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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: licorn
cipher variations:
mjdpso nkeqtp olfruq pmgsvr qnhtws
roiuxt spjvyu tqkwzv urlxaw vsmybx
wtnzcy xuoadz yvpbea zwqcfb axrdgc
bysehd cztfie daugjf ebvhkg fcwilh
gdxjmi heyknj ifzlok jgampl khbnqm

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: licorn
Cipher: orxlim

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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: licorn

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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: licorn
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: licorn
Cipher: yvpbea

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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: licorn
Cipher: 134231432433

Extended Methods:
Method #1

Plaintext: licorn
method variations:

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

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Method #3

Plaintext: licorn
method variations:
smqhoc mqhocs qhocsm
hocsmq ocsmqh csmqho

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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: licorn

all 720 cipher variations:
licorn liconr licron licrno licnro licnor liocrn liocnr liorcn liornc lionrc
lioncr lirocn lironc lircon lircno lirnco lirnoc linorc linocr linroc linrco
lincro lincor lciorn lcionr lciron lcirno lcinro lcinor lcoirn lcoinr lcorin
lcorni lconri lconir lcroin lcroni lcrion lcrino lcrnio lcrnoi lcnori lcnoir
lcnroi lcnrio lcniro lcnior locirn locinr locrin locrni locnri locnir loicrn
loicnr loircn loirnc loinrc loincr loricn lorinc lorcin lorcni lornci lornic
lonirc lonicr lonric lonrci loncri loncir lrcoin lrconi lrcion lrcino lrcnio
lrcnoi lrocin lrocni lroicn lroinc lronic lronci lriocn lrionc lricon lricno
lrinco lrinoc lrnoic lrnoci lrnioc lrnico lrncio lrncoi lncori lncoir lncroi
lncrio lnciro lncior lnocri lnocir lnorci lnoric lnoirc lnoicr lnroci lnroic
lnrcoi lnrcio lnrico lnrioc lniorc lniocr lniroc lnirco lnicro lnicor ilcorn
ilconr ilcron ilcrno ilcnro ilcnor ilocrn ilocnr ilorcn ilornc ilonrc iloncr
ilrocn ilronc ilrcon ilrcno ilrnco ilrnoc ilnorc ilnocr ilnroc ilnrco ilncro
ilncor iclorn iclonr iclron iclrno iclnro iclnor icolrn icolnr icorln icornl
iconrl iconlr icroln icronl icrlon icrlno icrnlo icrnol icnorl icnolr icnrol
icnrlo icnlro icnlor ioclrn ioclnr iocrln iocrnl iocnrl iocnlr iolcrn iolcnr
iolrcn iolrnc iolnrc iolncr iorlcn iorlnc iorcln iorcnl iorncl iornlc ionlrc
ionlcr ionrlc ionrcl ioncrl ionclr ircoln irconl irclon irclno ircnlo ircnol
irocln irocnl irolcn irolnc ironlc ironcl irlocn irlonc irlcon irlcno irlnco
irlnoc irnolc irnocl irnloc irnlco irnclo irncol incorl incolr incrol incrlo
inclro inclor inocrl inoclr inorcl inorlc inolrc inolcr inrocl inrolc inrcol
inrclo inrlco inrloc inlorc inlocr inlroc inlrco inlcro inlcor cilorn cilonr
cilron cilrno cilnro cilnor ciolrn ciolnr ciorln ciornl cionrl cionlr ciroln
cironl cirlon cirlno cirnlo cirnol cinorl cinolr cinrol cinrlo cinlro cinlor
cliorn clionr cliron clirno clinro clinor cloirn cloinr clorin clorni clonri
clonir clroin clroni clrion clrino clrnio clrnoi clnori clnoir clnroi clnrio
clniro clnior colirn colinr colrin colrni colnri colnir coilrn coilnr coirln
coirnl coinrl coinlr coriln corinl corlin corlni cornli cornil conirl conilr
conril conrli conlri conlir crloin crloni crlion crlino crlnio crlnoi crolin
crolni croiln croinl cronil cronli crioln crionl crilon crilno crinlo crinol
crnoil crnoli crniol crnilo crnlio crnloi cnlori cnloir cnlroi cnlrio cnliro
cnlior cnolri cnolir cnorli cnoril cnoirl cnoilr cnroli cnroil cnrloi cnrlio
cnrilo cnriol cniorl cniolr cnirol cnirlo cnilro cnilor oiclrn oiclnr oicrln
oicrnl oicnrl oicnlr oilcrn oilcnr oilrcn oilrnc oilnrc oilncr oirlcn oirlnc
oircln oircnl oirncl oirnlc oinlrc oinlcr oinrlc oinrcl oincrl oinclr ocilrn
ocilnr ocirln ocirnl ocinrl ocinlr oclirn oclinr oclrin oclrni oclnri oclnir
ocrlin ocrlni ocriln ocrinl ocrnil ocrnli ocnlri ocnlir ocnrli ocnril ocnirl
ocnilr olcirn olcinr olcrin olcrni olcnri olcnir olicrn olicnr olircn olirnc
olinrc olincr olricn olrinc olrcin olrcni olrnci olrnic olnirc olnicr olnric
olnrci olncri olncir orclin orclni orciln orcinl orcnil orcnli orlcin orlcni
orlicn orlinc orlnic orlnci orilcn orilnc oricln oricnl orincl orinlc ornlic
ornlci ornilc ornicl orncil orncli onclri onclir oncrli oncril oncirl oncilr
onlcri onlcir onlrci onlric onlirc onlicr onrlci onrlic onrcli onrcil onricl
onrilc onilrc onilcr onirlc onircl onicrl oniclr ricoln riconl riclon riclno
ricnlo ricnol riocln riocnl riolcn riolnc rionlc rioncl rilocn rilonc rilcon
rilcno rilnco rilnoc rinolc rinocl rinloc rinlco rinclo rincol rcioln rcionl
rcilon rcilno rcinlo rcinol rcoiln rcoinl rcolin rcolni rconli rconil rcloin
rcloni rclion rclino rclnio rclnoi rcnoli rcnoil rcnloi rcnlio rcnilo rcniol
rociln rocinl roclin roclni rocnli rocnil roicln roicnl roilcn roilnc roinlc
roincl rolicn rolinc rolcin rolcni rolnci rolnic ronilc ronicl ronlic ronlci
roncli roncil rlcoin rlconi rlcion rlcino rlcnio rlcnoi rlocin rlocni rloicn
rloinc rlonic rlonci rliocn rlionc rlicon rlicno rlinco rlinoc rlnoic rlnoci
rlnioc rlnico rlncio rlncoi rncoli rncoil rncloi rnclio rncilo rnciol rnocli
rnocil rnolci rnolic rnoilc rnoicl rnloci rnloic rnlcoi rnlcio rnlico rnlioc
rniolc rniocl rniloc rnilco rniclo rnicol nicorl nicolr nicrol nicrlo niclro
niclor niocrl nioclr niorcl niorlc niolrc niolcr nirocl nirolc nircol nirclo
nirlco nirloc nilorc nilocr nilroc nilrco nilcro nilcor nciorl nciolr ncirol
ncirlo ncilro ncilor ncoirl ncoilr ncoril ncorli ncolri ncolir ncroil ncroli
ncriol ncrilo ncrlio ncrloi nclori ncloir nclroi nclrio ncliro nclior nocirl
nocilr nocril nocrli noclri noclir noicrl noiclr noircl noirlc noilrc noilcr
noricl norilc norcil norcli norlci norlic nolirc nolicr nolric nolrci nolcri
nolcir nrcoil nrcoli nrciol nrcilo nrclio nrcloi nrocil nrocli nroicl nroilc
nrolic nrolci nriocl nriolc nricol nriclo nrilco nriloc nrloic nrloci nrlioc
nrlico nrlcio nrlcoi nlcori nlcoir nlcroi nlcrio nlciro nlcior nlocri nlocir
nlorci nloric nloirc nloicr nlroci nlroic nlrcoi nlrcio nlrico nlrioc nliorc
nliocr nliroc nlirco nlicro nlicor

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History of cryptography
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