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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: vigoda
cipher variations:
wjhpeb xkiqfc yljrgd zmkshe anltif
bomujg cpnvkh dqowli erpxmj fsqynk
gtrzol husapm ivtbqn jwucro kxvdsp
lywetq mzxfur naygvs obzhwt pcaixu
qdbjyv reckzw sfdlax tgemby uhfncz

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: vigoda
Cipher: ertlwz

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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: vigoda

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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: vigoda
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: vigoda
Cipher: ivtbqn

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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: vigoda
Cipher: 154222434111

Extended Methods:
Method #1

Plaintext: vigoda
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
v i g o d a 
1 4 2 4 4 1 
5 2 2 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: vigoda
Cipher: qrdkma

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Method #3

Plaintext: vigoda
method variations:
ugrsaa grsaau rsaaug
saaugr aaugrs augrsa

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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: vigoda

all 720 cipher variations:
vigoda vigoad vigdoa vigdao vigado vigaod viogda viogad viodga viodag vioadg
vioagd vidoga vidoag vidgoa vidgao vidago vidaog viaodg viaogd viadog viadgo
viagdo viagod vgioda vgioad vgidoa vgidao vgiado vgiaod vgoida vgoiad vgodia
vgodai vgoadi vgoaid vgdoia vgdoai vgdioa vgdiao vgdaio vgdaoi vgaodi vgaoid
vgadoi vgadio vgaido vgaiod vogida vogiad vogdia vogdai vogadi vogaid voigda
voigad voidga voidag voiadg voiagd vodiga vodiag vodgia vodgai vodagi vodaig
voaidg voaigd voadig voadgi voagdi voagid vdgoia vdgoai vdgioa vdgiao vdgaio
vdgaoi vdogia vdogai vdoiga vdoiag vdoaig vdoagi vdioga vdioag vdigoa vdigao
vdiago vdiaog vdaoig vdaogi vdaiog vdaigo vdagio vdagoi vagodi vagoid vagdoi
vagdio vagido vagiod vaogdi vaogid vaodgi vaodig vaoidg vaoigd vadogi vadoig
vadgoi vadgio vadigo vadiog vaiodg vaiogd vaidog vaidgo vaigdo vaigod ivgoda
ivgoad ivgdoa ivgdao ivgado ivgaod ivogda ivogad ivodga ivodag ivoadg ivoagd
ivdoga ivdoag ivdgoa ivdgao ivdago ivdaog ivaodg ivaogd ivadog ivadgo ivagdo
ivagod igvoda igvoad igvdoa igvdao igvado igvaod igovda igovad igodva igodav
igoadv igoavd igdova igdoav igdvoa igdvao igdavo igdaov igaodv igaovd igadov
igadvo igavdo igavod iogvda iogvad iogdva iogdav iogadv iogavd iovgda iovgad
iovdga iovdag iovadg iovagd iodvga iodvag iodgva iodgav iodagv iodavg ioavdg
ioavgd ioadvg ioadgv ioagdv ioagvd idgova idgoav idgvoa idgvao idgavo idgaov
idogva idogav idovga idovag idoavg idoagv idvoga idvoag idvgoa idvgao idvago
idvaog idaovg idaogv idavog idavgo idagvo idagov iagodv iagovd iagdov iagdvo
iagvdo iagvod iaogdv iaogvd iaodgv iaodvg iaovdg iaovgd iadogv iadovg iadgov
iadgvo iadvgo iadvog iavodg iavogd iavdog iavdgo iavgdo iavgod givoda givoad
givdoa givdao givado givaod giovda giovad giodva giodav gioadv gioavd gidova
gidoav gidvoa gidvao gidavo gidaov giaodv giaovd giadov giadvo giavdo giavod
gvioda gvioad gvidoa gvidao gviado gviaod gvoida gvoiad gvodia gvodai gvoadi
gvoaid gvdoia gvdoai gvdioa gvdiao gvdaio gvdaoi gvaodi gvaoid gvadoi gvadio
gvaido gvaiod govida goviad govdia govdai govadi govaid goivda goivad goidva
goidav goiadv goiavd godiva godiav godvia godvai godavi godaiv goaidv goaivd
goadiv goadvi goavdi goavid gdvoia gdvoai gdvioa gdviao gdvaio gdvaoi gdovia
gdovai gdoiva gdoiav gdoaiv gdoavi gdiova gdioav gdivoa gdivao gdiavo gdiaov
gdaoiv gdaovi gdaiov gdaivo gdavio gdavoi gavodi gavoid gavdoi gavdio gavido
gaviod gaovdi gaovid gaodvi gaodiv gaoidv gaoivd gadovi gadoiv gadvoi gadvio
gadivo gadiov gaiodv gaiovd gaidov gaidvo gaivdo gaivod oigvda oigvad oigdva
oigdav oigadv oigavd oivgda oivgad oivdga oivdag oivadg oivagd oidvga oidvag
oidgva oidgav oidagv oidavg oiavdg oiavgd oiadvg oiadgv oiagdv oiagvd ogivda
ogivad ogidva ogidav ogiadv ogiavd ogvida ogviad ogvdia ogvdai ogvadi ogvaid
ogdvia ogdvai ogdiva ogdiav ogdaiv ogdavi ogavdi ogavid ogadvi ogadiv ogaidv
ogaivd ovgida ovgiad ovgdia ovgdai ovgadi ovgaid ovigda ovigad ovidga ovidag
oviadg oviagd ovdiga ovdiag ovdgia ovdgai ovdagi ovdaig ovaidg ovaigd ovadig
ovadgi ovagdi ovagid odgvia odgvai odgiva odgiav odgaiv odgavi odvgia odvgai
odviga odviag odvaig odvagi odivga odivag odigva odigav odiagv odiavg odavig
odavgi odaivg odaigv odagiv odagvi oagvdi oagvid oagdvi oagdiv oagidv oagivd
oavgdi oavgid oavdgi oavdig oavidg oavigd oadvgi oadvig oadgvi oadgiv oadigv
oadivg oaivdg oaivgd oaidvg oaidgv oaigdv oaigvd digova digoav digvoa digvao
digavo digaov diogva diogav diovga diovag dioavg dioagv divoga divoag divgoa
divgao divago divaog diaovg diaogv diavog diavgo diagvo diagov dgiova dgioav
dgivoa dgivao dgiavo dgiaov dgoiva dgoiav dgovia dgovai dgoavi dgoaiv dgvoia
dgvoai dgvioa dgviao dgvaio dgvaoi dgaovi dgaoiv dgavoi dgavio dgaivo dgaiov
dogiva dogiav dogvia dogvai dogavi dogaiv doigva doigav doivga doivag doiavg
doiagv doviga doviag dovgia dovgai dovagi dovaig doaivg doaigv doavig doavgi
doagvi doagiv dvgoia dvgoai dvgioa dvgiao dvgaio dvgaoi dvogia dvogai dvoiga
dvoiag dvoaig dvoagi dvioga dvioag dvigoa dvigao dviago dviaog dvaoig dvaogi
dvaiog dvaigo dvagio dvagoi dagovi dagoiv dagvoi dagvio dagivo dagiov daogvi
daogiv daovgi daovig daoivg daoigv davogi davoig davgoi davgio davigo daviog
daiovg daiogv daivog daivgo daigvo daigov aigodv aigovd aigdov aigdvo aigvdo
aigvod aiogdv aiogvd aiodgv aiodvg aiovdg aiovgd aidogv aidovg aidgov aidgvo
aidvgo aidvog aivodg aivogd aivdog aivdgo aivgdo aivgod agiodv agiovd agidov
agidvo agivdo agivod agoidv agoivd agodiv agodvi agovdi agovid agdoiv agdovi
agdiov agdivo agdvio agdvoi agvodi agvoid agvdoi agvdio agvido agviod aogidv
aogivd aogdiv aogdvi aogvdi aogvid aoigdv aoigvd aoidgv aoidvg aoivdg aoivgd
aodigv aodivg aodgiv aodgvi aodvgi aodvig aovidg aovigd aovdig aovdgi aovgdi
aovgid adgoiv adgovi adgiov adgivo adgvio adgvoi adogiv adogvi adoigv adoivg
adovig adovgi adiogv adiovg adigov adigvo adivgo adivog advoig advogi adviog
advigo advgio advgoi avgodi avgoid avgdoi avgdio avgido avgiod avogdi avogid
avodgi avodig avoidg avoigd avdogi avdoig avdgoi avdgio avdigo avdiog aviodg
aviogd avidog avidgo avigdo avigod

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History of cryptography
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