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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: oberas
cipher variations:
pcfsbt qdgtcu rehudv sfivew tgjwfx
uhkxgy vilyhz wjmzia xknajb ylobkc
zmpcld anqdme borenf cpsfog dqtgph
eruhqi fsvirj gtwjsk huxktl ivylum
jwzmvn kxanwo lyboxp mzcpyq nadqzr

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: oberas
Cipher: lyvizh

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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: oberas

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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: oberas
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: oberas
Cipher: borenf

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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: oberas
Cipher: 432151241134

Extended Methods:
Method #1

Plaintext: oberas
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
o b e r a s 
4 2 5 2 1 3 
3 1 1 4 1 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: oberas
Cipher: iklcqq

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Method #3

Plaintext: oberas
method variations:
hvfdlt vfdlth fdlthv
dlthvf lthvfd thvfdl

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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: oberas

all 720 cipher variations:
oberas obersa obears obeasr obesar obesra obreas obresa obraes obrase obrsae
obrsea obares obarse obaers obaesr obaser obasre obsrae obsrea obsare obsaer
obsear obsera oebras oebrsa oebars oebasr oebsar oebsra oerbas oerbsa oerabs
oerasb oersab oersba oearbs oearsb oeabrs oeabsr oeasbr oeasrb oesrab oesrba
oesarb oesabr oesbar oesbra orebas orebsa oreabs oreasb oresab oresba orbeas
orbesa orbaes orbase orbsae orbsea orabes orabse oraebs oraesb oraseb orasbe
orsbae orsbea orsabe orsaeb orseab orseba oaerbs oaersb oaebrs oaebsr oaesbr
oaesrb oarebs oaresb oarbes oarbse oarsbe oarseb oabres oabrse oabers oabesr
oabser oabsre oasrbe oasreb oasbre oasber oasebr oaserb oserab oserba osearb
oseabr osebar osebra osreab osreba osraeb osrabe osrbae osrbea osareb osarbe
osaerb osaebr osaber osabre osbrae osbrea osbare osbaer osbear osbera boeras
boersa boears boeasr boesar boesra boreas boresa boraes borase borsae borsea
boares boarse boaers boaesr boaser boasre bosrae bosrea bosare bosaer bosear
bosera beoras beorsa beoars beoasr beosar beosra beroas berosa beraos beraso
bersao bersoa bearos bearso beaors beaosr beasor beasro besrao besroa besaro
besaor besoar besora breoas breosa breaos breaso bresao bresoa broeas broesa
broaes broase brosae brosea braoes braose braeos braeso braseo brasoe brsoae
brsoea brsaoe brsaeo brseao brseoa baeros baerso baeors baeosr baesor baesro
bareos bareso baroes barose barsoe barseo baores baorse baoers baoesr baoser
baosre basroe basreo basore basoer baseor basero bserao bseroa bsearo bseaor
bseoar bseora bsreao bsreoa bsraeo bsraoe bsroae bsroea bsareo bsaroe bsaero
bsaeor bsaoer bsaore bsorae bsorea bsoare bsoaer bsoear bsoera eboras eborsa
eboars eboasr ebosar ebosra ebroas ebrosa ebraos ebraso ebrsao ebrsoa ebaros
ebarso ebaors ebaosr ebasor ebasro ebsrao ebsroa ebsaro ebsaor ebsoar ebsora
eobras eobrsa eobars eobasr eobsar eobsra eorbas eorbsa eorabs eorasb eorsab
eorsba eoarbs eoarsb eoabrs eoabsr eoasbr eoasrb eosrab eosrba eosarb eosabr
eosbar eosbra erobas erobsa eroabs eroasb erosab erosba erboas erbosa erbaos
erbaso erbsao erbsoa erabos erabso eraobs eraosb erasob erasbo ersbao ersboa
ersabo ersaob ersoab ersoba eaorbs eaorsb eaobrs eaobsr eaosbr eaosrb earobs
earosb earbos earbso earsbo earsob eabros eabrso eabors eabosr eabsor eabsro
easrbo easrob easbro easbor easobr easorb esorab esorba esoarb esoabr esobar
esobra esroab esroba esraob esrabo esrbao esrboa esarob esarbo esaorb esaobr
esabor esabro esbrao esbroa esbaro esbaor esboar esbora rbeoas rbeosa rbeaos
rbeaso rbesao rbesoa rboeas rboesa rboaes rboase rbosae rbosea rbaoes rbaose
rbaeos rbaeso rbaseo rbasoe rbsoae rbsoea rbsaoe rbsaeo rbseao rbseoa reboas
rebosa rebaos rebaso rebsao rebsoa reobas reobsa reoabs reoasb reosab reosba
reaobs reaosb reabos reabso reasbo reasob resoab resoba resaob resabo resbao
resboa roebas roebsa roeabs roeasb roesab roesba robeas robesa robaes robase
robsae robsea roabes roabse roaebs roaesb roaseb roasbe rosbae rosbea rosabe
rosaeb roseab roseba raeobs raeosb raebos raebso raesbo raesob raoebs raoesb
raobes raobse raosbe raoseb raboes rabose rabeos rabeso rabseo rabsoe rasobe
rasoeb rasboe rasbeo rasebo raseob rseoab rseoba rseaob rseabo rsebao rseboa
rsoeab rsoeba rsoaeb rsoabe rsobae rsobea rsaoeb rsaobe rsaeob rsaebo rsabeo
rsaboe rsboae rsboea rsbaoe rsbaeo rsbeao rsbeoa aberos aberso abeors abeosr
abesor abesro abreos abreso abroes abrose abrsoe abrseo abores aborse aboers
aboesr aboser abosre absroe absreo absore absoer abseor absero aebros aebrso
aebors aebosr aebsor aebsro aerbos aerbso aerobs aerosb aersob aersbo aeorbs
aeorsb aeobrs aeobsr aeosbr aeosrb aesrob aesrbo aesorb aesobr aesbor aesbro
arebos arebso areobs areosb aresob aresbo arbeos arbeso arboes arbose arbsoe
arbseo arobes arobse aroebs aroesb aroseb arosbe arsboe arsbeo arsobe arsoeb
arseob arsebo aoerbs aoersb aoebrs aoebsr aoesbr aoesrb aorebs aoresb aorbes
aorbse aorsbe aorseb aobres aobrse aobers aobesr aobser aobsre aosrbe aosreb
aosbre aosber aosebr aoserb aserob aserbo aseorb aseobr asebor asebro asreob
asrebo asroeb asrobe asrboe asrbeo asoreb asorbe asoerb asoebr asober asobre
asbroe asbreo asbore asboer asbeor asbero sberao sberoa sbearo sbeaor sbeoar
sbeora sbreao sbreoa sbraeo sbraoe sbroae sbroea sbareo sbaroe sbaero sbaeor
sbaoer sbaore sborae sborea sboare sboaer sboear sboera sebrao sebroa sebaro
sebaor seboar sebora serbao serboa serabo seraob seroab seroba searbo searob
seabro seabor seaobr seaorb seorab seorba seoarb seoabr seobar seobra srebao
sreboa sreabo sreaob sreoab sreoba srbeao srbeoa srbaeo srbaoe srboae srboea
srabeo sraboe sraebo sraeob sraoeb sraobe srobae srobea sroabe sroaeb sroeab
sroeba saerbo saerob saebro saebor saeobr saeorb sarebo sareob sarbeo sarboe
sarobe saroeb sabreo sabroe sabero sabeor saboer sabore saorbe saoreb saobre
saober saoebr saoerb soerab soerba soearb soeabr soebar soebra soreab soreba
soraeb sorabe sorbae sorbea soareb soarbe soaerb soaebr soaber soabre sobrae
sobrea sobare sobaer sobear sobera

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History of cryptography
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