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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: djerib
cipher variations:
ekfsjc flgtkd gmhule hnivmf iojwng
jpkxoh kqlypi lrmzqj msnark ntobsl
oupctm pvqdun qwrevo rxsfwp sytgxq
tzuhyr uavizs vbwjat wcxkbu xdylcv
yezmdw zfanex agbofy bhcpgz cidqha

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: djerib
Cipher: wqviry

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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: djerib

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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: djerib
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: djerib
Cipher: qwrevo

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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: djerib
Cipher: 414251244221

Extended Methods:
Method #1

Plaintext: djerib
method variations:

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

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Method #3

Plaintext: djerib
method variations:
qwftgq wftgqq ftgqqw
tgqqwf gqqwft qqwftg

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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: djerib

all 720 cipher variations:
djerib djerbi djeirb djeibr djebir djebri djreib djrebi djrieb djribe djrbie
djrbei djireb djirbe djierb djiebr djiber djibre djbrie djbrei djbire djbier
djbeir djberi dejrib dejrbi dejirb dejibr dejbir dejbri derjib derjbi derijb
deribj derbij derbji deirjb deirbj deijrb deijbr deibjr deibrj debrij debrji
debirj debijr debjir debjri drejib drejbi dreijb dreibj drebij drebji drjeib
drjebi drjieb drjibe drjbie drjbei drijeb drijbe driejb driebj dribej dribje
drbjie drbjei drbije drbiej drbeij drbeji dierjb dierbj diejrb diejbr diebjr
diebrj direjb direbj dirjeb dirjbe dirbje dirbej dijreb dijrbe dijerb dijebr
dijber dijbre dibrje dibrej dibjre dibjer dibejr diberj dberij dberji dbeirj
dbeijr dbejir dbejri dbreij dbreji dbriej dbrije dbrjie dbrjei dbirej dbirje
dbierj dbiejr dbijer dbijre dbjrie dbjrei dbjire dbjier dbjeir dbjeri jderib
jderbi jdeirb jdeibr jdebir jdebri jdreib jdrebi jdrieb jdribe jdrbie jdrbei
jdireb jdirbe jdierb jdiebr jdiber jdibre jdbrie jdbrei jdbire jdbier jdbeir
jdberi jedrib jedrbi jedirb jedibr jedbir jedbri jerdib jerdbi jeridb jeribd
jerbid jerbdi jeirdb jeirbd jeidrb jeidbr jeibdr jeibrd jebrid jebrdi jebird
jebidr jebdir jebdri jredib jredbi jreidb jreibd jrebid jrebdi jrdeib jrdebi
jrdieb jrdibe jrdbie jrdbei jrideb jridbe jriedb jriebd jribed jribde jrbdie
jrbdei jrbide jrbied jrbeid jrbedi jierdb jierbd jiedrb jiedbr jiebdr jiebrd
jiredb jirebd jirdeb jirdbe jirbde jirbed jidreb jidrbe jiderb jidebr jidber
jidbre jibrde jibred jibdre jibder jibedr jiberd jberid jberdi jbeird jbeidr
jbedir jbedri jbreid jbredi jbried jbride jbrdie jbrdei jbired jbirde jbierd
jbiedr jbider jbidre jbdrie jbdrei jbdire jbdier jbdeir jbderi ejdrib ejdrbi
ejdirb ejdibr ejdbir ejdbri ejrdib ejrdbi ejridb ejribd ejrbid ejrbdi ejirdb
ejirbd ejidrb ejidbr ejibdr ejibrd ejbrid ejbrdi ejbird ejbidr ejbdir ejbdri
edjrib edjrbi edjirb edjibr edjbir edjbri edrjib edrjbi edrijb edribj edrbij
edrbji edirjb edirbj edijrb edijbr edibjr edibrj edbrij edbrji edbirj edbijr
edbjir edbjri erdjib erdjbi erdijb erdibj erdbij erdbji erjdib erjdbi erjidb
erjibd erjbid erjbdi erijdb erijbd eridjb eridbj eribdj eribjd erbjid erbjdi
erbijd erbidj erbdij erbdji eidrjb eidrbj eidjrb eidjbr eidbjr eidbrj eirdjb
eirdbj eirjdb eirjbd eirbjd eirbdj eijrdb eijrbd eijdrb eijdbr eijbdr eijbrd
eibrjd eibrdj eibjrd eibjdr eibdjr eibdrj ebdrij ebdrji ebdirj ebdijr ebdjir
ebdjri ebrdij ebrdji ebridj ebrijd ebrjid ebrjdi ebirdj ebirjd ebidrj ebidjr
ebijdr ebijrd ebjrid ebjrdi ebjird ebjidr ebjdir ebjdri rjedib rjedbi rjeidb
rjeibd rjebid rjebdi rjdeib rjdebi rjdieb rjdibe rjdbie rjdbei rjideb rjidbe
rjiedb rjiebd rjibed rjibde rjbdie rjbdei rjbide rjbied rjbeid rjbedi rejdib
rejdbi rejidb rejibd rejbid rejbdi redjib redjbi redijb redibj redbij redbji
reidjb reidbj reijdb reijbd reibjd reibdj rebdij rebdji rebidj rebijd rebjid
rebjdi rdejib rdejbi rdeijb rdeibj rdebij rdebji rdjeib rdjebi rdjieb rdjibe
rdjbie rdjbei rdijeb rdijbe rdiejb rdiebj rdibej rdibje rdbjie rdbjei rdbije
rdbiej rdbeij rdbeji riedjb riedbj riejdb riejbd riebjd riebdj ridejb ridebj
ridjeb ridjbe ridbje ridbej rijdeb rijdbe rijedb rijebd rijbed rijbde ribdje
ribdej ribjde ribjed ribejd ribedj rbedij rbedji rbeidj rbeijd rbejid rbejdi
rbdeij rbdeji rbdiej rbdije rbdjie rbdjei rbidej rbidje rbiedj rbiejd rbijed
rbijde rbjdie rbjdei rbjide rbjied rbjeid rbjedi ijerdb ijerbd ijedrb ijedbr
ijebdr ijebrd ijredb ijrebd ijrdeb ijrdbe ijrbde ijrbed ijdreb ijdrbe ijderb
ijdebr ijdber ijdbre ijbrde ijbred ijbdre ijbder ijbedr ijberd iejrdb iejrbd
iejdrb iejdbr iejbdr iejbrd ierjdb ierjbd ierdjb ierdbj ierbdj ierbjd iedrjb
iedrbj iedjrb iedjbr iedbjr iedbrj iebrdj iebrjd iebdrj iebdjr iebjdr iebjrd
irejdb irejbd iredjb iredbj irebdj irebjd irjedb irjebd irjdeb irjdbe irjbde
irjbed irdjeb irdjbe irdejb irdebj irdbej irdbje irbjde irbjed irbdje irbdej
irbedj irbejd iderjb iderbj idejrb idejbr idebjr idebrj idrejb idrebj idrjeb
idrjbe idrbje idrbej idjreb idjrbe idjerb idjebr idjber idjbre idbrje idbrej
idbjre idbjer idbejr idberj iberdj iberjd ibedrj ibedjr ibejdr ibejrd ibredj
ibrejd ibrdej ibrdje ibrjde ibrjed ibdrej ibdrje ibderj ibdejr ibdjer ibdjre
ibjrde ibjred ibjdre ibjder ibjedr ibjerd bjerid bjerdi bjeird bjeidr bjedir
bjedri bjreid bjredi bjried bjride bjrdie bjrdei bjired bjirde bjierd bjiedr
bjider bjidre bjdrie bjdrei bjdire bjdier bjdeir bjderi bejrid bejrdi bejird
bejidr bejdir bejdri berjid berjdi berijd beridj berdij berdji beirjd beirdj
beijrd beijdr beidjr beidrj bedrij bedrji bedirj bedijr bedjir bedjri brejid
brejdi breijd breidj bredij bredji brjeid brjedi brjied brjide brjdie brjdei
brijed brijde briejd briedj bridej bridje brdjie brdjei brdije brdiej brdeij
brdeji bierjd bierdj biejrd biejdr biedjr biedrj birejd biredj birjed birjde
birdje birdej bijred bijrde bijerd bijedr bijder bijdre bidrje bidrej bidjre
bidjer bidejr biderj bderij bderji bdeirj bdeijr bdejir bdejri bdreij bdreji
bdriej bdrije bdrjie bdrjei bdirej bdirje bdierj bdiejr bdijer bdijre bdjrie
bdjrei bdjire bdjier bdjeir bdjeri

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History of cryptography
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