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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: surfed
cipher variations:
tvsgfe uwthgf vxuihg wyvjih xzwkji
yaxlkj zbymlk acznml bdaonm cebpon
dfcqpo egdrqp fhesrq giftsr hjguts
ikhvut jliwvu kmjxwv lnkyxw molzyx
npmazy oqnbaz procba qspdcb rtqedc

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: surfed
Cipher: hfiuvw

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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: surfed

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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: surfed
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: surfed
Cipher: fhesrq

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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: surfed
Cipher: 345424125141

Extended Methods:
Method #1

Plaintext: surfed
method variations:

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

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Method #3

Plaintext: surfed
method variations:
yidwql idwqly dwqlyi
wqlyid qlyidw lyidwq

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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: surfed

all 720 cipher variations:
surfed surfde surefd suredf surdef surdfe sufred sufrde suferd sufedr sufder
sufdre suefrd suefdr suerfd suerdf suedrf suedfr sudfer sudfre sudefr suderf
sudref sudrfe srufed srufde sruefd sruedf srudef srudfe srfued srfude srfeud
srfedu srfdeu srfdue srefud srefdu sreufd sreudf sreduf sredfu srdfeu srdfue
srdefu srdeuf srduef srdufe sfrued sfrude sfreud sfredu sfrdeu sfrdue sfured
sfurde sfuerd sfuedr sfuder sfudre sfeurd sfeudr sferud sferdu sfedru sfedur
sfduer sfdure sfdeur sfderu sfdreu sfdrue serfud serfdu serufd serudf serduf
serdfu sefrud sefrdu sefurd sefudr sefdur sefdru seufrd seufdr seurfd seurdf
seudrf seudfr sedfur sedfru sedufr sedurf sedruf sedrfu sdrfeu sdrfue sdrefu
sdreuf sdruef sdrufe sdfreu sdfrue sdferu sdfeur sdfuer sdfure sdefru sdefur
sderfu sderuf sdeurf sdeufr sdufer sdufre sduefr sduerf sduref sdurfe usrfed
usrfde usrefd usredf usrdef usrdfe usfred usfrde usferd usfedr usfder usfdre
usefrd usefdr userfd userdf usedrf usedfr usdfer usdfre usdefr usderf usdref
usdrfe ursfed ursfde ursefd ursedf ursdef ursdfe urfsed urfsde urfesd urfeds
urfdes urfdse urefsd urefds uresfd uresdf uredsf uredfs urdfes urdfse urdefs
urdesf urdsef urdsfe ufrsed ufrsde ufresd ufreds ufrdes ufrdse ufsred ufsrde
ufserd ufsedr ufsder ufsdre ufesrd ufesdr ufersd uferds ufedrs ufedsr ufdser
ufdsre ufdesr ufders ufdres ufdrse uerfsd uerfds uersfd uersdf uerdsf uerdfs
uefrsd uefrds uefsrd uefsdr uefdsr uefdrs uesfrd uesfdr uesrfd uesrdf uesdrf
uesdfr uedfsr uedfrs uedsfr uedsrf uedrsf uedrfs udrfes udrfse udrefs udresf
udrsef udrsfe udfres udfrse udfers udfesr udfser udfsre udefrs udefsr uderfs
udersf udesrf udesfr udsfer udsfre udsefr udserf udsref udsrfe rusfed rusfde
rusefd rusedf rusdef rusdfe rufsed rufsde rufesd rufeds rufdes rufdse ruefsd
ruefds ruesfd ruesdf ruedsf ruedfs rudfes rudfse rudefs rudesf rudsef rudsfe
rsufed rsufde rsuefd rsuedf rsudef rsudfe rsfued rsfude rsfeud rsfedu rsfdeu
rsfdue rsefud rsefdu rseufd rseudf rseduf rsedfu rsdfeu rsdfue rsdefu rsdeuf
rsduef rsdufe rfsued rfsude rfseud rfsedu rfsdeu rfsdue rfused rfusde rfuesd
rfueds rfudes rfudse rfeusd rfeuds rfesud rfesdu rfedsu rfedus rfdues rfduse
rfdeus rfdesu rfdseu rfdsue resfud resfdu resufd resudf resduf resdfu refsud
refsdu refusd refuds refdus refdsu reufsd reufds reusfd reusdf reudsf reudfs
redfus redfsu redufs redusf redsuf redsfu rdsfeu rdsfue rdsefu rdseuf rdsuef
rdsufe rdfseu rdfsue rdfesu rdfeus rdfues rdfuse rdefsu rdefus rdesfu rdesuf
rdeusf rdeufs rdufes rdufse rduefs rduesf rdusef rdusfe fursed fursde furesd
fureds furdes furdse fusred fusrde fuserd fusedr fusder fusdre fuesrd fuesdr
fuersd fuerds fuedrs fuedsr fudser fudsre fudesr fuders fudres fudrse frused
frusde fruesd frueds frudes frudse frsued frsude frseud frsedu frsdeu frsdue
fresud fresdu freusd freuds fredus fredsu frdseu frdsue frdesu frdeus frdues
frduse fsrued fsrude fsreud fsredu fsrdeu fsrdue fsured fsurde fsuerd fsuedr
fsuder fsudre fseurd fseudr fserud fserdu fsedru fsedur fsduer fsdure fsdeur
fsderu fsdreu fsdrue fersud fersdu ferusd feruds ferdus ferdsu fesrud fesrdu
fesurd fesudr fesdur fesdru feusrd feusdr feursd feurds feudrs feudsr fedsur
fedsru fedusr fedurs fedrus fedrsu fdrseu fdrsue fdresu fdreus fdrues fdruse
fdsreu fdsrue fdseru fdseur fdsuer fdsure fdesru fdesur fdersu fderus fdeurs
fdeusr fduser fdusre fduesr fduers fdures fdurse eurfsd eurfds eursfd eursdf
eurdsf eurdfs eufrsd eufrds eufsrd eufsdr eufdsr eufdrs eusfrd eusfdr eusrfd
eusrdf eusdrf eusdfr eudfsr eudfrs eudsfr eudsrf eudrsf eudrfs erufsd erufds
erusfd erusdf erudsf erudfs erfusd erfuds erfsud erfsdu erfdsu erfdus ersfud
ersfdu ersufd ersudf ersduf ersdfu erdfsu erdfus erdsfu erdsuf erdusf erdufs
efrusd efruds efrsud efrsdu efrdsu efrdus efursd efurds efusrd efusdr efudsr
efudrs efsurd efsudr efsrud efsrdu efsdru efsdur efdusr efdurs efdsur efdsru
efdrsu efdrus esrfud esrfdu esrufd esrudf esrduf esrdfu esfrud esfrdu esfurd
esfudr esfdur esfdru esufrd esufdr esurfd esurdf esudrf esudfr esdfur esdfru
esdufr esdurf esdruf esdrfu edrfsu edrfus edrsfu edrsuf edrusf edrufs edfrsu
edfrus edfsru edfsur edfusr edfurs edsfru edsfur edsrfu edsruf edsurf edsufr
edufsr edufrs edusfr edusrf edursf edurfs durfes durfse durefs duresf dursef
dursfe dufres dufrse dufers dufesr dufser dufsre duefrs duefsr duerfs duersf
duesrf duesfr dusfer dusfre dusefr duserf dusref dusrfe drufes drufse druefs
druesf drusef drusfe drfues drfuse drfeus drfesu drfseu drfsue drefus drefsu
dreufs dreusf dresuf dresfu drsfeu drsfue drsefu drseuf drsuef drsufe dfrues
dfruse dfreus dfresu dfrseu dfrsue dfures dfurse dfuers dfuesr dfuser dfusre
dfeurs dfeusr dferus dfersu dfesru dfesur dfsuer dfsure dfseur dfseru dfsreu
dfsrue derfus derfsu derufs derusf dersuf dersfu defrus defrsu defurs defusr
defsur defsru deufrs deufsr deurfs deursf deusrf deusfr desfur desfru desufr
desurf desruf desrfu dsrfeu dsrfue dsrefu dsreuf dsruef dsrufe dsfreu dsfrue
dsferu dsfeur dsfuer dsfure dsefru dsefur dserfu dseruf dseurf dseufr dsufer
dsufre dsuefr dsuerf dsuref dsurfe

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History of cryptography
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