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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: marido
cipher variations:
nbsjep octkfq pdulgr qevmhs rfwnit
sgxoju thypkv uizqlw vjarmx wkbsny
xlctoz ymdupa znevqb aofwrc bpgxsd
cqhyte drizuf esjavg ftkbwh gulcxi
hvmdyj iwnezk jxofal kypgbm lzqhcn

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: marido
Cipher: nzirwl

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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: marido

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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: marido
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: marido
Cipher: znevqb

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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: marido
Cipher: 231124424143

Extended Methods:
Method #1

Plaintext: marido
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
m a r i d o 
2 1 2 4 4 4 
3 1 4 2 1 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: marido
Cipher: brtcil

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Method #3

Plaintext: marido
method variations:
cftrqh ftrqhc trqhcf
rqhcft qhcftr hcftrq

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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: marido

all 720 cipher variations:
marido mariod mardio mardoi marodi maroid mairdo mairod maidro maidor maiodr
maiord madiro madior madrio madroi madori madoir maoidr maoird maodir maodri
maordi maorid mraido mraiod mradio mradoi mraodi mraoid mriado mriaod mridao
mridoa mrioda mrioad mrdiao mrdioa mrdaio mrdaoi mrdoai mrdoia mroida mroiad
mrodia mrodai mroadi mroaid mirado miraod mirdao mirdoa miroda miroad miardo
miarod miadro miador miaodr miaord midaro midaor midrao midroa midora midoar
mioadr mioard miodar miodra miorda miorad mdriao mdrioa mdraio mdraoi mdroai
mdroia mdirao mdiroa mdiaro mdiaor mdioar mdiora mdairo mdaior mdario mdaroi
mdaori mdaoir mdoiar mdoira mdoair mdoari mdorai mdoria morida moriad mordia
mordai moradi moraid moirda moirad moidra moidar moiadr moiard modira modiar
modria modrai modari modair moaidr moaird moadir moadri moardi moarid amrido
amriod amrdio amrdoi amrodi amroid amirdo amirod amidro amidor amiodr amiord
amdiro amdior amdrio amdroi amdori amdoir amoidr amoird amodir amodri amordi
amorid armido armiod armdio armdoi armodi armoid arimdo arimod aridmo aridom
ariodm ariomd ardimo ardiom ardmio ardmoi ardomi ardoim aroidm aroimd arodim
arodmi aromdi aromid airmdo airmod airdmo airdom airodm airomd aimrdo aimrod
aimdro aimdor aimodr aimord aidmro aidmor aidrmo aidrom aidorm aidomr aiomdr
aiomrd aiodmr aiodrm aiordm aiormd adrimo adriom adrmio adrmoi adromi adroim
adirmo adirom adimro adimor adiomr adiorm admiro admior admrio admroi admori
admoir adoimr adoirm adomir adomri adormi adorim aoridm aorimd aordim aordmi
aormdi aormid aoirdm aoirmd aoidrm aoidmr aoimdr aoimrd aodirm aodimr aodrim
aodrmi aodmri aodmir aomidr aomird aomdir aomdri aomrdi aomrid ramido ramiod
ramdio ramdoi ramodi ramoid raimdo raimod raidmo raidom raiodm raiomd radimo
radiom radmio radmoi radomi radoim raoidm raoimd raodim raodmi raomdi raomid
rmaido rmaiod rmadio rmadoi rmaodi rmaoid rmiado rmiaod rmidao rmidoa rmioda
rmioad rmdiao rmdioa rmdaio rmdaoi rmdoai rmdoia rmoida rmoiad rmodia rmodai
rmoadi rmoaid rimado rimaod rimdao rimdoa rimoda rimoad riamdo riamod riadmo
riadom riaodm riaomd ridamo ridaom ridmao ridmoa ridoma ridoam rioadm rioamd
riodam riodma riomda riomad rdmiao rdmioa rdmaio rdmaoi rdmoai rdmoia rdimao
rdimoa rdiamo rdiaom rdioam rdioma rdaimo rdaiom rdamio rdamoi rdaomi rdaoim
rdoiam rdoima rdoaim rdoami rdomai rdomia romida romiad romdia romdai romadi
romaid roimda roimad roidma roidam roiadm roiamd rodima rodiam rodmia rodmai
rodami rodaim roaidm roaimd roadim roadmi roamdi roamid iarmdo iarmod iardmo
iardom iarodm iaromd iamrdo iamrod iamdro iamdor iamodr iamord iadmro iadmor
iadrmo iadrom iadorm iadomr iaomdr iaomrd iaodmr iaodrm iaordm iaormd iramdo
iramod iradmo iradom iraodm iraomd irmado irmaod irmdao irmdoa irmoda irmoad
irdmao irdmoa irdamo irdaom irdoam irdoma iromda iromad irodma irodam iroadm
iroamd imrado imraod imrdao imrdoa imroda imroad imardo imarod imadro imador
imaodr imaord imdaro imdaor imdrao imdroa imdora imdoar imoadr imoard imodar
imodra imorda imorad idrmao idrmoa idramo idraom idroam idroma idmrao idmroa
idmaro idmaor idmoar idmora idamro idamor idarmo idarom idaorm idaomr idomar
idomra idoamr idoarm idoram idorma iormda iormad iordma iordam ioradm ioramd
iomrda iomrad iomdra iomdar iomadr iomard iodmra iodmar iodrma iodram iodarm
iodamr ioamdr ioamrd ioadmr ioadrm ioardm ioarmd darimo dariom darmio darmoi
daromi daroim dairmo dairom daimro daimor daiomr daiorm damiro damior damrio
damroi damori damoir daoimr daoirm daomir daomri daormi daorim draimo draiom
dramio dramoi draomi draoim driamo driaom drimao drimoa drioma drioam drmiao
drmioa drmaio drmaoi drmoai drmoia droima droiam dromia dromai droami droaim
diramo diraom dirmao dirmoa diroma diroam diarmo diarom diamro diamor diaomr
diaorm dimaro dimaor dimrao dimroa dimora dimoar dioamr dioarm diomar diomra
diorma dioram dmriao dmrioa dmraio dmraoi dmroai dmroia dmirao dmiroa dmiaro
dmiaor dmioar dmiora dmairo dmaior dmario dmaroi dmaori dmaoir dmoiar dmoira
dmoair dmoari dmorai dmoria dorima doriam dormia dormai dorami doraim doirma
doiram doimra doimar doiamr doiarm domira domiar domria domrai domari domair
doaimr doairm doamir doamri doarmi doarim oaridm oarimd oardim oardmi oarmdi
oarmid oairdm oairmd oaidrm oaidmr oaimdr oaimrd oadirm oadimr oadrim oadrmi
oadmri oadmir oamidr oamird oamdir oamdri oamrdi oamrid oraidm oraimd oradim
oradmi oramdi oramid oriadm oriamd oridam oridma orimda orimad ordiam ordima
ordaim ordami ordmai ordmia ormida ormiad ormdia ormdai ormadi ormaid oiradm
oiramd oirdam oirdma oirmda oirmad oiardm oiarmd oiadrm oiadmr oiamdr oiamrd
oidarm oidamr oidram oidrma oidmra oidmar oimadr oimard oimdar oimdra oimrda
oimrad odriam odrima odraim odrami odrmai odrmia odiram odirma odiarm odiamr
odimar odimra odairm odaimr odarim odarmi odamri odamir odmiar odmira odmair
odmari odmrai odmria omrida omriad omrdia omrdai omradi omraid omirda omirad
omidra omidar omiadr omiard omdira omdiar omdria omdrai omdari omdair omaidr
omaird omadir omadri omardi omarid

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History of cryptography
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