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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: galeid
cipher variations:
hbmfje icngkf jdohlg kepimh lfqjni
mgrkoj nhslpk oitmql pjunrm qkvosn
rlwpto smxqup tnyrvq uozswr vpatxs
wqbuyt xrcvzu ysdwav ztexbw aufycx
bvgzdy cwhaez dxibfa eyjcgb fzkdhc

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: galeid
Cipher: tzovrw

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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: galeid

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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: galeid
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: galeid
Cipher: tnyrvq

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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: galeid
Cipher: 221113514241

Extended Methods:
Method #1

Plaintext: galeid
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
g a l e i d 
2 1 1 5 4 4 
2 1 3 1 2 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: galeid
Cipher: bvtbcb

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Method #3

Plaintext: galeid
method variations:
baxqrf axqrfb xqrfba
qrfbax rfbaxq fbaxqr

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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: galeid

all 720 cipher variations:
galeid galedi galied galide galdie galdei gaelid gaeldi gaeild gaeidl gaedil
gaedli gaield gaiedl gailed gailde gaidle gaidel gadeil gadeli gadiel gadile
gadlie gadlei glaeid glaedi glaied glaide gladie gladei gleaid gleadi gleiad
gleida gledia gledai gliead glieda gliaed gliade glidae glidea gldeia gldeai
gldiea gldiae gldaie gldaei gelaid geladi geliad gelida geldia geldai gealid
gealdi geaild geaidl geadil geadli geiald geiadl geilad geilda geidla geidal
gedail gedali gedial gedila gedlia gedlai gilead gileda gilaed gilade gildae
gildea gielad gielda gieald gieadl giedal giedla giaeld giaedl gialed gialde
giadle giadel gideal gidela gidael gidale gidlae gidlea gdleia gdleai gdliea
gdliae gdlaie gdlaei gdelia gdelai gdeila gdeial gdeail gdeali gdiela gdieal
gdilea gdilae gdiale gdiael gdaeil gdaeli gdaiel gdaile gdalie gdalei agleid
agledi aglied aglide agldie agldei agelid ageldi ageild ageidl agedil agedli
agield agiedl agiled agilde agidle agidel agdeil agdeli agdiel agdile agdlie
agdlei algeid algedi algied algide algdie algdei alegid alegdi aleigd aleidg
aledig aledgi aliegd aliedg aliged aligde alidge alideg aldeig aldegi aldieg
aldige aldgie aldgei aelgid aelgdi aeligd aelidg aeldig aeldgi aeglid aegldi
aegild aegidl aegdil aegdli aeigld aeigdl aeilgd aeildg aeidlg aeidgl aedgil
aedgli aedigl aedilg aedlig aedlgi ailegd ailedg ailged ailgde aildge aildeg
aielgd aieldg aiegld aiegdl aiedgl aiedlg aigeld aigedl aigled aiglde aigdle
aigdel aidegl aidelg aidgel aidgle aidlge aidleg adleig adlegi adlieg adlige
adlgie adlgei adelig adelgi adeilg adeigl adegil adegli adielg adiegl adileg
adilge adigle adigel adgeil adgeli adgiel adgile adglie adglei lageid lagedi
lagied lagide lagdie lagdei laegid laegdi laeigd laeidg laedig laedgi laiegd
laiedg laiged laigde laidge laideg ladeig ladegi ladieg ladige ladgie ladgei
lgaeid lgaedi lgaied lgaide lgadie lgadei lgeaid lgeadi lgeiad lgeida lgedia
lgedai lgiead lgieda lgiaed lgiade lgidae lgidea lgdeia lgdeai lgdiea lgdiae
lgdaie lgdaei legaid legadi legiad legida legdia legdai leagid leagdi leaigd
leaidg leadig leadgi leiagd leiadg leigad leigda leidga leidag ledaig ledagi
lediag lediga ledgia ledgai ligead ligeda ligaed ligade ligdae ligdea liegad
liegda lieagd lieadg liedag liedga liaegd liaedg liaged liagde liadge liadeg
lideag lidega lidaeg lidage lidgae lidgea ldgeia ldgeai ldgiea ldgiae ldgaie
ldgaei ldegia ldegai ldeiga ldeiag ldeaig ldeagi ldiega ldieag ldigea ldigae
ldiage ldiaeg ldaeig ldaegi ldaieg ldaige ldagie ldagei ealgid ealgdi ealigd
ealidg ealdig ealdgi eaglid eagldi eagild eagidl eagdil eagdli eaigld eaigdl
eailgd eaildg eaidlg eaidgl eadgil eadgli eadigl eadilg eadlig eadlgi elagid
elagdi elaigd elaidg eladig eladgi elgaid elgadi elgiad elgida elgdia elgdai
eligad eligda eliagd eliadg elidag elidga eldgia eldgai eldiga eldiag eldaig
eldagi eglaid egladi egliad eglida egldia egldai egalid egaldi egaild egaidl
egadil egadli egiald egiadl egilad egilda egidla egidal egdail egdali egdial
egdila egdlia egdlai eilgad eilgda eilagd eiladg eildag eildga eiglad eiglda
eigald eigadl eigdal eigdla eiagld eiagdl eialgd eialdg eiadlg eiadgl eidgal
eidgla eidagl eidalg eidlag eidlga edlgia edlgai edliga edliag edlaig edlagi
edglia edglai edgila edgial edgail edgali edigla edigal edilga edilag edialg
ediagl edagil edagli edaigl edailg edalig edalgi ialegd ialedg ialged ialgde
ialdge ialdeg iaelgd iaeldg iaegld iaegdl iaedgl iaedlg iageld iagedl iagled
iaglde iagdle iagdel iadegl iadelg iadgel iadgle iadlge iadleg ilaegd ilaedg
ilaged ilagde iladge iladeg ileagd ileadg ilegad ilegda iledga iledag ilgead
ilgeda ilgaed ilgade ilgdae ilgdea ildega ildeag ildgea ildgae ildage ildaeg
ielagd ieladg ielgad ielgda ieldga ieldag iealgd iealdg ieagld ieagdl ieadgl
ieadlg iegald iegadl ieglad ieglda iegdla iegdal iedagl iedalg iedgal iedgla
iedlga iedlag iglead igleda iglaed iglade igldae igldea igelad igelda igeald
igeadl igedal igedla igaeld igaedl igaled igalde igadle igadel igdeal igdela
igdael igdale igdlae igdlea idlega idleag idlgea idlgae idlage idlaeg idelga
idelag idegla idegal ideagl idealg idgela idgeal idglea idglae idgale idgael
idaegl idaelg idagel idagle idalge idaleg daleig dalegi dalieg dalige dalgie
dalgei daelig daelgi daeilg daeigl daegil daegli daielg daiegl daileg dailge
daigle daigel dageil dageli dagiel dagile daglie daglei dlaeig dlaegi dlaieg
dlaige dlagie dlagei dleaig dleagi dleiag dleiga dlegia dlegai dlieag dliega
dliaeg dliage dligae dligea dlgeia dlgeai dlgiea dlgiae dlgaie dlgaei delaig
delagi deliag deliga delgia delgai dealig dealgi deailg deaigl deagil deagli
deialg deiagl deilag deilga deigla deigal degail degali degial degila deglia
deglai dileag dilega dilaeg dilage dilgae dilgea dielag dielga diealg dieagl
diegal diegla diaelg diaegl dialeg dialge diagle diagel digeal digela digael
digale diglae diglea dgleia dgleai dgliea dgliae dglaie dglaei dgelia dgelai
dgeila dgeial dgeail dgeali dgiela dgieal dgilea dgilae dgiale dgiael dgaeil
dgaeli dgaiel dgaile dgalie dgalei

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History of cryptography
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