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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: relink
cipher variations:
sfmjol tgnkpm uholqn vipmro wjqnsp
xkrotq ylspur zmtqvs anurwt bovsxu
cpwtyv dqxuzw eryvax fszwby gtaxcz
hubyda ivczeb jwdafc kxebgd lyfche
mzgdif nahejg obifkh pcjgli qdkhmj

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: relink
Cipher: ivormp

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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: relink

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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: relink
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: relink
Cipher: eryvax

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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: relink
Cipher: 245113423352

Extended Methods:
Method #1

Plaintext: relink
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
r e l i n k 
2 5 1 4 3 5 
4 1 3 2 3 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: relink
Cipher: wqxdhh

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Method #3

Plaintext: relink
method variations:
yasmxg asmxgy smxgya
mxgyas xgyasm gyasmx

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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: relink

all 720 cipher variations:
relink relikn relnik relnki relkni relkin reilnk reilkn reinlk reinkl reiknl
reikln renilk renikl renlik renlki renkli renkil rekinl rekiln reknil reknli
reklni reklin rleink rleikn rlenik rlenki rlekni rlekin rlienk rliekn rlinek
rlinke rlikne rliken rlniek rlnike rlneik rlneki rlnkei rlnkie rlkine rlkien
rlknie rlknei rlkeni rlkein rilenk rilekn rilnek rilnke rilkne rilken rielnk
rielkn rienlk rienkl rieknl riekln rinelk rinekl rinlek rinlke rinkle rinkel
rikenl rikeln riknel riknle riklne riklen rnliek rnlike rnleik rnleki rnlkei
rnlkie rnilek rnilke rnielk rniekl rnikel rnikle rneilk rneikl rnelik rnelki
rnekli rnekil rnkiel rnkile rnkeil rnkeli rnklei rnklie rkline rklien rklnie
rklnei rkleni rklein rkilne rkilen rkinle rkinel rkienl rkieln rknile rkniel
rknlie rknlei rkneli rkneil rkeinl rkeiln rkenil rkenli rkelni rkelin erlink
erlikn erlnik erlnki erlkni erlkin erilnk erilkn erinlk erinkl eriknl erikln
ernilk ernikl ernlik ernlki ernkli ernkil erkinl erkiln erknil erknli erklni
erklin elrink elrikn elrnik elrnki elrkni elrkin elirnk elirkn elinrk elinkr
eliknr elikrn elnirk elnikr elnrik elnrki elnkri elnkir elkinr elkirn elknir
elknri elkrni elkrin eilrnk eilrkn eilnrk eilnkr eilknr eilkrn eirlnk eirlkn
eirnlk eirnkl eirknl eirkln einrlk einrkl einlrk einlkr einklr einkrl eikrnl
eikrln eiknrl eiknlr eiklnr eiklrn enlirk enlikr enlrik enlrki enlkri enlkir
enilrk enilkr enirlk enirkl enikrl eniklr enrilk enrikl enrlik enrlki enrkli
enrkil enkirl enkilr enkril enkrli enklri enklir eklinr eklirn eklnir eklnri
eklrni eklrin ekilnr ekilrn ekinlr ekinrl ekirnl ekirln eknilr eknirl eknlir
eknlri eknrli eknril ekrinl ekriln ekrnil ekrnli ekrlni ekrlin lerink lerikn
lernik lernki lerkni lerkin leirnk leirkn leinrk leinkr leiknr leikrn lenirk
lenikr lenrik lenrki lenkri lenkir lekinr lekirn leknir leknri lekrni lekrin
lreink lreikn lrenik lrenki lrekni lrekin lrienk lriekn lrinek lrinke lrikne
lriken lrniek lrnike lrneik lrneki lrnkei lrnkie lrkine lrkien lrknie lrknei
lrkeni lrkein lirenk lirekn lirnek lirnke lirkne lirken liernk lierkn lienrk
lienkr lieknr liekrn linerk linekr linrek linrke linkre linker likenr likern
likner liknre likrne likren lnriek lnrike lnreik lnreki lnrkei lnrkie lnirek
lnirke lnierk lniekr lniker lnikre lneirk lneikr lnerik lnerki lnekri lnekir
lnkier lnkire lnkeir lnkeri lnkrei lnkrie lkrine lkrien lkrnie lkrnei lkreni
lkrein lkirne lkiren lkinre lkiner lkienr lkiern lknire lknier lknrie lknrei
lkneri lkneir lkeinr lkeirn lkenir lkenri lkerni lkerin ielrnk ielrkn ielnrk
ielnkr ielknr ielkrn ierlnk ierlkn iernlk iernkl ierknl ierkln ienrlk ienrkl
ienlrk ienlkr ienklr ienkrl iekrnl iekrln ieknrl ieknlr ieklnr ieklrn ilernk
ilerkn ilenrk ilenkr ileknr ilekrn ilrenk ilrekn ilrnek ilrnke ilrkne ilrken
ilnrek ilnrke ilnerk ilnekr ilnker ilnkre ilkrne ilkren ilknre ilkner ilkenr
ilkern irlenk irlekn irlnek irlnke irlkne irlken irelnk irelkn irenlk irenkl
ireknl irekln irnelk irnekl irnlek irnlke irnkle irnkel irkenl irkeln irknel
irknle irklne irklen inlrek inlrke inlerk inlekr inlker inlkre inrlek inrlke
inrelk inrekl inrkel inrkle inerlk inerkl inelrk inelkr ineklr inekrl inkrel
inkrle inkerl inkelr inkler inklre iklrne iklren iklnre iklner iklenr iklern
ikrlne ikrlen ikrnle ikrnel ikrenl ikreln iknrle iknrel iknlre iknler iknelr
iknerl ikernl ikerln ikenrl ikenlr ikelnr ikelrn nelirk nelikr nelrik nelrki
nelkri nelkir neilrk neilkr neirlk neirkl neikrl neiklr nerilk nerikl nerlik
nerlki nerkli nerkil nekirl nekilr nekril nekrli neklri neklir nleirk nleikr
nlerik nlerki nlekri nlekir nlierk nliekr nlirek nlirke nlikre nliker nlriek
nlrike nlreik nlreki nlrkei nlrkie nlkire nlkier nlkrie nlkrei nlkeri nlkeir
nilerk nilekr nilrek nilrke nilkre nilker nielrk nielkr nierlk nierkl niekrl
nieklr nirelk nirekl nirlek nirlke nirkle nirkel nikerl nikelr nikrel nikrle
niklre nikler nrliek nrlike nrleik nrleki nrlkei nrlkie nrilek nrilke nrielk
nriekl nrikel nrikle nreilk nreikl nrelik nrelki nrekli nrekil nrkiel nrkile
nrkeil nrkeli nrklei nrklie nklire nklier nklrie nklrei nkleri nkleir nkilre
nkiler nkirle nkirel nkierl nkielr nkrile nkriel nkrlie nkrlei nkreli nkreil
nkeirl nkeilr nkeril nkerli nkelri nkelir kelinr kelirn kelnir kelnri kelrni
kelrin keilnr keilrn keinlr keinrl keirnl keirln kenilr kenirl kenlir kenlri
kenrli kenril kerinl keriln kernil kernli kerlni kerlin kleinr kleirn klenir
klenri klerni klerin klienr kliern kliner klinre klirne kliren klnier klnire
klneir klneri klnrei klnrie klrine klrien klrnie klrnei klreni klrein kilenr
kilern kilner kilnre kilrne kilren kielnr kielrn kienlr kienrl kiernl kierln
kinelr kinerl kinler kinlre kinrle kinrel kirenl kireln kirnel kirnle kirlne
kirlen knlier knlire knleir knleri knlrei knlrie kniler knilre knielr knierl
knirel knirle kneilr kneirl knelir knelri knerli kneril knriel knrile knreil
knreli knrlei knrlie krline krlien krlnie krlnei krleni krlein krilne krilen
krinle krinel krienl krieln krnile krniel krnlie krnlei krneli krneil kreinl
kreiln krenil krenli krelni krelin

Read more ...[1] , [2] , [3]

History of cryptography
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