi dsoria dsorai dsoira dsoiar dsoair dsoari dsiora dsioar dsiroa dsirao
dsiaro dsiaor dsaoir dsaori dsaior dsairo dsario dsaroi darosi darois darsoi
darsio dariso darios daorsi daoris daosri daosir daoisr daoirs dasori dasoir
dasroi dasrio dasiro dasior daiosr daiors daisor daisro dairso dairos idrosa
idroas idrsoa idrsao idraso idraos idorsa idoras idosra idosar idoasr idoars
idsora idsoar idsroa idsrao idsaro idsaor idaosr idaors idasor idasro idarso
idaros irdosa irdoas irdsoa irdsao irdaso irdaos irodsa irodas irosda irosad
iroasd iroads irsoda irsoad irsdoa irsdao irsado irsaod iraosd iraods irasod
irasdo iradso irados iordsa iordas iorsda iorsad iorasd iorads iodrsa iodras
iodsra iodsar iodasr iodars iosdra iosdar iosrda iosrad iosard iosadr ioadsr
ioadrs ioasdr ioasrd ioarsd ioards isroda isroad isrdoa isrdao isrado israod
isorda isorad isodra isodar isoadr isoard isdora isdoar isdroa isdrao isdaro
isdaor isaodr isaord isador isadro isardo isarod iarosd iarods iarsod iarsdo
iardso iardos iaorsd iaords iaosrd iaosdr iaodsr iaodrs iasord iasodr iasrod
iasrdo iasdro iasdor iadosr iadors iadsor iadsro iadrso iadros ridosa ridoas
ridsoa ridsao ridaso ridaos riodsa riodas riosda riosad rioasd rioads risoda
risoad risdoa risdao risado risaod riaosd riaods riasod riasdo riadso riados
rdiosa rdioas rdisoa rdisao rdiaso rdiaos rdoisa rdoias rdosia rdosai rdoasi
rdoais rdsoia rdsoai rdsioa rdsiao rdsaio rdsaoi rdaosi rdaois rdasoi rdasio
rdaiso rdaios rodisa rodias rodsia rodsai rodasi rodais roidsa roidas roisda
roisad roiasd roiads rosida rosiad rosdia rosdai rosadi rosaid roaisd roaids
roasid roasdi roadsi roadis rsdoia rsdoai rsdioa rsdiao rsdaio rsdaoi rsodia
rsodai rsoida rsoiad rsoaid rsoadi rsioda rsioad rsidoa rsidao rsiado rsiaod
rsaoid rsaodi rsaiod rsaido rsadio rsadoi radosi radois radsoi radsio radiso
radios raodsi raodis raosdi raosid raoisd raoids rasodi rasoid rasdoi rasdio
rasido rasiod raiosd raiods raisod raisdo raidso raidos oirdsa oirdas oirsda
oirsad oirasd oirads oidrsa oidras oidsra oidsar oidasr oidars oisdra oisdar
oisrda oisrad oisard oisadr oiadsr oiadrs oiasdr oiasrd oiarsd oiards oridsa
oridas orisda orisad oriasd oriads ordisa ordias ordsia ordsai ordasi ordais
orsdia orsdai orsida orsiad orsaid orsadi oradsi oradis orasdi orasid oraisd
oraids odrisa odrias odrsia odrsai odrasi odrais odirsa odiras odisra odisar
odiasr odiars odsira odsiar odsria odsrai odsari odsair odaisr odairs odasir
odasri odarsi odaris osrdia osrdai osrida osriad osraid osradi osdria osdrai
osdira osdiar osdair osdari osidra osidar osirda osirad osiard osiadr osadir
osadri osaidr osaird osarid osardi oardsi oardis oarsdi oarsid oarisd oarids
oadrsi oadris oadsri oadsir oadisr oadirs oasdri oasdir oasrdi oasrid oasird
oasidr oaidsr oaidrs oaisdr oaisrd oairsd oairds siroda siroad sirdoa sirdao
sirado siraod siorda siorad siodra siodar sioadr sioard sidora sidoar sidroa
sidrao sidaro sidaor siaodr siaord siador siadro siardo siarod srioda srioad
sridoa sridao sriado sriaod sroida sroiad srodia srodai sroadi sroaid srdoia
srdoai srdioa srdiao srdaio srdaoi sraodi sraoid sradoi sradio sraido sraiod
sorida soriad sordia sordai soradi soraid soirda soirad soidra soidar soiadr
soiard sodira sodiar sodria sodrai sodari sodair soaidr soaird soadir soadri
soardi soarid sdroia sdroai sdrioa sdriao sdraio sdraoi sdoria sdorai sdoira
sdoiar sdoair sdoari sdiora sdioar sdiroa sdirao sdiaro sdiaor sdaoir sdaori
sdaior sdairo sdario sdaroi sarodi saroid sardoi sardio sarido sariod saordi
saorid saodri saodir saoidr saoird sadori sadoir sadroi sadrio sadiro sadior
saiodr saiord saidor saidro sairdo sairod airosd airods airsod airsdo airdso
airdos aiorsd aiords aiosrd aiosdr aiodsr aiodrs aisord aisodr aisrod aisrdo
aisdro aisdor aidosr aidors aidsor aidsro aidrso aidros ariosd ariods arisod
arisdo aridso aridos aroisd aroids arosid arosdi arodsi arodis arsoid arsodi
arsiod arsido arsdio arsdoi ardosi ardois ardsoi ardsio ardiso ardios aorisd
aorids aorsid aorsdi aordsi aordis aoirsd aoirds aoisrd aoisdr aoidsr aoidrs
aosird aosidr aosrid aosrdi aosdri aosdir aodisr aodirs aodsir aodsri aodrsi
aodris asroid asrodi asriod asrido asrdio asrdoi asorid asordi asoird asoidr
asodir asodri asiord asiodr asirod asirdo asidro asidor asdoir asdori asdior
asdiro asdrio asdroi adrosi adrois adrsoi adrsio adriso adrios adorsi adoris
adosri adosir adoisr adoirs adsori adsoir adsroi adsrio adsiro adsior adiosr
adiors adisor adisro adirso adiros

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History of cryptography
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