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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: rodham
cipher variations:
speibn tqfjco urgkdp vshleq wtimfr
xujngs yvkoht zwlpiu axmqjv bynrkw
czoslx daptmy ebqunz fcrvoa gdswpb
hetxqc ifuyrd jgvzse khwatf lixbug
mjycvh nkzdwi olaexj pmbfyk qncgzl

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: rodham
Cipher: ilwszn

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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: rodham

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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: rodham
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: rodham
Cipher: ebqunz

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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: rodham
Cipher: 244341321123

Extended Methods:
Method #1

Plaintext: rodham
method variations:

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

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Method #3

Plaintext: rodham
method variations:
tslbfh slbfht lbfhts
bfhtsl fhtslb htslbf

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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: rodham

all 720 cipher variations:
rodham rodhma rodahm rodamh rodmah rodmha rohdam rohdma rohadm rohamd rohmad
rohmda roahdm roahmd roadhm roadmh roamdh roamhd romhad romhda romahd romadh
romdah romdha rdoham rdohma rdoahm rdoamh rdomah rdomha rdhoam rdhoma rdhaom
rdhamo rdhmao rdhmoa rdahom rdahmo rdaohm rdaomh rdamoh rdamho rdmhao rdmhoa
rdmaho rdmaoh rdmoah rdmoha rhdoam rhdoma rhdaom rhdamo rhdmao rhdmoa rhodam
rhodma rhoadm rhoamd rhomad rhomda rhaodm rhaomd rhadom rhadmo rhamdo rhamod
rhmoad rhmoda rhmaod rhmado rhmdao rhmdoa radhom radhmo radohm radomh radmoh
radmho rahdom rahdmo rahodm rahomd rahmod rahmdo raohdm raohmd raodhm raodmh
raomdh raomhd ramhod ramhdo ramohd ramodh ramdoh ramdho rmdhao rmdhoa rmdaho
rmdaoh rmdoah rmdoha rmhdao rmhdoa rmhado rmhaod rmhoad rmhoda rmahdo rmahod
rmadho rmadoh rmaodh rmaohd rmohad rmohda rmoahd rmoadh rmodah rmodha ordham
ordhma ordahm ordamh ordmah ordmha orhdam orhdma orhadm orhamd orhmad orhmda
orahdm orahmd oradhm oradmh oramdh oramhd ormhad ormhda ormahd ormadh ormdah
ormdha odrham odrhma odrahm odramh odrmah odrmha odhram odhrma odharm odhamr
odhmar odhmra odahrm odahmr odarhm odarmh odamrh odamhr odmhar odmhra odmahr
odmarh odmrah odmrha ohdram ohdrma ohdarm ohdamr ohdmar ohdmra ohrdam ohrdma
ohradm ohramd ohrmad ohrmda ohardm oharmd ohadrm ohadmr ohamdr ohamrd ohmrad
ohmrda ohmard ohmadr ohmdar ohmdra oadhrm oadhmr oadrhm oadrmh oadmrh oadmhr
oahdrm oahdmr oahrdm oahrmd oahmrd oahmdr oarhdm oarhmd oardhm oardmh oarmdh
oarmhd oamhrd oamhdr oamrhd oamrdh oamdrh oamdhr omdhar omdhra omdahr omdarh
omdrah omdrha omhdar omhdra omhadr omhard omhrad omhrda omahdr omahrd omadhr
omadrh omardh omarhd omrhad omrhda omrahd omradh omrdah omrdha dorham dorhma
dorahm doramh dormah dormha dohram dohrma doharm dohamr dohmar dohmra doahrm
doahmr doarhm doarmh doamrh doamhr domhar domhra domahr domarh domrah domrha
droham drohma droahm droamh dromah dromha drhoam drhoma drhaom drhamo drhmao
drhmoa drahom drahmo draohm draomh dramoh dramho drmhao drmhoa drmaho drmaoh
drmoah drmoha dhroam dhroma dhraom dhramo dhrmao dhrmoa dhoram dhorma dhoarm
dhoamr dhomar dhomra dhaorm dhaomr dharom dharmo dhamro dhamor dhmoar dhmora
dhmaor dhmaro dhmrao dhmroa darhom darhmo darohm daromh darmoh darmho dahrom
dahrmo dahorm dahomr dahmor dahmro daohrm daohmr daorhm daormh daomrh daomhr
damhor damhro damohr damorh damroh damrho dmrhao dmrhoa dmraho dmraoh dmroah
dmroha dmhrao dmhroa dmharo dmhaor dmhoar dmhora dmahro dmahor dmarho dmaroh
dmaorh dmaohr dmohar dmohra dmoahr dmoarh dmorah dmorha hodram hodrma hodarm
hodamr hodmar hodmra hordam hordma horadm horamd hormad hormda hoardm hoarmd
hoadrm hoadmr hoamdr hoamrd homrad homrda homard homadr homdar homdra hdoram
hdorma hdoarm hdoamr hdomar hdomra hdroam hdroma hdraom hdramo hdrmao hdrmoa
hdarom hdarmo hdaorm hdaomr hdamor hdamro hdmrao hdmroa hdmaro hdmaor hdmoar
hdmora hrdoam hrdoma hrdaom hrdamo hrdmao hrdmoa hrodam hrodma hroadm hroamd
hromad hromda hraodm hraomd hradom hradmo hramdo hramod hrmoad hrmoda hrmaod
hrmado hrmdao hrmdoa hadrom hadrmo hadorm hadomr hadmor hadmro hardom hardmo
harodm haromd harmod harmdo haordm haormd haodrm haodmr haomdr haomrd hamrod
hamrdo hamord hamodr hamdor hamdro hmdrao hmdroa hmdaro hmdaor hmdoar hmdora
hmrdao hmrdoa hmrado hmraod hmroad hmroda hmardo hmarod hmadro hmador hmaodr
hmaord hmorad hmorda hmoard hmoadr hmodar hmodra aodhrm aodhmr aodrhm aodrmh
aodmrh aodmhr aohdrm aohdmr aohrdm aohrmd aohmrd aohmdr aorhdm aorhmd aordhm
aordmh aormdh aormhd aomhrd aomhdr aomrhd aomrdh aomdrh aomdhr adohrm adohmr
adorhm adormh adomrh adomhr adhorm adhomr adhrom adhrmo adhmro adhmor adrhom
adrhmo adrohm adromh adrmoh adrmho admhro admhor admrho admroh admorh admohr
ahdorm ahdomr ahdrom ahdrmo ahdmro ahdmor ahodrm ahodmr ahordm ahormd ahomrd
ahomdr ahrodm ahromd ahrdom ahrdmo ahrmdo ahrmod ahmord ahmodr ahmrod ahmrdo
ahmdro ahmdor ardhom ardhmo ardohm ardomh ardmoh ardmho arhdom arhdmo arhodm
arhomd arhmod arhmdo arohdm arohmd arodhm arodmh aromdh aromhd armhod armhdo
armohd armodh armdoh armdho amdhro amdhor amdrho amdroh amdorh amdohr amhdro
amhdor amhrdo amhrod amhord amhodr amrhdo amrhod amrdho amrdoh amrodh amrohd
amohrd amohdr amorhd amordh amodrh amodhr modhar modhra modahr modarh modrah
modrha mohdar mohdra mohadr mohard mohrad mohrda moahdr moahrd moadhr moadrh
moardh moarhd morhad morhda morahd moradh mordah mordha mdohar mdohra mdoahr
mdoarh mdorah mdorha mdhoar mdhora mdhaor mdharo mdhrao mdhroa mdahor mdahro
mdaohr mdaorh mdaroh mdarho mdrhao mdrhoa mdraho mdraoh mdroah mdroha mhdoar
mhdora mhdaor mhdaro mhdrao mhdroa mhodar mhodra mhoadr mhoard mhorad mhorda
mhaodr mhaord mhador mhadro mhardo mharod mhroad mhroda mhraod mhrado mhrdao
mhrdoa madhor madhro madohr madorh madroh madrho mahdor mahdro mahodr mahord
mahrod mahrdo maohdr maohrd maodhr maodrh maordh maorhd marhod marhdo marohd
marodh mardoh mardho mrdhao mrdhoa mrdaho mrdaoh mrdoah mrdoha mrhdao mrhdoa
mrhado mrhaod mrhoad mrhoda mrahdo mrahod mradho mradoh mraodh mraohd mrohad
mrohda mroahd mroadh mrodah mrodha

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History of cryptography
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