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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: ranids
cipher variations:
sbojet tcpkfu udqlgv vermhw wfsnix
xgtojy yhupkz zivqla ajwrmb bkxsnc
clytod dmzupe enavqf fobwrg gpcxsh
hqdyti irezuj jsfavk ktgbwl luhcxm
mvidyn nwjezo oxkfap pylgbq qzmhcr

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: ranids
Cipher: izmrwh

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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: ranids

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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: ranids
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: ranids
Cipher: enavqf

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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: ranids
Cipher: 241133424134

Extended Methods:
Method #1

Plaintext: ranids
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
r a n i d s 
2 1 3 4 4 3 
4 1 3 2 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: ranids
Cipher: bsodhq

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Method #3

Plaintext: ranids
method variations:
dlsrli lsrlid srlidl
rlidls lidlsr idlsrl

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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: ranids

all 720 cipher variations:
ranids ranisd randis randsi ransdi ransid rainds rainsd raidns raidsn raisdn
raisnd radins radisn radnis radnsi radsni radsin rasidn rasind rasdin rasdni
rasndi rasnid rnaids rnaisd rnadis rnadsi rnasdi rnasid rniads rniasd rnidas
rnidsa rnisda rnisad rndias rndisa rndais rndasi rndsai rndsia rnsida rnsiad
rnsdia rnsdai rnsadi rnsaid rinads rinasd rindas rindsa rinsda rinsad riands
riansd riadns riadsn riasdn riasnd ridans ridasn ridnas ridnsa ridsna ridsan
risadn risand risdan risdna risnda risnad rdnias rdnisa rdnais rdnasi rdnsai
rdnsia rdinas rdinsa rdians rdiasn rdisan rdisna rdains rdaisn rdanis rdansi
rdasni rdasin rdsian rdsina rdsain rdsani rdsnai rdsnia rsnida rsniad rsndia
rsndai rsnadi rsnaid rsinda rsinad rsidna rsidan rsiadn rsiand rsdina rsdian
rsdnia rsdnai rsdani rsdain rsaidn rsaind rsadin rsadni rsandi rsanid arnids
arnisd arndis arndsi arnsdi arnsid arinds arinsd aridns aridsn arisdn arisnd
ardins ardisn ardnis ardnsi ardsni ardsin arsidn arsind arsdin arsdni arsndi
arsnid anrids anrisd anrdis anrdsi anrsdi anrsid anirds anirsd anidrs anidsr
anisdr anisrd andirs andisr andris andrsi andsri andsir ansidr ansird ansdir
ansdri ansrdi ansrid ainrds ainrsd aindrs aindsr ainsdr ainsrd airnds airnsd
airdns airdsn airsdn airsnd aidrns aidrsn aidnrs aidnsr aidsnr aidsrn aisrdn
aisrnd aisdrn aisdnr aisndr aisnrd adnirs adnisr adnris adnrsi adnsri adnsir
adinrs adinsr adirns adirsn adisrn adisnr adrins adrisn adrnis adrnsi adrsni
adrsin adsirn adsinr adsrin adsrni adsnri adsnir asnidr asnird asndir asndri
asnrdi asnrid asindr asinrd asidnr asidrn asirdn asirnd asdinr asdirn asdnir
asdnri asdrni asdrin asridn asrind asrdin asrdni asrndi asrnid narids narisd
nardis nardsi narsdi narsid nairds nairsd naidrs naidsr naisdr naisrd nadirs
nadisr nadris nadrsi nadsri nadsir nasidr nasird nasdir nasdri nasrdi nasrid
nraids nraisd nradis nradsi nrasdi nrasid nriads nriasd nridas nridsa nrisda
nrisad nrdias nrdisa nrdais nrdasi nrdsai nrdsia nrsida nrsiad nrsdia nrsdai
nrsadi nrsaid nirads nirasd nirdas nirdsa nirsda nirsad niards niarsd niadrs
niadsr niasdr niasrd nidars nidasr nidras nidrsa nidsra nidsar nisadr nisard
nisdar nisdra nisrda nisrad ndrias ndrisa ndrais ndrasi ndrsai ndrsia ndiras
ndirsa ndiars ndiasr ndisar ndisra ndairs ndaisr ndaris ndarsi ndasri ndasir
ndsiar ndsira ndsair ndsari ndsrai ndsria nsrida nsriad nsrdia nsrdai nsradi
nsraid nsirda nsirad nsidra nsidar nsiadr nsiard nsdira nsdiar nsdria nsdrai
nsdari nsdair nsaidr nsaird nsadir nsadri nsardi nsarid ianrds ianrsd iandrs
iandsr iansdr iansrd iarnds iarnsd iardns iardsn iarsdn iarsnd iadrns iadrsn
iadnrs iadnsr iadsnr iadsrn iasrdn iasrnd iasdrn iasdnr iasndr iasnrd inards
inarsd inadrs inadsr inasdr inasrd inrads inrasd inrdas inrdsa inrsda inrsad
indras indrsa indars indasr indsar indsra insrda insrad insdra insdar insadr
insard irnads irnasd irndas irndsa irnsda irnsad irands iransd iradns iradsn
irasdn irasnd irdans irdasn irdnas irdnsa irdsna irdsan irsadn irsand irsdan
irsdna irsnda irsnad idnras idnrsa idnars idnasr idnsar idnsra idrnas idrnsa
idrans idrasn idrsan idrsna idarns idarsn idanrs idansr idasnr idasrn idsran
idsrna idsarn idsanr idsnar idsnra isnrda isnrad isndra isndar isnadr isnard
isrnda isrnad isrdna isrdan isradn isrand isdrna isdran isdnra isdnar isdanr
isdarn isardn isarnd isadrn isadnr isandr isanrd danirs danisr danris danrsi
dansri dansir dainrs dainsr dairns dairsn daisrn daisnr darins darisn darnis
darnsi darsni darsin dasirn dasinr dasrin dasrni dasnri dasnir dnairs dnaisr
dnaris dnarsi dnasri dnasir dniars dniasr dniras dnirsa dnisra dnisar dnrias
dnrisa dnrais dnrasi dnrsai dnrsia dnsira dnsiar dnsria dnsrai dnsari dnsair
dinars dinasr dinras dinrsa dinsra dinsar dianrs diansr diarns diarsn diasrn
diasnr dirans dirasn dirnas dirnsa dirsna dirsan disarn disanr disran disrna
disnra disnar drnias drnisa drnais drnasi drnsai drnsia drinas drinsa drians
driasn drisan drisna drains draisn dranis dransi drasni drasin drsian drsina
drsain drsani drsnai drsnia dsnira dsniar dsnria dsnrai dsnari dsnair dsinra
dsinar dsirna dsiran dsiarn dsianr dsrina dsrian dsrnia dsrnai dsrani dsrain
dsairn dsainr dsarin dsarni dsanri dsanir sanidr sanird sandir sandri sanrdi
sanrid saindr sainrd saidnr saidrn sairdn sairnd sadinr sadirn sadnir sadnri
sadrni sadrin saridn sarind sardin sardni sarndi sarnid snaidr snaird snadir
snadri snardi snarid sniadr sniard snidar snidra snirda snirad sndiar sndira
sndair sndari sndrai sndria snrida snriad snrdia snrdai snradi snraid sinadr
sinard sindar sindra sinrda sinrad siandr sianrd siadnr siadrn siardn siarnd
sidanr sidarn sidnar sidnra sidrna sidran siradn sirand sirdan sirdna sirnda
sirnad sdniar sdnira sdnair sdnari sdnrai sdnria sdinar sdinra sdianr sdiarn
sdiran sdirna sdainr sdairn sdanir sdanri sdarni sdarin sdrian sdrina sdrain
sdrani sdrnai sdrnia srnida srniad srndia srndai srnadi srnaid srinda srinad
sridna sridan sriadn sriand srdina srdian srdnia srdnai srdani srdain sraidn
sraind sradin sradni srandi sranid

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History of cryptography
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