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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: cymoid
cipher variations:
dznpje eaoqkf fbprlg gcqsmh hdrtni
iesuoj jftvpk kguwql lhvxrm miwysn
njxzto okyaup plzbvq qmacwr rnbdxs
soceyt tpdfzu uqegav vrfhbw wsgicx
xthjdy yuikez zvjlfa awkmgb bxlnhc

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: cymoid
Cipher: xbnlrw

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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: cymoid

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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: cymoid
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: cymoid
Cipher: plzbvq

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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: cymoid
Cipher: 314523434241

Extended Methods:
Method #1

Plaintext: cymoid
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
c y m o i d 
3 4 2 4 4 4 
1 5 3 3 2 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: cymoid
Cipher: srtvnb

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Method #3

Plaintext: cymoid
method variations:
qkssrl kssrlq ssrlqk
srlqks rlqkss lqkssr

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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: cymoid

all 720 cipher variations:
cymoid cymodi cymiod cymido cymdio cymdoi cyomid cyomdi cyoimd cyoidm cyodim
cyodmi cyiomd cyiodm cyimod cyimdo cyidmo cyidom cydoim cydomi cydiom cydimo
cydmio cydmoi cmyoid cmyodi cmyiod cmyido cmydio cmydoi cmoyid cmoydi cmoiyd
cmoidy cmodiy cmodyi cmioyd cmiody cmiyod cmiydo cmidyo cmidoy cmdoiy cmdoyi
cmdioy cmdiyo cmdyio cmdyoi comyid comydi comiyd comidy comdiy comdyi coymid
coymdi coyimd coyidm coydim coydmi coiymd coiydm coimyd coimdy coidmy coidym
codyim codymi codiym codimy codmiy codmyi cimoyd cimody cimyod cimydo cimdyo
cimdoy ciomyd ciomdy cioymd cioydm ciodym ciodmy ciyomd ciyodm ciymod ciymdo
ciydmo ciydom cidoym cidomy cidyom cidymo cidmyo cidmoy cdmoiy cdmoyi cdmioy
cdmiyo cdmyio cdmyoi cdomiy cdomyi cdoimy cdoiym cdoyim cdoymi cdiomy cdioym
cdimoy cdimyo cdiymo cdiyom cdyoim cdyomi cdyiom cdyimo cdymio cdymoi ycmoid
ycmodi ycmiod ycmido ycmdio ycmdoi ycomid ycomdi ycoimd ycoidm ycodim ycodmi
yciomd yciodm ycimod ycimdo ycidmo ycidom ycdoim ycdomi ycdiom ycdimo ycdmio
ycdmoi ymcoid ymcodi ymciod ymcido ymcdio ymcdoi ymocid ymocdi ymoicd ymoidc
ymodic ymodci ymiocd ymiodc ymicod ymicdo ymidco ymidoc ymdoic ymdoci ymdioc
ymdico ymdcio ymdcoi yomcid yomcdi yomicd yomidc yomdic yomdci yocmid yocmdi
yocimd yocidm yocdim yocdmi yoicmd yoicdm yoimcd yoimdc yoidmc yoidcm yodcim
yodcmi yodicm yodimc yodmic yodmci yimocd yimodc yimcod yimcdo yimdco yimdoc
yiomcd yiomdc yiocmd yiocdm yiodcm yiodmc yicomd yicodm yicmod yicmdo yicdmo
yicdom yidocm yidomc yidcom yidcmo yidmco yidmoc ydmoic ydmoci ydmioc ydmico
ydmcio ydmcoi ydomic ydomci ydoimc ydoicm ydocim ydocmi ydiomc ydiocm ydimoc
ydimco ydicmo ydicom ydcoim ydcomi ydciom ydcimo ydcmio ydcmoi mycoid mycodi
myciod mycido mycdio mycdoi myocid myocdi myoicd myoidc myodic myodci myiocd
myiodc myicod myicdo myidco myidoc mydoic mydoci mydioc mydico mydcio mydcoi
mcyoid mcyodi mcyiod mcyido mcydio mcydoi mcoyid mcoydi mcoiyd mcoidy mcodiy
mcodyi mcioyd mciody mciyod mciydo mcidyo mcidoy mcdoiy mcdoyi mcdioy mcdiyo
mcdyio mcdyoi mocyid mocydi mociyd mocidy mocdiy mocdyi moycid moycdi moyicd
moyidc moydic moydci moiycd moiydc moicyd moicdy moidcy moidyc modyic modyci
modiyc modicy modciy modcyi micoyd micody micyod micydo micdyo micdoy miocyd
miocdy mioycd mioydc miodyc miodcy miyocd miyodc miycod miycdo miydco miydoc
midoyc midocy midyoc midyco midcyo midcoy mdcoiy mdcoyi mdcioy mdciyo mdcyio
mdcyoi mdociy mdocyi mdoicy mdoiyc mdoyic mdoyci mdiocy mdioyc mdicoy mdicyo
mdiyco mdiyoc mdyoic mdyoci mdyioc mdyico mdycio mdycoi oymcid oymcdi oymicd
oymidc oymdic oymdci oycmid oycmdi oycimd oycidm oycdim oycdmi oyicmd oyicdm
oyimcd oyimdc oyidmc oyidcm oydcim oydcmi oydicm oydimc oydmic oydmci omycid
omycdi omyicd omyidc omydic omydci omcyid omcydi omciyd omcidy omcdiy omcdyi
omicyd omicdy omiycd omiydc omidyc omidcy omdciy omdcyi omdicy omdiyc omdyic
omdyci ocmyid ocmydi ocmiyd ocmidy ocmdiy ocmdyi ocymid ocymdi ocyimd ocyidm
ocydim ocydmi ociymd ociydm ocimyd ocimdy ocidmy ocidym ocdyim ocdymi ocdiym
ocdimy ocdmiy ocdmyi oimcyd oimcdy oimycd oimydc oimdyc oimdcy oicmyd oicmdy
oicymd oicydm oicdym oicdmy oiycmd oiycdm oiymcd oiymdc oiydmc oiydcm oidcym
oidcmy oidycm oidymc oidmyc oidmcy odmciy odmcyi odmicy odmiyc odmyic odmyci
odcmiy odcmyi odcimy odciym odcyim odcymi odicmy odicym odimcy odimyc odiymc
odiycm odycim odycmi odyicm odyimc odymic odymci iymocd iymodc iymcod iymcdo
iymdco iymdoc iyomcd iyomdc iyocmd iyocdm iyodcm iyodmc iycomd iycodm iycmod
iycmdo iycdmo iycdom iydocm iydomc iydcom iydcmo iydmco iydmoc imyocd imyodc
imycod imycdo imydco imydoc imoycd imoydc imocyd imocdy imodcy imodyc imcoyd
imcody imcyod imcydo imcdyo imcdoy imdocy imdoyc imdcoy imdcyo imdyco imdyoc
iomycd iomydc iomcyd iomcdy iomdcy iomdyc ioymcd ioymdc ioycmd ioycdm ioydcm
ioydmc iocymd iocydm iocmyd iocmdy iocdmy iocdym iodycm iodymc iodcym iodcmy
iodmcy iodmyc icmoyd icmody icmyod icmydo icmdyo icmdoy icomyd icomdy icoymd
icoydm icodym icodmy icyomd icyodm icymod icymdo icydmo icydom icdoym icdomy
icdyom icdymo icdmyo icdmoy idmocy idmoyc idmcoy idmcyo idmyco idmyoc idomcy
idomyc idocmy idocym idoycm idoymc idcomy idcoym idcmoy idcmyo idcymo idcyom
idyocm idyomc idycom idycmo idymco idymoc dymoic dymoci dymioc dymico dymcio
dymcoi dyomic dyomci dyoimc dyoicm dyocim dyocmi dyiomc dyiocm dyimoc dyimco
dyicmo dyicom dycoim dycomi dyciom dycimo dycmio dycmoi dmyoic dmyoci dmyioc
dmyico dmycio dmycoi dmoyic dmoyci dmoiyc dmoicy dmociy dmocyi dmioyc dmiocy
dmiyoc dmiyco dmicyo dmicoy dmcoiy dmcoyi dmcioy dmciyo dmcyio dmcyoi domyic
domyci domiyc domicy domciy domcyi doymic doymci doyimc doyicm doycim doycmi
doiymc doiycm doimyc doimcy doicmy doicym docyim docymi dociym docimy docmiy
docmyi dimoyc dimocy dimyoc dimyco dimcyo dimcoy diomyc diomcy dioymc dioycm
diocym diocmy diyomc diyocm diymoc diymco diycmo diycom dicoym dicomy dicyom
dicymo dicmyo dicmoy dcmoiy dcmoyi dcmioy dcmiyo dcmyio dcmyoi dcomiy dcomyi
dcoimy dcoiym dcoyim dcoymi dciomy dcioym dcimoy dcimyo dciymo dciyom dcyoim
dcyomi dcyiom dcyimo dcymio dcymoi

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History of cryptography
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