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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: houlik
cipher variations:
ipvmjl jqwnkm krxoln lsypmo mtzqnp
nuaroq ovbspr pwctqs qxdurt ryevsu
szfwtv tagxuw ubhyvx vcizwy wdjaxz
xekbya yflczb zgmdac ahnebd biofce
cjpgdf dkqheg elrifh fmsjgi gntkhj

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: houlik
Cipher: slforp

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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: houlik

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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: houlik
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: houlik
Cipher: ubhyvx

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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: houlik
Cipher: 324354134252

Extended Methods:
Method #1

Plaintext: houlik
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
h o u l i k 
3 4 5 1 4 5 
2 3 4 3 2 2 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: houlik
Cipher: seymog

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Method #3

Plaintext: houlik
method variations:
rxdswm xdswmr dswmrx
swmrxd wmrxds mrxdsw

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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: houlik

all 720 cipher variations:
houlik houlki houilk houikl houkil houkli holuik holuki holiuk holiku holkiu
holkui hoiluk hoilku hoiulk hoiukl hoikul hoiklu hokliu hoklui hokilu hokiul
hokuil hokuli huolik huolki huoilk huoikl huokil huokli huloik huloki huliok
huliko hulkio hulkoi huilok huilko huiolk huiokl huikol huiklo huklio hukloi
hukilo hukiol hukoil hukoli hluoik hluoki hluiok hluiko hlukio hlukoi hlouik
hlouki hloiuk hloiku hlokiu hlokui hliouk hlioku hliuok hliuko hlikuo hlikou
hlkoiu hlkoui hlkiou hlkiuo hlkuio hlkuoi hiulok hiulko hiuolk hiuokl hiukol
hiuklo hiluok hiluko hilouk hiloku hilkou hilkuo hioluk hiolku hioulk hioukl
hiokul hioklu hiklou hikluo hikolu hikoul hikuol hikulo hkulio hkuloi hkuilo
hkuiol hkuoil hkuoli hkluio hkluoi hkliuo hkliou hkloiu hkloui hkiluo hkilou
hkiulo hkiuol hkioul hkiolu hkoliu hkolui hkoilu hkoiul hkouil hkouli ohulik
ohulki ohuilk ohuikl ohukil ohukli ohluik ohluki ohliuk ohliku ohlkiu ohlkui
ohiluk ohilku ohiulk ohiukl ohikul ohiklu ohkliu ohklui ohkilu ohkiul ohkuil
ohkuli ouhlik ouhlki ouhilk ouhikl ouhkil ouhkli oulhik oulhki oulihk oulikh
oulkih oulkhi ouilhk ouilkh ouihlk ouihkl ouikhl ouiklh ouklih ouklhi oukilh
oukihl oukhil oukhli oluhik oluhki oluihk oluikh olukih olukhi olhuik olhuki
olhiuk olhiku olhkiu olhkui olihuk olihku oliuhk oliukh olikuh olikhu olkhiu
olkhui olkihu olkiuh olkuih olkuhi oiulhk oiulkh oiuhlk oiuhkl oiukhl oiuklh
oiluhk oilukh oilhuk oilhku oilkhu oilkuh oihluk oihlku oihulk oihukl oihkul
oihklu oiklhu oikluh oikhlu oikhul oikuhl oikulh okulih okulhi okuilh okuihl
okuhil okuhli okluih okluhi okliuh oklihu oklhiu oklhui okiluh okilhu okiulh
okiuhl okihul okihlu okhliu okhlui okhilu okhiul okhuil okhuli uohlik uohlki
uohilk uohikl uohkil uohkli uolhik uolhki uolihk uolikh uolkih uolkhi uoilhk
uoilkh uoihlk uoihkl uoikhl uoiklh uoklih uoklhi uokilh uokihl uokhil uokhli
uholik uholki uhoilk uhoikl uhokil uhokli uhloik uhloki uhliok uhliko uhlkio
uhlkoi uhilok uhilko uhiolk uhiokl uhikol uhiklo uhklio uhkloi uhkilo uhkiol
uhkoil uhkoli ulhoik ulhoki ulhiok ulhiko ulhkio ulhkoi ulohik ulohki uloihk
uloikh ulokih ulokhi uliohk uliokh ulihok ulihko ulikho ulikoh ulkoih ulkohi
ulkioh ulkiho ulkhio ulkhoi uihlok uihlko uiholk uihokl uihkol uihklo uilhok
uilhko uilohk uilokh uilkoh uilkho uiolhk uiolkh uiohlk uiohkl uiokhl uioklh
uikloh uiklho uikolh uikohl uikhol uikhlo ukhlio ukhloi ukhilo ukhiol ukhoil
ukholi uklhio uklhoi ukliho uklioh ukloih uklohi ukilho ukiloh ukihlo ukihol
ukiohl ukiolh ukolih ukolhi ukoilh ukoihl ukohil ukohli louhik louhki louihk
louikh loukih loukhi lohuik lohuki lohiuk lohiku lohkiu lohkui loihuk loihku
loiuhk loiukh loikuh loikhu lokhiu lokhui lokihu lokiuh lokuih lokuhi luohik
luohki luoihk luoikh luokih luokhi luhoik luhoki luhiok luhiko luhkio luhkoi
luihok luihko luiohk luiokh luikoh luikho lukhio lukhoi lukiho lukioh lukoih
lukohi lhuoik lhuoki lhuiok lhuiko lhukio lhukoi lhouik lhouki lhoiuk lhoiku
lhokiu lhokui lhiouk lhioku lhiuok lhiuko lhikuo lhikou lhkoiu lhkoui lhkiou
lhkiuo lhkuio lhkuoi liuhok liuhko liuohk liuokh liukoh liukho lihuok lihuko
lihouk lihoku lihkou lihkuo liohuk liohku liouhk lioukh liokuh liokhu likhou
likhuo likohu likouh likuoh likuho lkuhio lkuhoi lkuiho lkuioh lkuoih lkuohi
lkhuio lkhuoi lkhiuo lkhiou lkhoiu lkhoui lkihuo lkihou lkiuho lkiuoh lkiouh
lkiohu lkohiu lkohui lkoihu lkoiuh lkouih lkouhi ioulhk ioulkh iouhlk iouhkl
ioukhl iouklh ioluhk iolukh iolhuk iolhku iolkhu iolkuh iohluk iohlku iohulk
iohukl iohkul iohklu ioklhu iokluh iokhlu iokhul iokuhl iokulh iuolhk iuolkh
iuohlk iuohkl iuokhl iuoklh iulohk iulokh iulhok iulhko iulkho iulkoh iuhlok
iuhlko iuholk iuhokl iuhkol iuhklo iuklho iukloh iukhlo iukhol iukohl iukolh
iluohk iluokh iluhok iluhko ilukho ilukoh ilouhk iloukh ilohuk ilohku ilokhu
ilokuh ilhouk ilhoku ilhuok ilhuko ilhkuo ilhkou ilkohu ilkouh ilkhou ilkhuo
ilkuho ilkuoh ihulok ihulko ihuolk ihuokl ihukol ihuklo ihluok ihluko ihlouk
ihloku ihlkou ihlkuo iholuk iholku ihoulk ihoukl ihokul ihoklu ihklou ihkluo
ihkolu ihkoul ihkuol ihkulo ikulho ikuloh ikuhlo ikuhol ikuohl ikuolh ikluho
ikluoh iklhuo iklhou iklohu iklouh ikhluo ikhlou ikhulo ikhuol ikhoul ikholu
ikolhu ikoluh ikohlu ikohul ikouhl ikoulh koulih koulhi kouilh kouihl kouhil
kouhli koluih koluhi koliuh kolihu kolhiu kolhui koiluh koilhu koiulh koiuhl
koihul koihlu kohliu kohlui kohilu kohiul kohuil kohuli kuolih kuolhi kuoilh
kuoihl kuohil kuohli kuloih kulohi kulioh kuliho kulhio kulhoi kuiloh kuilho
kuiolh kuiohl kuihol kuihlo kuhlio kuhloi kuhilo kuhiol kuhoil kuholi kluoih
kluohi kluioh kluiho kluhio kluhoi klouih klouhi kloiuh kloihu klohiu klohui
kliouh kliohu kliuoh kliuho klihuo klihou klhoiu klhoui klhiou klhiuo klhuio
klhuoi kiuloh kiulho kiuolh kiuohl kiuhol kiuhlo kiluoh kiluho kilouh kilohu
kilhou kilhuo kioluh kiolhu kioulh kiouhl kiohul kiohlu kihlou kihluo kiholu
kihoul kihuol kihulo khulio khuloi khuilo khuiol khuoil khuoli khluio khluoi
khliuo khliou khloiu khloui khiluo khilou khiulo khiuol khioul khiolu kholiu
kholui khoilu khoiul khouil khouli

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History of cryptography
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