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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: rustad
cipher variations:
svtube twuvcf uxvwdg vywxeh wzxyfi
xayzgj ybzahk zcabil adbcjm becdkn
cfdelo dgefmp ehfgnq fighor gjhips
hkijqt iljkru jmklsv knlmtw lomnux
mpnovy nqopwz orpqxa psqryb qtrszc

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: rustad
Cipher: ifhgzw

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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: rustad

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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: rustad
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: rustad
Cipher: ehfgnq

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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: rustad
Cipher: 245434441141

Extended Methods:
Method #1

Plaintext: rustad
method variations:

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

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Method #3

Plaintext: rustad
method variations:
yotdqf otdqfy tdqfyo
dqfyot qfyotd fyotdq

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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: rustad

all 720 cipher variations:
rustad rustda rusatd rusadt rusdat rusdta rutsad rutsda rutasd rutads rutdas
rutdsa ruatsd ruatds ruastd ruasdt ruadst ruadts rudtas rudtsa rudats rudast
rudsat rudsta rsutad rsutda rsuatd rsuadt rsudat rsudta rstuad rstuda rstaud
rstadu rstdau rstdua rsatud rsatdu rsautd rsaudt rsadut rsadtu rsdtau rsdtua
rsdatu rsdaut rsduat rsduta rtsuad rtsuda rtsaud rtsadu rtsdau rtsdua rtusad
rtusda rtuasd rtuads rtudas rtudsa rtausd rtauds rtasud rtasdu rtadsu rtadus
rtduas rtdusa rtdaus rtdasu rtdsau rtdsua rastud rastdu rasutd rasudt rasdut
rasdtu ratsud ratsdu ratusd ratuds ratdus ratdsu rautsd rautds raustd rausdt
raudst raudts radtus radtsu raduts radust radsut radstu rdstau rdstua rdsatu
rdsaut rdsuat rdsuta rdtsau rdtsua rdtasu rdtaus rdtuas rdtusa rdatsu rdatus
rdastu rdasut rdaust rdauts rdutas rdutsa rduats rduast rdusat rdusta urstad
urstda ursatd ursadt ursdat ursdta urtsad urtsda urtasd urtads urtdas urtdsa
uratsd uratds urastd urasdt uradst uradts urdtas urdtsa urdats urdast urdsat
urdsta usrtad usrtda usratd usradt usrdat usrdta ustrad ustrda ustard ustadr
ustdar ustdra usatrd usatdr usartd usardt usadrt usadtr usdtar usdtra usdatr
usdart usdrat usdrta utsrad utsrda utsard utsadr utsdar utsdra utrsad utrsda
utrasd utrads utrdas utrdsa utarsd utards utasrd utasdr utadsr utadrs utdras
utdrsa utdars utdasr utdsar utdsra uastrd uastdr uasrtd uasrdt uasdrt uasdtr
uatsrd uatsdr uatrsd uatrds uatdrs uatdsr uartsd uartds uarstd uarsdt uardst
uardts uadtrs uadtsr uadrts uadrst uadsrt uadstr udstar udstra udsatr udsart
udsrat udsrta udtsar udtsra udtasr udtars udtras udtrsa udatsr udatrs udastr
udasrt udarst udarts udrtas udrtsa udrats udrast udrsat udrsta surtad surtda
suratd suradt surdat surdta sutrad sutrda sutard sutadr sutdar sutdra suatrd
suatdr suartd suardt suadrt suadtr sudtar sudtra sudatr sudart sudrat sudrta
srutad srutda sruatd sruadt srudat srudta srtuad srtuda srtaud srtadu srtdau
srtdua sratud sratdu srautd sraudt sradut sradtu srdtau srdtua srdatu srdaut
srduat srduta struad struda straud stradu strdau strdua sturad sturda stuard
stuadr studar studra staurd staudr starud stardu stadru stadur stduar stdura
stdaur stdaru stdrau stdrua sartud sartdu sarutd sarudt sardut sardtu satrud
satrdu saturd satudr satdur satdru sautrd sautdr saurtd saurdt saudrt saudtr
sadtur sadtru sadutr sadurt sadrut sadrtu sdrtau sdrtua sdratu sdraut sdruat
sdruta sdtrau sdtrua sdtaru sdtaur sdtuar sdtura sdatru sdatur sdartu sdarut
sdaurt sdautr sdutar sdutra sduatr sduart sdurat sdurta tusrad tusrda tusard
tusadr tusdar tusdra tursad tursda turasd turads turdas turdsa tuarsd tuards
tuasrd tuasdr tuadsr tuadrs tudras tudrsa tudars tudasr tudsar tudsra tsurad
tsurda tsuard tsuadr tsudar tsudra tsruad tsruda tsraud tsradu tsrdau tsrdua
tsarud tsardu tsaurd tsaudr tsadur tsadru tsdrau tsdrua tsdaru tsdaur tsduar
tsdura trsuad trsuda trsaud trsadu trsdau trsdua trusad trusda truasd truads
trudas trudsa trausd trauds trasud trasdu tradsu tradus trduas trdusa trdaus
trdasu trdsau trdsua tasrud tasrdu tasurd tasudr tasdur tasdru tarsud tarsdu
tarusd taruds tardus tardsu taursd taurds tausrd tausdr taudsr taudrs tadrus
tadrsu tadurs tadusr tadsur tadsru tdsrau tdsrua tdsaru tdsaur tdsuar tdsura
tdrsau tdrsua tdrasu tdraus tdruas tdrusa tdarsu tdarus tdasru tdasur tdausr
tdaurs tduras tdursa tduars tduasr tdusar tdusra austrd austdr ausrtd ausrdt
ausdrt ausdtr autsrd autsdr autrsd autrds autdrs autdsr aurtsd aurtds aurstd
aursdt aurdst aurdts audtrs audtsr audrts audrst audsrt audstr asutrd asutdr
asurtd asurdt asudrt asudtr asturd astudr astrud astrdu astdru astdur asrtud
asrtdu asrutd asrudt asrdut asrdtu asdtru asdtur asdrtu asdrut asdurt asdutr
atsurd atsudr atsrud atsrdu atsdru atsdur atusrd atusdr atursd aturds atudrs
atudsr atrusd atruds atrsud atrsdu atrdsu atrdus atdurs atdusr atdrus atdrsu
atdsru atdsur arstud arstdu arsutd arsudt arsdut arsdtu artsud artsdu artusd
artuds artdus artdsu arutsd arutds arustd arusdt arudst arudts ardtus ardtsu
arduts ardust ardsut ardstu adstru adstur adsrtu adsrut adsurt adsutr adtsru
adtsur adtrsu adtrus adturs adtusr adrtsu adrtus adrstu adrsut adrust adruts
adutrs adutsr adurts adurst adusrt adustr dustar dustra dusatr dusart dusrat
dusrta dutsar dutsra dutasr dutars dutras dutrsa duatsr duatrs duastr duasrt
duarst duarts durtas durtsa durats durast dursat dursta dsutar dsutra dsuatr
dsuart dsurat dsurta dstuar dstura dstaur dstaru dstrau dstrua dsatur dsatru
dsautr dsaurt dsarut dsartu dsrtau dsrtua dsratu dsraut dsruat dsruta dtsuar
dtsura dtsaur dtsaru dtsrau dtsrua dtusar dtusra dtuasr dtuars dturas dtursa
dtausr dtaurs dtasur dtasru dtarsu dtarus dtruas dtrusa dtraus dtrasu dtrsau
dtrsua dastur dastru dasutr dasurt dasrut dasrtu datsur datsru datusr daturs
datrus datrsu dautsr dautrs daustr dausrt daurst daurts dartus dartsu daruts
darust darsut darstu drstau drstua drsatu drsaut drsuat drsuta drtsau drtsua
drtasu drtaus drtuas drtusa dratsu dratus drastu drasut draust drauts drutas
drutsa druats druast drusat drusta

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History of cryptography
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