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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: spruit
cipher variations:
tqsvju urtwkv vsuxlw wtvymx xuwzny
yvxaoz zwybpa axzcqb byadrc czbesd
dacfte ebdguf fcehvg gdfiwh hegjxi
ifhkyj jgilzk khjmal liknbm mjlocn
nkmpdo olnqep pmorfq qnpsgr roqths

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: spruit
Cipher: hkifrg

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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: spruit

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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: spruit
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: spruit
Cipher: fcehvg

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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: spruit
Cipher: 345324544244

Extended Methods:
Method #1

Plaintext: spruit
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
s p r u i t 
3 5 2 5 4 4 
4 3 4 4 2 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: spruit
Cipher: xwtotr

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Method #3

Plaintext: spruit
method variations:
yhytro hytroy ytroyh
troyhy royhyt oyhytr

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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: spruit

all 720 cipher variations:
spruit spruti spriut spritu sprtiu sprtui spurit spurti spuirt spuitr sputir
sputri spiurt spiutr spirut spirtu spitru spitur sptuir spturi sptiur sptiru
sptriu sptrui srpuit srputi srpiut srpitu srptiu srptui srupit srupti sruipt
sruitp srutip srutpi sriupt sriutp sriput sriptu sritpu sritup srtuip srtupi
srtiup srtipu srtpiu srtpui surpit surpti suript suritp surtip surtpi suprit
suprti supirt supitr suptir suptri suiprt suiptr suirpt suirtp suitrp suitpr
sutpir sutpri sutipr sutirp sutrip sutrpi sirupt sirutp sirput sirptu sirtpu
sirtup siurpt siurtp siuprt siuptr siutpr siutrp sipurt siputr siprut siprtu
siptru siptur situpr siturp sitpur sitpru sitrpu sitrup struip strupi striup
stripu strpiu strpui sturip sturpi stuirp stuipr stupir stupri stiurp stiupr
stirup stirpu stipru stipur stpuir stpuri stpiur stpiru stpriu stprui psruit
psruti psriut psritu psrtiu psrtui psurit psurti psuirt psuitr psutir psutri
psiurt psiutr psirut psirtu psitru psitur pstuir psturi pstiur pstiru pstriu
pstrui prsuit prsuti prsiut prsitu prstiu prstui prusit prusti pruist pruits
prutis prutsi priust priuts prisut pristu pritsu pritus prtuis prtusi prtius
prtisu prtsiu prtsui pursit pursti purist purits purtis purtsi pusrit pusrti
pusirt pusitr pustir pustri puisrt puistr puirst puirts puitrs puitsr putsir
putsri putisr putirs putris putrsi pirust piruts pirsut pirstu pirtsu pirtus
piurst piurts piusrt piustr piutsr piutrs pisurt pisutr pisrut pisrtu pistru
pistur pitusr piturs pitsur pitsru pitrsu pitrus ptruis ptrusi ptrius ptrisu
ptrsiu ptrsui pturis ptursi ptuirs ptuisr ptusir ptusri ptiurs ptiusr ptirus
ptirsu ptisru ptisur ptsuir ptsuri ptsiur ptsiru ptsriu ptsrui rpsuit rpsuti
rpsiut rpsitu rpstiu rpstui rpusit rpusti rpuist rpuits rputis rputsi rpiust
rpiuts rpisut rpistu rpitsu rpitus rptuis rptusi rptius rptisu rptsiu rptsui
rspuit rsputi rspiut rspitu rsptiu rsptui rsupit rsupti rsuipt rsuitp rsutip
rsutpi rsiupt rsiutp rsiput rsiptu rsitpu rsitup rstuip rstupi rstiup rstipu
rstpiu rstpui ruspit ruspti rusipt rusitp rustip rustpi rupsit rupsti rupist
rupits ruptis ruptsi ruipst ruipts ruispt ruistp ruitsp ruitps rutpis rutpsi
rutips rutisp rutsip rutspi risupt risutp risput risptu ristpu ristup riuspt
riustp riupst riupts riutps riutsp ripust riputs ripsut ripstu riptsu riptus
ritups ritusp ritpus ritpsu ritspu ritsup rtsuip rtsupi rtsiup rtsipu rtspiu
rtspui rtusip rtuspi rtuisp rtuips rtupis rtupsi rtiusp rtiups rtisup rtispu
rtipsu rtipus rtpuis rtpusi rtpius rtpisu rtpsiu rtpsui uprsit uprsti uprist
uprits uprtis uprtsi upsrit upsrti upsirt upsitr upstir upstri upisrt upistr
upirst upirts upitrs upitsr uptsir uptsri uptisr uptirs uptris uptrsi urpsit
urpsti urpist urpits urptis urptsi urspit urspti ursipt ursitp urstip urstpi
urispt uristp uripst uripts uritps uritsp urtsip urtspi urtisp urtips urtpis
urtpsi usrpit usrpti usript usritp usrtip usrtpi usprit usprti uspirt uspitr
usptir usptri usiprt usiptr usirpt usirtp usitrp usitpr ustpir ustpri ustipr
ustirp ustrip ustrpi uirspt uirstp uirpst uirpts uirtps uirtsp uisrpt uisrtp
uisprt uisptr uistpr uistrp uipsrt uipstr uiprst uiprts uiptrs uiptsr uitspr
uitsrp uitpsr uitprs uitrps uitrsp utrsip utrspi utrisp utrips utrpis utrpsi
utsrip utsrpi utsirp utsipr utspir utspri utisrp utispr utirsp utirps utiprs
utipsr utpsir utpsri utpisr utpirs utpris utprsi iprust ipruts iprsut iprstu
iprtsu iprtus ipurst ipurts ipusrt ipustr iputsr iputrs ipsurt ipsutr ipsrut
ipsrtu ipstru ipstur iptusr ipturs iptsur iptsru iptrsu iptrus irpust irputs
irpsut irpstu irptsu irptus irupst irupts iruspt irustp irutsp irutps irsupt
irsutp irsput irsptu irstpu irstup irtusp irtups irtsup irtspu irtpsu irtpus
iurpst iurpts iurspt iurstp iurtsp iurtps iuprst iuprts iupsrt iupstr iuptsr
iuptrs iusprt iusptr iusrpt iusrtp iustrp iustpr iutpsr iutprs iutspr iutsrp
iutrsp iutrps isrupt isrutp isrput isrptu isrtpu isrtup isurpt isurtp isuprt
isuptr isutpr isutrp ispurt isputr isprut isprtu isptru isptur istupr isturp
istpur istpru istrpu istrup itrusp itrups itrsup itrspu itrpsu itrpus itursp
iturps itusrp ituspr itupsr ituprs itsurp itsupr itsrup itsrpu itspru itspur
itpusr itpurs itpsur itpsru itprsu itprus tpruis tprusi tprius tprisu tprsiu
tprsui tpuris tpursi tpuirs tpuisr tpusir tpusri tpiurs tpiusr tpirus tpirsu
tpisru tpisur tpsuir tpsuri tpsiur tpsiru tpsriu tpsrui trpuis trpusi trpius
trpisu trpsiu trpsui trupis trupsi truips truisp trusip truspi triups triusp
tripus tripsu trispu trisup trsuip trsupi trsiup trsipu trspiu trspui turpis
turpsi turips turisp tursip turspi tupris tuprsi tupirs tupisr tupsir tupsri
tuiprs tuipsr tuirps tuirsp tuisrp tuispr tuspir tuspri tusipr tusirp tusrip
tusrpi tirups tirusp tirpus tirpsu tirspu tirsup tiurps tiursp tiuprs tiupsr
tiuspr tiusrp tipurs tipusr tiprus tiprsu tipsru tipsur tisupr tisurp tispur
tispru tisrpu tisrup tsruip tsrupi tsriup tsripu tsrpiu tsrpui tsurip tsurpi
tsuirp tsuipr tsupir tsupri tsiurp tsiupr tsirup tsirpu tsipru tsipur tspuir
tspuri tspiur tspiru tspriu tsprui

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History of cryptography
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