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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: jdavie
cipher variations:
kebwjf lfcxkg mgdylh nhezmi oifanj
pjgbok qkhcpl rlidqm smjern tnkfso
uolgtp vpmhuq wqnivr xrojws yspkxt
ztqlyu aurmzv bvsnaw cwtobx dxupcy
eyvqdz fzwrea gaxsfb hbytgc iczuhd

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: jdavie
Cipher: qwzerv

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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: jdavie

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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: jdavie
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: jdavie
Cipher: wqnivr

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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: jdavie
Cipher: 424111154251

Extended Methods:
Method #1

Plaintext: jdavie
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
j d a v i e 
4 4 1 1 4 5 
2 1 1 5 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: jdavie
Cipher: taybvb

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Method #3

Plaintext: jdavie
method variations:
raauwq aauwqr auwqra
uwqraa wqraau qraauw

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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: jdavie

all 720 cipher variations:
jdavie jdavei jdaive jdaiev jdaeiv jdaevi jdvaie jdvaei jdviae jdviea jdveia
jdveai jdivae jdivea jdiave jdiaev jdieav jdieva jdevia jdevai jdeiva jdeiav
jdeaiv jdeavi jadvie jadvei jadive jadiev jadeiv jadevi javdie javdei javide
javied javeid javedi jaivde jaived jaidve jaidev jaiedv jaievd jaevid jaevdi
jaeivd jaeidv jaediv jaedvi jvadie jvadei jvaide jvaied jvaeid jvaedi jvdaie
jvdaei jvdiae jvdiea jvdeia jvdeai jvidae jvidea jviade jviaed jviead jvieda
jvedia jvedai jveida jveiad jveaid jveadi jiavde jiaved jiadve jiadev jiaedv
jiaevd jivade jivaed jivdae jivdea jiveda jivead jidvae jidvea jidave jidaev
jideav jideva jievda jievad jiedva jiedav jieadv jieavd jeavid jeavdi jeaivd
jeaidv jeadiv jeadvi jevaid jevadi jeviad jevida jevdia jevdai jeivad jeivda
jeiavd jeiadv jeidav jeidva jedvia jedvai jediva jediav jedaiv jedavi djavie
djavei djaive djaiev djaeiv djaevi djvaie djvaei djviae djviea djveia djveai
djivae djivea djiave djiaev djieav djieva djevia djevai djeiva djeiav djeaiv
djeavi dajvie dajvei dajive dajiev dajeiv dajevi davjie davjei davije daviej
daveij daveji daivje daivej daijve daijev daiejv daievj daevij daevji daeivj
daeijv daejiv daejvi dvajie dvajei dvaije dvaiej dvaeij dvaeji dvjaie dvjaei
dvjiae dvjiea dvjeia dvjeai dvijae dvijea dviaje dviaej dvieaj dvieja dvejia
dvejai dveija dveiaj dveaij dveaji diavje diavej diajve diajev diaejv diaevj
divaje divaej divjae divjea diveja diveaj dijvae dijvea dijave dijaev dijeav
dijeva dievja dievaj diejva diejav dieajv dieavj deavij deavji deaivj deaijv
deajiv deajvi devaij devaji deviaj devija devjia devjai deivaj deivja deiavj
deiajv deijav deijva dejvia dejvai dejiva dejiav dejaiv dejavi adjvie adjvei
adjive adjiev adjeiv adjevi advjie advjei advije adviej adveij adveji adivje
adivej adijve adijev adiejv adievj adevij adevji adeivj adeijv adejiv adejvi
ajdvie ajdvei ajdive ajdiev ajdeiv ajdevi ajvdie ajvdei ajvide ajvied ajveid
ajvedi ajivde ajived ajidve ajidev ajiedv ajievd ajevid ajevdi ajeivd ajeidv
ajediv ajedvi avjdie avjdei avjide avjied avjeid avjedi avdjie avdjei avdije
avdiej avdeij avdeji avidje avidej avijde avijed aviejd aviedj avedij avedji
aveidj aveijd avejid avejdi aijvde aijved aijdve aijdev aijedv aijevd aivjde
aivjed aivdje aivdej aivedj aivejd aidvje aidvej aidjve aidjev aidejv aidevj
aievdj aievjd aiedvj aiedjv aiejdv aiejvd aejvid aejvdi aejivd aejidv aejdiv
aejdvi aevjid aevjdi aevijd aevidj aevdij aevdji aeivjd aeivdj aeijvd aeijdv
aeidjv aeidvj aedvij aedvji aedivj aedijv aedjiv aedjvi vdajie vdajei vdaije
vdaiej vdaeij vdaeji vdjaie vdjaei vdjiae vdjiea vdjeia vdjeai vdijae vdijea
vdiaje vdiaej vdieaj vdieja vdejia vdejai vdeija vdeiaj vdeaij vdeaji vadjie
vadjei vadije vadiej vadeij vadeji vajdie vajdei vajide vajied vajeid vajedi
vaijde vaijed vaidje vaidej vaiedj vaiejd vaejid vaejdi vaeijd vaeidj vaedij
vaedji vjadie vjadei vjaide vjaied vjaeid vjaedi vjdaie vjdaei vjdiae vjdiea
vjdeia vjdeai vjidae vjidea vjiade vjiaed vjiead vjieda vjedia vjedai vjeida
vjeiad vjeaid vjeadi viajde viajed viadje viadej viaedj viaejd vijade vijaed
vijdae vijdea vijeda vijead vidjae vidjea vidaje vidaej videaj videja viejda
viejad viedja viedaj vieadj vieajd veajid veajdi veaijd veaidj veadij veadji
vejaid vejadi vejiad vejida vejdia vejdai veijad veijda veiajd veiadj veidaj
veidja vedjia vedjai vedija vediaj vedaij vedaji idavje idavej idajve idajev
idaejv idaevj idvaje idvaej idvjae idvjea idveja idveaj idjvae idjvea idjave
idjaev idjeav idjeva idevja idevaj idejva idejav ideajv ideavj iadvje iadvej
iadjve iadjev iadejv iadevj iavdje iavdej iavjde iavjed iavejd iavedj iajvde
iajved iajdve iajdev iajedv iajevd iaevjd iaevdj iaejvd iaejdv iaedjv iaedvj
ivadje ivadej ivajde ivajed ivaejd ivaedj ivdaje ivdaej ivdjae ivdjea ivdeja
ivdeaj ivjdae ivjdea ivjade ivjaed ivjead ivjeda ivedja ivedaj ivejda ivejad
iveajd iveadj ijavde ijaved ijadve ijadev ijaedv ijaevd ijvade ijvaed ijvdae
ijvdea ijveda ijvead ijdvae ijdvea ijdave ijdaev ijdeav ijdeva ijevda ijevad
ijedva ijedav ijeadv ijeavd ieavjd ieavdj ieajvd ieajdv ieadjv ieadvj ievajd
ievadj ievjad ievjda ievdja ievdaj iejvad iejvda iejavd iejadv iejdav iejdva
iedvja iedvaj iedjva iedjav iedajv iedavj edavij edavji edaivj edaijv edajiv
edajvi edvaij edvaji edviaj edvija edvjia edvjai edivaj edivja ediavj ediajv
edijav edijva edjvia edjvai edjiva edjiav edjaiv edjavi eadvij eadvji eadivj
eadijv eadjiv eadjvi eavdij eavdji eavidj eavijd eavjid eavjdi eaivdj eaivjd
eaidvj eaidjv eaijdv eaijvd eajvid eajvdi eajivd eajidv eajdiv eajdvi evadij
evadji evaidj evaijd evajid evajdi evdaij evdaji evdiaj evdija evdjia evdjai
evidaj evidja eviadj eviajd evijad evijda evjdia evjdai evjida evjiad evjaid
evjadi eiavdj eiavjd eiadvj eiadjv eiajdv eiajvd eivadj eivajd eivdaj eivdja
eivjda eivjad eidvaj eidvja eidavj eidajv eidjav eidjva eijvda eijvad eijdva
eijdav eijadv eijavd ejavid ejavdi ejaivd ejaidv ejadiv ejadvi ejvaid ejvadi
ejviad ejvida ejvdia ejvdai ejivad ejivda ejiavd ejiadv ejidav ejidva ejdvia
ejdvai ejdiva ejdiav ejdaiv ejdavi

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History of cryptography
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