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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: vibart
cipher variations:
wjcbsu xkdctv yleduw zmfevx angfwy
bohgxz cpihya dqjizb erkjac fslkbd
gtmlce hunmdf ivoneg jwpofh kxqpgi
lyrqhj mzsrik natsjl obutkm pcvuln
qdwvmo rexwnp sfyxoq tgzypr uhazqs

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: vibart
Cipher: eryzig

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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: vibart

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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: vibart
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: vibart
Cipher: ivoneg

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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: vibart
Cipher: 154221112444

Extended Methods:
Method #1

Plaintext: vibart
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 b a r t 
1 4 2 1 2 4 
5 2 1 1 4 4 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: vibart
Cipher: qbrkat

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Method #3

Plaintext: vibart
method variations:
ugaftd gaftdu aftdug
ftduga tdugaf dugaft

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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: vibart

all 720 cipher variations:
vibart vibatr vibrat vibrta vibtra vibtar viabrt viabtr viarbt viartb viatrb
viatbr virabt viratb virbat virbta virtba virtab vitarb vitabr vitrab vitrba
vitbra vitbar vbiart vbiatr vbirat vbirta vbitra vbitar vbairt vbaitr vbarit
vbarti vbatri vbatir vbrait vbrati vbriat vbrita vbrtia vbrtai vbtari vbtair
vbtrai vbtria vbtira vbtiar vabirt vabitr vabrit vabrti vabtri vabtir vaibrt
vaibtr vairbt vairtb vaitrb vaitbr varibt varitb varbit varbti vartbi vartib
vatirb vatibr vatrib vatrbi vatbri vatbir vrbait vrbati vrbiat vrbita vrbtia
vrbtai vrabit vrabti vraibt vraitb vratib vratbi vriabt vriatb vribat vribta
vritba vritab vrtaib vrtabi vrtiab vrtiba vrtbia vrtbai vtbari vtbair vtbrai
vtbria vtbira vtbiar vtabri vtabir vtarbi vtarib vtairb vtaibr vtrabi vtraib
vtrbai vtrbia vtriba vtriab vtiarb vtiabr vtirab vtirba vtibra vtibar ivbart
ivbatr ivbrat ivbrta ivbtra ivbtar ivabrt ivabtr ivarbt ivartb ivatrb ivatbr
ivrabt ivratb ivrbat ivrbta ivrtba ivrtab ivtarb ivtabr ivtrab ivtrba ivtbra
ivtbar ibvart ibvatr ibvrat ibvrta ibvtra ibvtar ibavrt ibavtr ibarvt ibartv
ibatrv ibatvr ibravt ibratv ibrvat ibrvta ibrtva ibrtav ibtarv ibtavr ibtrav
ibtrva ibtvra ibtvar iabvrt iabvtr iabrvt iabrtv iabtrv iabtvr iavbrt iavbtr
iavrbt iavrtb iavtrb iavtbr iarvbt iarvtb iarbvt iarbtv iartbv iartvb iatvrb
iatvbr iatrvb iatrbv iatbrv iatbvr irbavt irbatv irbvat irbvta irbtva irbtav
irabvt irabtv iravbt iravtb iratvb iratbv irvabt irvatb irvbat irvbta irvtba
irvtab irtavb irtabv irtvab irtvba irtbva irtbav itbarv itbavr itbrav itbrva
itbvra itbvar itabrv itabvr itarbv itarvb itavrb itavbr itrabv itravb itrbav
itrbva itrvba itrvab itvarb itvabr itvrab itvrba itvbra itvbar bivart bivatr
bivrat bivrta bivtra bivtar biavrt biavtr biarvt biartv biatrv biatvr biravt
biratv birvat birvta birtva birtav bitarv bitavr bitrav bitrva bitvra bitvar
bviart bviatr bvirat bvirta bvitra bvitar bvairt bvaitr bvarit bvarti bvatri
bvatir bvrait bvrati bvriat bvrita bvrtia bvrtai bvtari bvtair bvtrai bvtria
bvtira bvtiar bavirt bavitr bavrit bavrti bavtri bavtir baivrt baivtr bairvt
bairtv baitrv baitvr barivt baritv barvit barvti bartvi bartiv batirv bativr
batriv batrvi batvri batvir brvait brvati brviat brvita brvtia brvtai bravit
bravti braivt braitv brativ bratvi briavt briatv brivat brivta britva britav
brtaiv brtavi brtiav brtiva brtvia brtvai btvari btvair btvrai btvria btvira
btviar btavri btavir btarvi btariv btairv btaivr btravi btraiv btrvai btrvia
btriva btriav btiarv btiavr btirav btirva btivra btivar aibvrt aibvtr aibrvt
aibrtv aibtrv aibtvr aivbrt aivbtr aivrbt aivrtb aivtrb aivtbr airvbt airvtb
airbvt airbtv airtbv airtvb aitvrb aitvbr aitrvb aitrbv aitbrv aitbvr abivrt
abivtr abirvt abirtv abitrv abitvr abvirt abvitr abvrit abvrti abvtri abvtir
abrvit abrvti abrivt abritv abrtiv abrtvi abtvri abtvir abtrvi abtriv abtirv
abtivr avbirt avbitr avbrit avbrti avbtri avbtir avibrt avibtr avirbt avirtb
avitrb avitbr avribt avritb avrbit avrbti avrtbi avrtib avtirb avtibr avtrib
avtrbi avtbri avtbir arbvit arbvti arbivt arbitv arbtiv arbtvi arvbit arvbti
arvibt arvitb arvtib arvtbi arivbt arivtb aribvt aribtv aritbv aritvb artvib
artvbi artivb artibv artbiv artbvi atbvri atbvir atbrvi atbriv atbirv atbivr
atvbri atvbir atvrbi atvrib atvirb atvibr atrvbi atrvib atrbvi atrbiv atribv
atrivb ativrb ativbr atirvb atirbv atibrv atibvr ribavt ribatv ribvat ribvta
ribtva ribtav riabvt riabtv riavbt riavtb riatvb riatbv rivabt rivatb rivbat
rivbta rivtba rivtab ritavb ritabv ritvab ritvba ritbva ritbav rbiavt rbiatv
rbivat rbivta rbitva rbitav rbaivt rbaitv rbavit rbavti rbatvi rbativ rbvait
rbvati rbviat rbvita rbvtia rbvtai rbtavi rbtaiv rbtvai rbtvia rbtiva rbtiav
rabivt rabitv rabvit rabvti rabtvi rabtiv raibvt raibtv raivbt raivtb raitvb
raitbv ravibt ravitb ravbit ravbti ravtbi ravtib rativb ratibv ratvib ratvbi
ratbvi ratbiv rvbait rvbati rvbiat rvbita rvbtia rvbtai rvabit rvabti rvaibt
rvaitb rvatib rvatbi rviabt rviatb rvibat rvibta rvitba rvitab rvtaib rvtabi
rvtiab rvtiba rvtbia rvtbai rtbavi rtbaiv rtbvai rtbvia rtbiva rtbiav rtabvi
rtabiv rtavbi rtavib rtaivb rtaibv rtvabi rtvaib rtvbai rtvbia rtviba rtviab
rtiavb rtiabv rtivab rtivba rtibva rtibav tibarv tibavr tibrav tibrva tibvra
tibvar tiabrv tiabvr tiarbv tiarvb tiavrb tiavbr tirabv tiravb tirbav tirbva
tirvba tirvab tivarb tivabr tivrab tivrba tivbra tivbar tbiarv tbiavr tbirav
tbirva tbivra tbivar tbairv tbaivr tbariv tbarvi tbavri tbavir tbraiv tbravi
tbriav tbriva tbrvia tbrvai tbvari tbvair tbvrai tbvria tbvira tbviar tabirv
tabivr tabriv tabrvi tabvri tabvir taibrv taibvr tairbv tairvb taivrb taivbr
taribv tarivb tarbiv tarbvi tarvbi tarvib tavirb tavibr tavrib tavrbi tavbri
tavbir trbaiv trbavi trbiav trbiva trbvia trbvai trabiv trabvi traibv traivb
travib travbi triabv triavb tribav tribva trivba trivab trvaib trvabi trviab
trviba trvbia trvbai tvbari tvbair tvbrai tvbria tvbira tvbiar tvabri tvabir
tvarbi tvarib tvairb tvaibr tvrabi tvraib tvrbai tvrbia tvriba tvriab tviarb
tviabr tvirab tvirba tvibra tvibar

Read more ...[1] , [2] , [3]

History of cryptography
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