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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: alrigh
cipher variations:
bmsjhi cntkij douljk epvmkl fqwnlm
grxomn hsypno itzqop juarpq kvbsqr
lwctrs mxdust nyevtu ozfwuv pagxvw
qbhywx rcizxy sdjayz tekbza uflcab
vgmdbc whnecd xiofde yjpgef zkqhfg

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: alrigh
Cipher: zoirts

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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: alrigh

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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: alrigh
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: alrigh
Cipher: nyevtu

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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: alrigh
Cipher: 111324422232

Extended Methods:
Method #1

Plaintext: alrigh
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
a l r i g h 
1 1 2 4 2 3 
1 3 4 2 2 2 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: alrigh
Cipher: armlig

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Method #3

Plaintext: alrigh
method variations:
ahtgmb htgmba tgmbah
gmbaht mbahtg bahtgm

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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: alrigh

all 720 cipher variations:
alrigh alrihg alrgih alrghi alrhgi alrhig alirgh alirhg aligrh alighr alihgr
alihrg algirh algihr algrih algrhi alghri alghir alhigr alhirg alhgir alhgri
alhrgi alhrig arligh arlihg arlgih arlghi arlhgi arlhig arilgh arilhg ariglh
arighl arihgl arihlg argilh argihl arglih arglhi arghli arghil arhigl arhilg
arhgil arhgli arhlgi arhlig airlgh airlhg airglh airghl airhgl airhlg ailrgh
ailrhg ailgrh ailghr ailhgr ailhrg aiglrh aiglhr aigrlh aigrhl aighrl aighlr
aihlgr aihlrg aihglr aihgrl aihrgl aihrlg agrilh agrihl agrlih agrlhi agrhli
agrhil agirlh agirhl agilrh agilhr agihlr agihrl aglirh aglihr aglrih aglrhi
aglhri aglhir aghilr aghirl aghlir aghlri aghrli aghril ahrigl ahrilg ahrgil
ahrgli ahrlgi ahrlig ahirgl ahirlg ahigrl ahiglr ahilgr ahilrg ahgirl ahgilr
ahgril ahgrli ahglri ahglir ahligr ahlirg ahlgir ahlgri ahlrgi ahlrig larigh
larihg largih larghi larhgi larhig lairgh lairhg laigrh laighr laihgr laihrg
lagirh lagihr lagrih lagrhi laghri laghir lahigr lahirg lahgir lahgri lahrgi
lahrig lraigh lraihg lragih lraghi lrahgi lrahig lriagh lriahg lrigah lrigha
lrihga lrihag lrgiah lrgiha lrgaih lrgahi lrghai lrghia lrhiga lrhiag lrhgia
lrhgai lrhagi lrhaig liragh lirahg lirgah lirgha lirhga lirhag liargh liarhg
liagrh liaghr liahgr liahrg ligarh ligahr ligrah ligrha lighra lighar lihagr
liharg lihgar lihgra lihrga lihrag lgriah lgriha lgraih lgrahi lgrhai lgrhia
lgirah lgirha lgiarh lgiahr lgihar lgihra lgairh lgaihr lgarih lgarhi lgahri
lgahir lghiar lghira lghair lghari lghrai lghria lhriga lhriag lhrgia lhrgai
lhragi lhraig lhirga lhirag lhigra lhigar lhiagr lhiarg lhgira lhgiar lhgria
lhgrai lhgari lhgair lhaigr lhairg lhagir lhagri lhargi lharig rlaigh rlaihg
rlagih rlaghi rlahgi rlahig rliagh rliahg rligah rligha rlihga rlihag rlgiah
rlgiha rlgaih rlgahi rlghai rlghia rlhiga rlhiag rlhgia rlhgai rlhagi rlhaig
raligh ralihg ralgih ralghi ralhgi ralhig railgh railhg raiglh raighl raihgl
raihlg ragilh ragihl raglih raglhi raghli raghil rahigl rahilg rahgil rahgli
rahlgi rahlig rialgh rialhg riaglh riaghl riahgl riahlg rilagh rilahg rilgah
rilgha rilhga rilhag riglah riglha rigalh rigahl righal righla rihlga rihlag
rihgla rihgal rihagl rihalg rgailh rgaihl rgalih rgalhi rgahli rgahil rgialh
rgiahl rgilah rgilha rgihla rgihal rgliah rgliha rglaih rglahi rglhai rglhia
rghila rghial rghlia rghlai rghali rghail rhaigl rhailg rhagil rhagli rhalgi
rhalig rhiagl rhialg rhigal rhigla rhilga rhilag rhgial rhgila rhgail rhgali
rhglai rhglia rhliga rhliag rhlgia rhlgai rhlagi rhlaig ilragh ilrahg ilrgah
ilrgha ilrhga ilrhag ilargh ilarhg ilagrh ilaghr ilahgr ilahrg ilgarh ilgahr
ilgrah ilgrha ilghra ilghar ilhagr ilharg ilhgar ilhgra ilhrga ilhrag irlagh
irlahg irlgah irlgha irlhga irlhag iralgh iralhg iraglh iraghl irahgl irahlg
irgalh irgahl irglah irglha irghla irghal irhagl irhalg irhgal irhgla irhlga
irhlag iarlgh iarlhg iarglh iarghl iarhgl iarhlg ialrgh ialrhg ialgrh ialghr
ialhgr ialhrg iaglrh iaglhr iagrlh iagrhl iaghrl iaghlr iahlgr iahlrg iahglr
iahgrl iahrgl iahrlg igralh igrahl igrlah igrlha igrhla igrhal igarlh igarhl
igalrh igalhr igahlr igahrl iglarh iglahr iglrah iglrha iglhra iglhar ighalr
igharl ighlar ighlra ighrla ighral ihragl ihralg ihrgal ihrgla ihrlga ihrlag
ihargl iharlg ihagrl ihaglr ihalgr ihalrg ihgarl ihgalr ihgral ihgrla ihglra
ihglar ihlagr ihlarg ihlgar ihlgra ihlrga ihlrag glriah glriha glraih glrahi
glrhai glrhia glirah glirha gliarh gliahr glihar glihra glairh glaihr glarih
glarhi glahri glahir glhiar glhira glhair glhari glhrai glhria grliah grliha
grlaih grlahi grlhai grlhia grilah grilha grialh griahl grihal grihla grailh
graihl gralih gralhi grahli grahil grhial grhila grhail grhali grhlai grhlia
girlah girlha giralh girahl girhal girhla gilrah gilrha gilarh gilahr gilhar
gilhra gialrh gialhr giarlh giarhl giahrl giahlr gihlar gihlra gihalr giharl
gihral gihrla garilh garihl garlih garlhi garhli garhil gairlh gairhl gailrh
gailhr gaihlr gaihrl galirh galihr galrih galrhi galhri galhir gahilr gahirl
gahlir gahlri gahrli gahril ghrial ghrila ghrail ghrali ghrlai ghrlia ghiral
ghirla ghiarl ghialr ghilar ghilra ghairl ghailr gharil gharli ghalri ghalir
ghliar ghlira ghlair ghlari ghlrai ghlria hlriga hlriag hlrgia hlrgai hlragi
hlraig hlirga hlirag hligra hligar hliagr hliarg hlgira hlgiar hlgria hlgrai
hlgari hlgair hlaigr hlairg hlagir hlagri hlargi hlarig hrliga hrliag hrlgia
hrlgai hrlagi hrlaig hrilga hrilag hrigla hrigal hriagl hrialg hrgila hrgial
hrglia hrglai hrgali hrgail hraigl hrailg hragil hragli hralgi hralig hirlga
hirlag hirgla hirgal hiragl hiralg hilrga hilrag hilgra hilgar hilagr hilarg
higlra higlar higrla higral higarl higalr hialgr hialrg hiaglr hiagrl hiargl
hiarlg hgrila hgrial hgrlia hgrlai hgrali hgrail hgirla hgiral hgilra hgilar
hgialr hgiarl hglira hgliar hglria hglrai hglari hglair hgailr hgairl hgalir
hgalri hgarli hgaril harigl harilg hargil hargli harlgi harlig hairgl hairlg
haigrl haiglr hailgr hailrg hagirl hagilr hagril hagrli haglri haglir haligr
halirg halgir halgri halrgi halrig

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History of cryptography
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