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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: avonde
cipher variations:
bwpoef cxqpfg dyrqgh ezsrhi fatsij
gbutjk hcvukl idwvlm jexwmn kfyxno
lgzyop mhazpq nibaqr ojcbrs pkdcst
qledtu rmfeuv sngfvw tohgwx upihxy
vqjiyz wrkjza xslkab ytmlbc zunmcd

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: avonde
Cipher: zelmwv

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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: avonde

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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: avonde
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: avonde
Cipher: nibaqr

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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: avonde
Cipher: 111543334151

Extended Methods:
Method #1

Plaintext: avonde
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
a v o n d e 
1 1 4 3 4 5 
1 5 3 3 1 1 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: avonde
Cipher: aoyvna

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Method #3

Plaintext: avonde
method variations:
aunsva unsvaa nsvaau
svaaun vaauns aaunsv

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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: avonde

all 720 cipher variations:
avonde avoned avodne avoden avoedn avoend avnode avnoed avndoe avndeo avnedo
avneod avdnoe avdneo avdone avdoen avdeon avdeno avendo avenod avedno avedon
aveodn aveond aovnde aovned aovdne aovden aovedn aovend aonvde aonved aondve
aondev aonedv aonevd aodnve aodnev aodvne aodven aodevn aodenv aoendv aoenvd
aoednv aoedvn aoevdn aoevnd anovde anoved anodve anodev anoedv anoevd anvode
anvoed anvdoe anvdeo anvedo anveod andvoe andveo andove andoev andeov andevo
anevdo anevod anedvo anedov aneodv aneovd adonve adonev adovne adoven adoevn
adoenv adnove adnoev adnvoe adnveo adnevo adneov advnoe advneo advone advoen
adveon adveno adenvo adenov adevno adevon adeovn adeonv aeondv aeonvd aeodnv
aeodvn aeovdn aeovnd aenodv aenovd aendov aendvo aenvdo aenvod aednov aednvo
aedonv aedovn aedvon aedvno aevndo aevnod aevdno aevdon aevodn aevond vaonde
vaoned vaodne vaoden vaoedn vaoend vanode vanoed vandoe vandeo vanedo vaneod
vadnoe vadneo vadone vadoen vadeon vadeno vaendo vaenod vaedno vaedon vaeodn
vaeond voande voaned voadne voaden voaedn voaend vonade vonaed vondae vondea
voneda vonead vodnae vodnea vodane vodaen vodean vodena voenda voenad voedna
voedan voeadn voeand vnoade vnoaed vnodae vnodea vnoeda vnoead vnaode vnaoed
vnadoe vnadeo vnaedo vnaeod vndaoe vndaeo vndoae vndoea vndeoa vndeao vneado
vneaod vnedao vnedoa vneoda vneoad vdonae vdonea vdoane vdoaen vdoean vdoena
vdnoae vdnoea vdnaoe vdnaeo vdneao vdneoa vdanoe vdaneo vdaone vdaoen vdaeon
vdaeno vdenao vdenoa vdeano vdeaon vdeoan vdeona veonda veonad veodna veodan
veoadn veoand venoda venoad vendoa vendao venado venaod vednoa vednao vedona
vedoan vedaon vedano veando veanod veadno veadon veaodn veaond ovande ovaned
ovadne ovaden ovaedn ovaend ovnade ovnaed ovndae ovndea ovneda ovnead ovdnae
ovdnea ovdane ovdaen ovdean ovdena ovenda ovenad ovedna ovedan oveadn oveand
oavnde oavned oavdne oavden oavedn oavend oanvde oanved oandve oandev oanedv
oanevd oadnve oadnev oadvne oadven oadevn oadenv oaendv oaenvd oaednv oaedvn
oaevdn oaevnd onavde onaved onadve onadev onaedv onaevd onvade onvaed onvdae
onvdea onveda onvead ondvae ondvea ondave ondaev ondeav ondeva onevda onevad
onedva onedav oneadv oneavd odanve odanev odavne odaven odaevn odaenv odnave
odnaev odnvae odnvea odneva odneav odvnae odvnea odvane odvaen odvean odvena
odenva odenav odevna odevan odeavn odeanv oeandv oeanvd oeadnv oeadvn oeavdn
oeavnd oenadv oenavd oendav oendva oenvda oenvad oednav oednva oedanv oedavn
oedvan oedvna oevnda oevnad oevdna oevdan oevadn oevand nvoade nvoaed nvodae
nvodea nvoeda nvoead nvaode nvaoed nvadoe nvadeo nvaedo nvaeod nvdaoe nvdaeo
nvdoae nvdoea nvdeoa nvdeao nveado nveaod nvedao nvedoa nveoda nveoad novade
novaed novdae novdea noveda novead noavde noaved noadve noadev noaedv noaevd
nodave nodaev nodvae nodvea nodeva nodeav noeadv noeavd noedav noedva noevda
noevad naovde naoved naodve naodev naoedv naoevd navode navoed navdoe navdeo
navedo naveod nadvoe nadveo nadove nadoev nadeov nadevo naevdo naevod naedvo
naedov naeodv naeovd ndoave ndoaev ndovae ndovea ndoeva ndoeav ndaove ndaoev
ndavoe ndaveo ndaevo ndaeov ndvaoe ndvaeo ndvoae ndvoea ndveoa ndveao ndeavo
ndeaov ndevao ndevoa ndeova ndeoav neoadv neoavd neodav neodva neovda neovad
neaodv neaovd neadov neadvo neavdo neavod nedaov nedavo nedoav nedova nedvoa
nedvao nevado nevaod nevdao nevdoa nevoda nevoad dvonae dvonea dvoane dvoaen
dvoean dvoena dvnoae dvnoea dvnaoe dvnaeo dvneao dvneoa dvanoe dvaneo dvaone
dvaoen dvaeon dvaeno dvenao dvenoa dveano dveaon dveoan dveona dovnae dovnea
dovane dovaen dovean dovena donvae donvea donave donaev doneav doneva doanve
doanev doavne doaven doaevn doaenv doenav doenva doeanv doeavn doevan doevna
dnovae dnovea dnoave dnoaev dnoeav dnoeva dnvoae dnvoea dnvaoe dnvaeo dnveao
dnveoa dnavoe dnaveo dnaove dnaoev dnaeov dnaevo dnevao dnevoa dneavo dneaov
dneoav dneova daonve daonev daovne daoven daoevn daoenv danove danoev danvoe
danveo danevo daneov davnoe davneo davone davoen daveon daveno daenvo daenov
daevno daevon daeovn daeonv deonav deonva deoanv deoavn deovan deovna denoav
denova denaov denavo denvao denvoa deanov deanvo deaonv deaovn deavon deavno
devnao devnoa devano devaon devoan devona evonda evonad evodna evodan evoadn
evoand evnoda evnoad evndoa evndao evnado evnaod evdnoa evdnao evdona evdoan
evdaon evdano evando evanod evadno evadon evaodn evaond eovnda eovnad eovdna
eovdan eovadn eovand eonvda eonvad eondva eondav eonadv eonavd eodnva eodnav
eodvna eodvan eodavn eodanv eoandv eoanvd eoadnv eoadvn eoavdn eoavnd enovda
enovad enodva enodav enoadv enoavd envoda envoad envdoa envdao envado envaod
endvoa endvao endova endoav endaov endavo enavdo enavod enadvo enadov enaodv
enaovd edonva edonav edovna edovan edoavn edoanv ednova ednoav ednvoa ednvao
ednavo ednaov edvnoa edvnao edvona edvoan edvaon edvano edanvo edanov edavno
edavon edaovn edaonv eaondv eaonvd eaodnv eaodvn eaovdn eaovnd eanodv eanovd
eandov eandvo eanvdo eanvod eadnov eadnvo eadonv eadovn eadvon eadvno eavndo
eavnod eavdno eavdon eavodn eavond

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History of cryptography
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