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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: reints
cipher variations:
sfjout tgkpvu uhlqwv vimrxw wjnsyx
xkotzy ylpuaz zmqvba anrwcb bosxdc
cptyed dquzfe ervagf fswbhg gtxcih
huydji ivzekj jwaflk kxbgml lychnm
mzdion naejpo obfkqp pcglrq qdhmsr

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: reints
Cipher: ivrmgh

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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: reints

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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: reints
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: reints
Cipher: ervagf

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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: reints
Cipher: 245142334434

Extended Methods:
Method #1

Plaintext: reints
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 i n t s 
2 5 4 3 4 3 
4 1 2 3 4 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: reints
Cipher: woodmt

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Method #3

Plaintext: reints
method variations:
yqmsoi qmsoiy msoiyq
soiyqm oiyqms iyqmso

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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: reints

all 720 cipher variations:
reints reinst reitns reitsn reistn reisnt renits renist rentis rentsi rensti
rensit retnis retnsi retins retisn retsin retsni resnti resnit restni restin
resitn resint rients rienst rietns rietsn riestn riesnt rinets rinest rintes
rintse rinste rinset ritnes ritnse ritens ritesn ritsen ritsne risnte risnet
ristne risten risetn risent rniets rniest rnites rnitse rniste rniset rneits
rneist rnetis rnetsi rnesti rnesit rnteis rntesi rnties rntise rntsie rntsei
rnseti rnseit rnstei rnstie rnsite rnsiet rtines rtinse rtiens rtiesn rtisen
rtisne rtnies rtnise rtneis rtnesi rtnsei rtnsie rtenis rtensi rteins rteisn
rtesin rtesni rtsnei rtsnie rtseni rtsein rtsien rtsine rsinte rsinet rsitne
rsiten rsietn rsient rsnite rsniet rsntie rsntei rsneti rsneit rstnie rstnei
rstine rstien rstein rsteni rsenti rsenit rsetni rsetin rseitn rseint erints
erinst eritns eritsn eristn erisnt ernits ernist erntis erntsi ernsti ernsit
ertnis ertnsi ertins ertisn ertsin ertsni ersnti ersnit erstni erstin ersitn
ersint eirnts eirnst eirtns eirtsn eirstn eirsnt einrts einrst eintrs eintsr
einstr einsrt eitnrs eitnsr eitrns eitrsn eitsrn eitsnr eisntr eisnrt eistnr
eistrn eisrtn eisrnt enirts enirst enitrs enitsr enistr enisrt enrits enrist
enrtis enrtsi enrsti enrsit entris entrsi entirs entisr entsir entsri ensrti
ensrit enstri enstir ensitr ensirt etinrs etinsr etirns etirsn etisrn etisnr
etnirs etnisr etnris etnrsi etnsri etnsir etrnis etrnsi etrins etrisn etrsin
etrsni etsnri etsnir etsrni etsrin etsirn etsinr esintr esinrt esitnr esitrn
esirtn esirnt esnitr esnirt esntir esntri esnrti esnrit estnir estnri estinr
estirn estrin estrni esrnti esrnit esrtni esrtin esritn esrint iernts iernst
iertns iertsn ierstn iersnt ienrts ienrst ientrs ientsr ienstr iensrt ietnrs
ietnsr ietrns ietrsn ietsrn ietsnr iesntr iesnrt iestnr iestrn iesrtn iesrnt
irents irenst iretns iretsn irestn iresnt irnets irnest irntes irntse irnste
irnset irtnes irtnse irtens irtesn irtsen irtsne irsnte irsnet irstne irsten
irsetn irsent inrets inrest inrtes inrtse inrste inrset inerts inerst inetrs
inetsr inestr inesrt inters intesr intres intrse intsre intser insetr insert
inster instre insrte insret itrnes itrnse itrens itresn itrsen itrsne itnres
itnrse itners itnesr itnser itnsre itenrs itensr iterns itersn itesrn itesnr
itsner itsnre itsenr itsern itsren itsrne isrnte isrnet isrtne isrten isretn
isrent isnrte isnret isntre isnter isnetr isnert istnre istner istrne istren
istern istenr isentr isenrt isetnr isetrn isertn isernt neirts neirst neitrs
neitsr neistr neisrt nerits nerist nertis nertsi nersti nersit netris netrsi
netirs netisr netsir netsri nesrti nesrit nestri nestir nesitr nesirt nierts
nierst nietrs nietsr niestr niesrt nirets nirest nirtes nirtse nirste nirset
nitres nitrse niters nitesr nitser nitsre nisrte nisret nistre nister nisetr
nisert nriets nriest nrites nritse nriste nriset nreits nreist nretis nretsi
nresti nresit nrteis nrtesi nrties nrtise nrtsie nrtsei nrseti nrseit nrstei
nrstie nrsite nrsiet ntires ntirse ntiers ntiesr ntiser ntisre ntries ntrise
ntreis ntresi ntrsei ntrsie nteris ntersi nteirs nteisr ntesir ntesri ntsrei
ntsrie ntseri ntseir ntsier ntsire nsirte nsiret nsitre nsiter nsietr nsiert
nsrite nsriet nsrtie nsrtei nsreti nsreit nstrie nstrei nstire nstier nsteir
nsteri nserti nserit nsetri nsetir nseitr nseirt teinrs teinsr teirns teirsn
teisrn teisnr tenirs tenisr tenris tenrsi tensri tensir ternis ternsi terins
terisn tersin tersni tesnri tesnir tesrni tesrin tesirn tesinr tienrs tiensr
tierns tiersn tiesrn tiesnr tiners tinesr tinres tinrse tinsre tinser tirnes
tirnse tirens tiresn tirsen tirsne tisnre tisner tisrne tisren tisern tisenr
tniers tniesr tnires tnirse tnisre tniser tneirs tneisr tneris tnersi tnesri
tnesir tnreis tnresi tnries tnrise tnrsie tnrsei tnseri tnseir tnsrei tnsrie
tnsire tnsier trines trinse triens triesn trisen trisne trnies trnise trneis
trnesi trnsei trnsie trenis trensi treins treisn tresin tresni trsnei trsnie
trseni trsein trsien trsine tsinre tsiner tsirne tsiren tsiern tsienr tsnire
tsnier tsnrie tsnrei tsneri tsneir tsrnie tsrnei tsrine tsrien tsrein tsreni
tsenri tsenir tserni tserin tseirn tseinr seintr seinrt seitnr seitrn seirtn
seirnt senitr senirt sentir sentri senrti senrit setnir setnri setinr setirn
setrin setrni sernti sernit sertni sertin seritn serint sientr sienrt sietnr
sietrn siertn siernt sinetr sinert sinter sintre sinrte sinret sitner sitnre
sitenr sitern sitren sitrne sirnte sirnet sirtne sirten siretn sirent snietr
sniert sniter snitre snirte sniret sneitr sneirt snetir snetri snerti snerit
snteir snteri sntier sntire sntrie sntrei snreti snreit snrtei snrtie snrite
snriet stiner stinre stienr stiern stiren stirne stnier stnire stneir stneri
stnrei stnrie stenir stenri steinr steirn sterin sterni strnei strnie streni
strein strien strine srinte srinet sritne sriten srietn srient srnite srniet
srntie srntei srneti srneit srtnie srtnei srtine srtien srtein srteni srenti
srenit sretni sretin sreitn sreint

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History of cryptography
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