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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: durfey
cipher variations:
evsgfz fwthga gxuihb hyvjic izwkjd
jaxlke kbymlf lcznmg mdaonh nebpoi
ofcqpj pgdrqk qhesrl riftsm sjgutn
tkhvuo uliwvp vmjxwq wnkyxr xolzys
ypmazt zqnbau arocbv bspdcw ctqedx

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: durfey
Cipher: wfiuvb

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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: durfey

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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: durfey
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: durfey
Cipher: qhesrl

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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: durfey
Cipher: 415424125145

Extended Methods:
Method #1

Plaintext: durfey
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
d u r f e y 
4 5 2 1 5 4 
1 4 4 2 1 5 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: durfey
Cipher: ybuqiv

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Method #3

Plaintext: durfey
method variations:
vidwqu idwquv dwquvi
wquvid quvidw uvidwq

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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: durfey

all 720 cipher variations:
durfey durfye durefy dureyf duryef duryfe dufrey dufrye dufery dufeyr dufyer
dufyre duefry duefyr duerfy dueryf dueyrf dueyfr duyfer duyfre duyefr duyerf
duyref duyrfe drufey drufye druefy drueyf druyef druyfe drfuey drfuye drfeuy
drfeyu drfyeu drfyue drefuy drefyu dreufy dreuyf dreyuf dreyfu dryfeu dryfue
dryefu dryeuf dryuef dryufe dfruey dfruye dfreuy dfreyu dfryeu dfryue dfurey
dfurye dfuery dfueyr dfuyer dfuyre dfeury dfeuyr dferuy dferyu dfeyru dfeyur
dfyuer dfyure dfyeur dfyeru dfyreu dfyrue derfuy derfyu derufy deruyf deryuf
deryfu defruy defryu defury defuyr defyur defyru deufry deufyr deurfy deuryf
deuyrf deuyfr deyfur deyfru deyufr deyurf deyruf deyrfu dyrfeu dyrfue dyrefu
dyreuf dyruef dyrufe dyfreu dyfrue dyferu dyfeur dyfuer dyfure dyefru dyefur
dyerfu dyeruf dyeurf dyeufr dyufer dyufre dyuefr dyuerf dyuref dyurfe udrfey
udrfye udrefy udreyf udryef udryfe udfrey udfrye udfery udfeyr udfyer udfyre
udefry udefyr uderfy uderyf udeyrf udeyfr udyfer udyfre udyefr udyerf udyref
udyrfe urdfey urdfye urdefy urdeyf urdyef urdyfe urfdey urfdye urfedy urfeyd
urfyed urfyde urefdy urefyd uredfy uredyf ureydf ureyfd uryfed uryfde uryefd
uryedf urydef urydfe ufrdey ufrdye ufredy ufreyd ufryed ufryde ufdrey ufdrye
ufdery ufdeyr ufdyer ufdyre ufedry ufedyr uferdy uferyd ufeyrd ufeydr ufyder
ufydre ufyedr ufyerd ufyred ufyrde uerfdy uerfyd uerdfy uerdyf uerydf ueryfd
uefrdy uefryd uefdry uefdyr uefydr uefyrd uedfry uedfyr uedrfy uedryf uedyrf
uedyfr ueyfdr ueyfrd ueydfr ueydrf ueyrdf ueyrfd uyrfed uyrfde uyrefd uyredf
uyrdef uyrdfe uyfred uyfrde uyferd uyfedr uyfder uyfdre uyefrd uyefdr uyerfd
uyerdf uyedrf uyedfr uydfer uydfre uydefr uyderf uydref uydrfe rudfey rudfye
rudefy rudeyf rudyef rudyfe rufdey rufdye rufedy rufeyd rufyed rufyde ruefdy
ruefyd ruedfy ruedyf rueydf rueyfd ruyfed ruyfde ruyefd ruyedf ruydef ruydfe
rdufey rdufye rduefy rdueyf rduyef rduyfe rdfuey rdfuye rdfeuy rdfeyu rdfyeu
rdfyue rdefuy rdefyu rdeufy rdeuyf rdeyuf rdeyfu rdyfeu rdyfue rdyefu rdyeuf
rdyuef rdyufe rfduey rfduye rfdeuy rfdeyu rfdyeu rfdyue rfudey rfudye rfuedy
rfueyd rfuyed rfuyde rfeudy rfeuyd rfeduy rfedyu rfeydu rfeyud rfyued rfyude
rfyeud rfyedu rfydeu rfydue redfuy redfyu redufy reduyf redyuf redyfu refduy
refdyu refudy refuyd refyud refydu reufdy reufyd reudfy reudyf reuydf reuyfd
reyfud reyfdu reyufd reyudf reyduf reydfu rydfeu rydfue rydefu rydeuf ryduef
rydufe ryfdeu ryfdue ryfedu ryfeud ryfued ryfude ryefdu ryefud ryedfu ryeduf
ryeudf ryeufd ryufed ryufde ryuefd ryuedf ryudef ryudfe furdey furdye furedy
fureyd furyed furyde fudrey fudrye fudery fudeyr fudyer fudyre fuedry fuedyr
fuerdy fueryd fueyrd fueydr fuyder fuydre fuyedr fuyerd fuyred fuyrde frudey
frudye fruedy frueyd fruyed fruyde frduey frduye frdeuy frdeyu frdyeu frdyue
freduy fredyu freudy freuyd freyud freydu frydeu frydue fryedu fryeud fryued
fryude fdruey fdruye fdreuy fdreyu fdryeu fdryue fdurey fdurye fduery fdueyr
fduyer fduyre fdeury fdeuyr fderuy fderyu fdeyru fdeyur fdyuer fdyure fdyeur
fdyeru fdyreu fdyrue ferduy ferdyu ferudy feruyd feryud ferydu fedruy fedryu
fedury feduyr fedyur fedyru feudry feudyr feurdy feuryd feuyrd feuydr feydur
feydru feyudr feyurd feyrud feyrdu fyrdeu fyrdue fyredu fyreud fyrued fyrude
fydreu fydrue fyderu fydeur fyduer fydure fyedru fyedur fyerdu fyerud fyeurd
fyeudr fyuder fyudre fyuedr fyuerd fyured fyurde eurfdy eurfyd eurdfy eurdyf
eurydf euryfd eufrdy eufryd eufdry eufdyr eufydr eufyrd eudfry eudfyr eudrfy
eudryf eudyrf eudyfr euyfdr euyfrd euydfr euydrf euyrdf euyrfd erufdy erufyd
erudfy erudyf eruydf eruyfd erfudy erfuyd erfduy erfdyu erfydu erfyud erdfuy
erdfyu erdufy erduyf erdyuf erdyfu eryfdu eryfud erydfu eryduf eryudf eryufd
efrudy efruyd efrduy efrdyu efrydu efryud efurdy efuryd efudry efudyr efuydr
efuyrd efdury efduyr efdruy efdryu efdyru efdyur efyudr efyurd efydur efydru
efyrdu efyrud edrfuy edrfyu edrufy edruyf edryuf edryfu edfruy edfryu edfury
edfuyr edfyur edfyru edufry edufyr edurfy eduryf eduyrf eduyfr edyfur edyfru
edyufr edyurf edyruf edyrfu eyrfdu eyrfud eyrdfu eyrduf eyrudf eyrufd eyfrdu
eyfrud eyfdru eyfdur eyfudr eyfurd eydfru eydfur eydrfu eydruf eydurf eydufr
eyufdr eyufrd eyudfr eyudrf eyurdf eyurfd yurfed yurfde yurefd yuredf yurdef
yurdfe yufred yufrde yuferd yufedr yufder yufdre yuefrd yuefdr yuerfd yuerdf
yuedrf yuedfr yudfer yudfre yudefr yuderf yudref yudrfe yrufed yrufde yruefd
yruedf yrudef yrudfe yrfued yrfude yrfeud yrfedu yrfdeu yrfdue yrefud yrefdu
yreufd yreudf yreduf yredfu yrdfeu yrdfue yrdefu yrdeuf yrduef yrdufe yfrued
yfrude yfreud yfredu yfrdeu yfrdue yfured yfurde yfuerd yfuedr yfuder yfudre
yfeurd yfeudr yferud yferdu yfedru yfedur yfduer yfdure yfdeur yfderu yfdreu
yfdrue yerfud yerfdu yerufd yerudf yerduf yerdfu yefrud yefrdu yefurd yefudr
yefdur yefdru yeufrd yeufdr yeurfd yeurdf yeudrf yeudfr yedfur yedfru yedufr
yedurf yedruf yedrfu ydrfeu ydrfue ydrefu ydreuf ydruef ydrufe ydfreu ydfrue
ydferu ydfeur ydfuer ydfure ydefru ydefur yderfu yderuf ydeurf ydeufr ydufer
ydufre yduefr yduerf yduref ydurfe

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History of cryptography
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