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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: alfier
cipher variations:
bmgjfs cnhkgt doilhu epjmiv fqknjw
grlokx hsmply itnqmz juorna kvpsob
lwqtpc mxruqd nysvre oztwsf pauxtg
qbvyuh rcwzvi sdxawj teybxk ufzcyl
vgadzm whbean xicfbo yjdgcp zkehdq

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: alfier
Cipher: zourvi

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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: alfier

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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: alfier
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: alfier
Cipher: nysvre

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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: alfier
Cipher: 111312425124

Extended Methods:
Method #1

Plaintext: alfier
method variations:

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

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Method #3

Plaintext: alfier
method variations:
acrwfd crwfda rwfdac
wfdacr fdacrw dacrwf

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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: alfier

all 720 cipher variations:
alfier alfire alfeir alferi alfrei alfrie alifer alifre aliefr alierf aliref
alirfe aleifr aleirf alefir alefri alerfi alerif alrief alrife alreif alrefi
alrfei alrfie aflier aflire afleir afleri aflrei aflrie afiler afilre afielr
afierl afirel afirle afeilr afeirl afelir afelri aferli aferil afriel afrile
afreil afreli afrlei afrlie aifler aiflre aifelr aiferl aifrel aifrle ailfer
ailfre ailefr ailerf ailref ailrfe aielfr aielrf aieflr aiefrl aierfl aierlf
airlef airlfe airelf airefl airfel airfle aefilr aefirl aeflir aeflri aefrli
aefril aeiflr aeifrl aeilfr aeilrf aeirlf aeirfl aelifr aelirf aelfir aelfri
aelrfi aelrif aerilf aerifl aerlif aerlfi aerfli aerfil arfiel arfile arfeil
arfeli arflei arflie arifel arifle ariefl arielf arilef arilfe areifl areilf
arefil arefli arelfi arelif arlief arlife arleif arlefi arlfei arlfie lafier
lafire lafeir laferi lafrei lafrie laifer laifre laiefr laierf lairef lairfe
laeifr laeirf laefir laefri laerfi laerif larief larife lareif larefi larfei
larfie lfaier lfaire lfaeir lfaeri lfarei lfarie lfiaer lfiare lfiear lfiera
lfirea lfirae lfeiar lfeira lfeair lfeari lferai lferia lfriea lfriae lfreia
lfreai lfraei lfraie lifaer lifare lifear lifera lifrea lifrae liafer liafre
liaefr liaerf liaref liarfe lieafr liearf liefar liefra lierfa lieraf liraef
lirafe lireaf lirefa lirfea lirfae lefiar lefira lefair lefari lefrai lefria
leifar leifra leiafr leiarf leiraf leirfa leaifr leairf leafir leafri learfi
learif leriaf lerifa leraif lerafi lerfai lerfia lrfiea lrfiae lrfeia lrfeai
lrfaei lrfaie lrifea lrifae lriefa lrieaf lriaef lriafe lreifa lreiaf lrefia
lrefai lreafi lreaif lraief lraife lraeif lraefi lrafei lrafie flaier flaire
flaeir flaeri flarei flarie fliaer fliare fliear fliera flirea flirae fleiar
fleira fleair fleari flerai fleria flriea flriae flreia flreai flraei flraie
falier falire faleir faleri falrei falrie failer failre faielr faierl fairel
fairle faeilr faeirl faelir faelri faerli faeril fariel farile fareil fareli
farlei farlie fialer fialre fiaelr fiaerl fiarel fiarle filaer filare filear
filera filrea filrae fielar fielra fiealr fiearl fieral fierla firlea firlae
firela fireal firael firale feailr feairl fealir fealri fearli fearil feialr
feiarl feilar feilra feirla feiral feliar felira felair felari felrai felria
ferila ferial ferlia ferlai ferali ferail fraiel fraile fraeil fraeli fralei
fralie friael friale frieal friela frilea frilae freial freila freail freali
frelai frelia frliea frliae frleia frleai frlaei frlaie ilfaer ilfare ilfear
ilfera ilfrea ilfrae ilafer ilafre ilaefr ilaerf ilaref ilarfe ileafr ilearf
ilefar ilefra ilerfa ileraf ilraef ilrafe ilreaf ilrefa ilrfea ilrfae iflaer
iflare iflear iflera iflrea iflrae ifaler ifalre ifaelr ifaerl ifarel ifarle
ifealr ifearl ifelar ifelra iferla iferal ifrael ifrale ifreal ifrela ifrlea
ifrlae iafler iaflre iafelr iaferl iafrel iafrle ialfer ialfre ialefr ialerf
ialref ialrfe iaelfr iaelrf iaeflr iaefrl iaerfl iaerlf iarlef iarlfe iarelf
iarefl iarfel iarfle iefalr iefarl ieflar ieflra iefrla iefral ieaflr ieafrl
iealfr iealrf iearlf iearfl ielafr ielarf ielfar ielfra ielrfa ielraf ieralf
ierafl ierlaf ierlfa ierfla ierfal irfael irfale irfeal irfela irflea irflae
irafel irafle iraefl iraelf iralef iralfe ireafl irealf irefal irefla irelfa
irelaf irlaef irlafe irleaf irlefa irlfea irlfae elfiar elfira elfair elfari
elfrai elfria elifar elifra eliafr eliarf eliraf elirfa elaifr elairf elafir
elafri elarfi elarif elriaf elrifa elraif elrafi elrfai elrfia efliar eflira
eflair eflari eflrai eflria efilar efilra efialr efiarl efiral efirla efailr
efairl efalir efalri efarli efaril efrial efrila efrail efrali efrlai efrlia
eiflar eiflra eifalr eifarl eifral eifrla eilfar eilfra eilafr eilarf eilraf
eilrfa eialfr eialrf eiaflr eiafrl eiarfl eiarlf eirlaf eirlfa eiralf eirafl
eirfal eirfla eafilr eafirl eaflir eaflri eafrli eafril eaiflr eaifrl eailfr
eailrf eairlf eairfl ealifr ealirf ealfir ealfri ealrfi ealrif earilf earifl
earlif earlfi earfli earfil erfial erfila erfail erfali erflai erflia erifal
erifla eriafl erialf erilaf erilfa eraifl erailf erafil erafli eralfi eralif
erliaf erlifa erlaif erlafi erlfai erlfia rlfiea rlfiae rlfeia rlfeai rlfaei
rlfaie rlifea rlifae rliefa rlieaf rliaef rliafe rleifa rleiaf rlefia rlefai
rleafi rleaif rlaief rlaife rlaeif rlaefi rlafei rlafie rfliea rfliae rfleia
rfleai rflaei rflaie rfilea rfilae rfiela rfieal rfiael rfiale rfeila rfeial
rfelia rfelai rfeali rfeail rfaiel rfaile rfaeil rfaeli rfalei rfalie riflea
riflae rifela rifeal rifael rifale rilfea rilfae rilefa rileaf rilaef rilafe
rielfa rielaf riefla riefal rieafl riealf rialef rialfe riaelf riaefl riafel
riafle refila refial reflia reflai refali refail reifla reifal reilfa reilaf
reialf reiafl relifa reliaf relfia relfai relafi relaif reailf reaifl realif
realfi reafli reafil rafiel rafile rafeil rafeli raflei raflie raifel raifle
raiefl raielf railef railfe raeifl raeilf raefil raefli raelfi raelif ralief
ralife raleif ralefi ralfei ralfie

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History of cryptography
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