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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: netmac
cipher variations:
ofunbd pgvoce qhwpdf rixqeg sjyrfh
tkzsgi ulathj vmbuik wncvjl xodwkm
ypexln zqfymo argznp bshaoq ctibpr
dujcqs evkdrt fwlesu gxmftv hynguw
izohvx japiwy kbqjxz lcrkya mdslzb

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: netmac
Cipher: mvgnzx

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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: netmac

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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: netmac
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: netmac
Cipher: argznp

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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: netmac
Cipher: 335144231131

Extended Methods:
Method #1

Plaintext: netmac
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
n e t m a c 
3 5 4 2 1 3 
3 1 4 3 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: netmac
Cipher: xilcoa

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Method #3

Plaintext: netmac
method variations:
xqicll qicllx icllxq
cllxqi llxqic lxqicl

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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: netmac

all 720 cipher variations:
netmac netmca netamc netacm netcam netcma nemtac nemtca nematc nemact nemcat
nemcta neamtc neamct neatmc neatcm neactm neacmt necmat necmta necamt necatm
nectam nectma ntemac ntemca nteamc nteacm ntecam ntecma ntmeac ntmeca ntmaec
ntmace ntmcae ntmcea ntamec ntamce ntaemc ntaecm ntacem ntacme ntcmae ntcmea
ntcame ntcaem ntceam ntcema nmteac nmteca nmtaec nmtace nmtcae nmtcea nmetac
nmetca nmeatc nmeact nmecat nmecta nmaetc nmaect nmatec nmatce nmacte nmacet
nmceat nmceta nmcaet nmcate nmctae nmctea natmec natmce natemc natecm natcem
natcme namtec namtce nametc namect namcet namcte naemtc naemct naetmc naetcm
naectm naecmt nacmet nacmte nacemt nacetm nactem nactme nctmae nctmea nctame
nctaem ncteam nctema ncmtae ncmtea ncmate ncmaet ncmeat ncmeta ncamte ncamet
ncatme ncatem ncaetm ncaemt ncemat ncemta nceamt nceatm ncetam ncetma entmac
entmca entamc entacm entcam entcma enmtac enmtca enmatc enmact enmcat enmcta
enamtc enamct enatmc enatcm enactm enacmt encmat encmta encamt encatm enctam
enctma etnmac etnmca etnamc etnacm etncam etncma etmnac etmnca etmanc etmacn
etmcan etmcna etamnc etamcn etanmc etancm etacnm etacmn etcman etcmna etcamn
etcanm etcnam etcnma emtnac emtnca emtanc emtacn emtcan emtcna emntac emntca
emnatc emnact emncat emncta emantc emanct ematnc ematcn emactn emacnt emcnat
emcnta emcant emcatn emctan emctna eatmnc eatmcn eatnmc eatncm eatcnm eatcmn
eamtnc eamtcn eamntc eamnct eamcnt eamctn eanmtc eanmct eantmc eantcm eanctm
eancmt eacmnt eacmtn eacnmt eacntm eactnm eactmn ectman ectmna ectamn ectanm
ectnam ectnma ecmtan ecmtna ecmatn ecmant ecmnat ecmnta ecamtn ecamnt ecatmn
ecatnm ecantm ecanmt ecnmat ecnmta ecnamt ecnatm ecntam ecntma tenmac tenmca
tenamc tenacm tencam tencma temnac temnca temanc temacn temcan temcna teamnc
teamcn teanmc teancm teacnm teacmn tecman tecmna tecamn tecanm tecnam tecnma
tnemac tnemca tneamc tneacm tnecam tnecma tnmeac tnmeca tnmaec tnmace tnmcae
tnmcea tnamec tnamce tnaemc tnaecm tnacem tnacme tncmae tncmea tncame tncaem
tnceam tncema tmneac tmneca tmnaec tmnace tmncae tmncea tmenac tmenca tmeanc
tmeacn tmecan tmecna tmaenc tmaecn tmanec tmance tmacne tmacen tmcean tmcena
tmcaen tmcane tmcnae tmcnea tanmec tanmce tanemc tanecm tancem tancme tamnec
tamnce tamenc tamecn tamcen tamcne taemnc taemcn taenmc taencm taecnm taecmn
tacmen tacmne tacemn tacenm tacnem tacnme tcnmae tcnmea tcname tcnaem tcneam
tcnema tcmnae tcmnea tcmane tcmaen tcmean tcmena tcamne tcamen tcanme tcanem
tcaenm tcaemn tceman tcemna tceamn tceanm tcenam tcenma metnac metnca metanc
metacn metcan metcna mentac mentca menatc menact mencat mencta meantc meanct
meatnc meatcn meactn meacnt mecnat mecnta mecant mecatn mectan mectna mtenac
mtenca mteanc mteacn mtecan mtecna mtneac mtneca mtnaec mtnace mtncae mtncea
mtanec mtance mtaenc mtaecn mtacen mtacne mtcnae mtcnea mtcane mtcaen mtcean
mtcena mnteac mnteca mntaec mntace mntcae mntcea mnetac mnetca mneatc mneact
mnecat mnecta mnaetc mnaect mnatec mnatce mnacte mnacet mnceat mnceta mncaet
mncate mnctae mnctea matnec matnce matenc matecn matcen matcne mantec mantce
manetc manect mancet mancte maentc maenct maetnc maetcn maectn maecnt macnet
macnte macent macetn macten mactne mctnae mctnea mctane mctaen mctean mctena
mcntae mcntea mcnate mcnaet mcneat mcneta mcante mcanet mcatne mcaten mcaetn
mcaent mcenat mcenta mceant mceatn mcetan mcetna aetmnc aetmcn aetnmc aetncm
aetcnm aetcmn aemtnc aemtcn aemntc aemnct aemcnt aemctn aenmtc aenmct aentmc
aentcm aenctm aencmt aecmnt aecmtn aecnmt aecntm aectnm aectmn atemnc atemcn
atenmc atencm atecnm atecmn atmenc atmecn atmnec atmnce atmcne atmcen atnmec
atnmce atnemc atnecm atncem atncme atcmne atcmen atcnme atcnem atcenm atcemn
amtenc amtecn amtnec amtnce amtcne amtcen ametnc ametcn amentc amenct amecnt
amectn amnetc amnect amntec amntce amncte amncet amcent amcetn amcnet amcnte
amctne amcten antmec antmce antemc antecm antcem antcme anmtec anmtce anmetc
anmect anmcet anmcte anemtc anemct anetmc anetcm anectm anecmt ancmet ancmte
ancemt ancetm anctem anctme actmne actmen actnme actnem actenm actemn acmtne
acmten acmnte acmnet acment acmetn acnmte acnmet acntme acntem acnetm acnemt
acemnt acemtn acenmt acentm acetnm acetmn cetman cetmna cetamn cetanm cetnam
cetnma cemtan cemtna cematn cemant cemnat cemnta ceamtn ceamnt ceatmn ceatnm
ceantm ceanmt cenmat cenmta cenamt cenatm centam centma cteman ctemna cteamn
cteanm ctenam ctenma ctmean ctmena ctmaen ctmane ctmnae ctmnea ctamen ctamne
ctaemn ctaenm ctanem ctanme ctnmae ctnmea ctname ctnaem ctneam ctnema cmtean
cmtena cmtaen cmtane cmtnae cmtnea cmetan cmetna cmeatn cmeant cmenat cmenta
cmaetn cmaent cmaten cmatne cmante cmanet cmneat cmneta cmnaet cmnate cmntae
cmntea catmen catmne catemn catenm catnem catnme camten camtne cametn cament
camnet camnte caemtn caemnt caetmn caetnm caentm caenmt canmet canmte canemt
canetm cantem cantme cntmae cntmea cntame cntaem cnteam cntema cnmtae cnmtea
cnmate cnmaet cnmeat cnmeta cnamte cnamet cnatme cnatem cnaetm cnaemt cnemat
cnemta cneamt cneatm cnetam cnetma

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History of cryptography
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